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HUMAN REPRODUCTION, Focus Area Notes -2022 Exam, MALE REPRODUCTIVE SYSTEM, Male reproductive system includes, ,  a pair of testes,,  accessory ducts,,  accessory glands and,  external genitalia., , TESTES, , , Testes is the organ in which sperms are produced., , , , It is oval in shape with a length of about 4 to 5 cm and a width of about 2 to 3 cm ., , Scrotum and its Importance,  The testes are situated outside the abdominal cavity within a pouch called, scrotum., ,  Scrotum maintains the temperature of the testes 2- 2.5 degree celsius lower than, the normal internal body temperature which is necessary for spermatogenesis., , Testicular lobules,  Each testes has about 250 compartments called testicular lobules ., Seminiferous tubules,  Each testicular lobule contains one to three highly coiled tubules called, seminiferous tubules . Sperms are produced here ., , Three types of cells in testes,  Spermatogonial cells (Male germ Cells),  Sertoli cells,  Interstitial cells or Leydig cells, Spermatogonial cells (Male germ Cells),  The cells which lines the inner surface of, spermatogonial cells., 1, , seminiferous tubule is called

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, , These cells undergo meiotic division and transforms in to sperms ., , Sertoli cells .,  These cells are also present in the inner surface of seminiferous tubule.,  Sertoli cells provide nutrition to the germ cells, , Interstitial cells or Leydig cells,  These cells synthesise and secrete the hormones called androgens., , The male sex accessory ducts, The male sex accessory ducts include, ,  rete testis ,,  vasa efferentia ,,  epididymis and,  vas deferens.,  Accessory ducts store and transport the sperms from the testis to the outside, through urethra., ,  The urethra (ejaculatory duct) originates from the urinary bladder and extends, through the penis to its external opening called urethral meatus, , 2

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Flow chart of conduction of sperms through accessory ducts, , Penis,  The penis is the male external genitalia.,  It is made up of special tissue that helps in erection of the penis to facilitate, insemination., ,  The enlarged end of penis called the glans penis is covered by a loose fold of skin, called foreskin., , The male sex accessory glands, The male sex accessory glands include paired, ,  paired seminal vesicles ,,  a prostate gland,  paired bulbourethral glands .,  Secretion of these glands constitute the seminal plasma which is rich in fructose ,, calcium and certain enzymes ., ,  The secretion of bulbourethral glands also help in the lubrication of the penis, , 3

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THE FEMALE REPRODUCTIVE SYSTEM, The female reproductive system consists of,  a pair of ovaries,, ,  a pair of oviducts,,  uterus,,  cervix,,  vagina and the,  external genitalia located in pelvic region., OVARY,  Ovaries are the primary female sex organs that produce the female, gamete (ovum) and several steroid hormones (ovarian hormones)., ,  Each ovary is about 2 to 4 cm in length and is connected to the pelvic wall and, uterus by ligaments., ,  The outer part of the ovary is called cortex and inner medulla ., , Oviducts (Fallopian tubes), Oviduct has the following parts, ,  Fimbriae,  Infundibulum,  Ampulla,  Isthmus,  The funnel shaped part closer to the ovary is the infundibulum.,  The finger like projections in the edges of the infundibulum is called fimbriae.,  Fimbriae help in collection of the ovum after ovulation.,  The wider part after infundibulum of the oviduct is called ampulla.,  The last part of the oviduct which joins the uterus is called isthmus., , Uterus (womb), The uterus is single and it is also called womb., The shape of the uterus is like an inverted pear., It is supported by ligaments attached to the pelvic wall., , 4

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Cervix., The uterus opens into vagina through a narrow cervix., The cavity of the cervix is called cervical canal, , Birth Canal,  Cervical canal along with vagina forms the birth canal., Wall of Uterus, , , The wall of the uterus has three layers of tissue., ,  Perimetrium,  Myometrium,  Endometrium,  Perimetrium is the external thin membrane .,  Myometrium is the middle thick membrane made up of smooth muscles , which, exhibit strong contraction during delivery of the baby ., ,  Endometrium, , is the inner glandular layer that lines the uterine cavity, , Endometrium undergoes cyclical changes during menstrual cycle ., , 5

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FEMALE EXTERNAL GENITALIA, The female external genitalia includes, ,  mons pubis,,  labia majora,,  labia minora,,  hymen,,  and clitoris.,  Mons pubis is a cushion of fatty tissue covered by skin and pubic hair .,  The labia majora are fleshy folds of tissue , which extend down from the mons, pubis and surround the vaginal opening ., ,  The labia minora are paired folds of tissue under the labia majora .,  Hymen is the thin ring of tissue partially covering the vaginal opening.,  Clitoris is the tiny finger like structure which lies at the upper junction of the two, labia minora above the urethral opening, The presence or absence of hymen is not a reliable indicator of virginity or sexual, experience. Justfy, ,  The hymen is often torn during the first coitus (intercourse).,  It can also be broken by a sudden fall or jolt, insertion of a vaginal tampon, active, participation in some sports like horseback riding, cycling, etc., ,  In some women the hymen persists even after coitus.,  So the presence or absence of hymen is not a reliable indicator of virginity or sexual, experience, , MAMMARY GLANDS, , , The mammary glands are paired structures (breasts) that contain glandular tissue, and variable amount of fat., , , , The glandular tissue of each breast is divided into 15-20 mammary lobes, containing clusters of cells called alveoli., , , , The cells of alveoli secrete milk, which is stored in the cavities (lumens) of alveoli., , , , The alveoli open into mammary tubules., , , , The tubules of each lobe join to form a mammary duct., 6

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, , Several mammary ducts join to form a wider mammary ampulla which is, connected to lactiferous duct through which milk is sucked out., , GAMETOGENESIS, , , Gametogenesis is the formation of male and female gametes ., , , , Formation of male gamete is spermatogenesis and female gamete is oogenesis., , SPERMATOGENESIS,  Spermatogenesis begins at puberty .,  The spermatogonial cells present on the inside wall of the seminiferous tubules, multiply by mitotic division and increase in numbers ., ,  Each spermatogonium is diploid and contains 46 chromosomes ., Primary spermatocytes,  Spermatogonial cells synthesize cellular materials and stores food and grows., After growth it is known as primary spermatocytes., 7

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Secondary spermatocyte,  Primary spermatocyte undergoes the first meiotic division and two haploid, secondary spermatocyte are formed.(have 23 chromosomes), , Spermatids,  Secondary spermatocytes undergoes second meiotic division and four haploid, spermatids are formed., , Spermiogenesis,  It is the transformation of spermatids in to functional spermatozoa or sperms., Spermiation,  After spermiogenesis sperm heads become embedded in the sertoli cells ,and are, finally released from the seminiferous tubules by the process called spermiation ., , 8

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Function of Acrosome,  The sperm head contains a cap-like structure called acrosome.,  The acrosome is filled with enzymes that help fertilisation of the, ovum., OOGENESIS,  The process of formation of a mature female gamete is called oogenesis.,  Oogenesis is initiated during the embryonic stage,  No more oogonia are formed and added after birth., , Primary oocytes,  Oogonial cells start division and enter into prophase-I of the meiotic division and get, temporarily arrested at that stage, called primary oocytes., , Primary follicle, , , Each primary oocytes gets surrounded by a layer of granulosa cells and is called, the primary follicle., , , , A large number of primary follicles degenerate during the phase from birth to, puberty., , , , At puberty only 60,000-80,000 primary follicles are left in each ovary., 10

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Secondary follicles, , , The primary follicles get surrounded by more layers of granulosa cells and a new, theca and are called secondary follicles., , Teritiary follicles, , , The secondary follicle transforms into a tertiary follicle., , Antrum, , , The fluid filled cavity in tertiary follicle is called antrum., , Secondary oocyte, , , The primary oocyte within the tertiary follicle grows in size and completes its first, meiotic division and transforms into a large haploid secondary oocyte., , , , Secondary oocyte retains bulk of the nutrient rich cytoplasm of the primary, oocyte., , Polar body,  The functionless tiny cells formed during the unequal cell division of oogenesis is, called polar body, , Graafian follicle, , , The mature tertiary follicle is called Graafian follicle., , Zona pellucida, , , The membrane covering secondary oocyte is called zona pellucida., , Ovulation,  The Graafian follicle ruptures to release the secondary oocyte (ovum).,  The process of release of ovum from the ovary is called ovulation, , 11

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Menarche and Menopause.,  The first menstruation begins at puberty and is called menarche.,  In human beings, menstrual cycles ceases around 50 years of age; that is termed as, menopause., 12

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LH Surge,  LH and FSH secretion from pituitary increases and attains a peak level about 14 th, day known as LH Surge)., , Corpus luteum,  The remaining part of the Graffian follicles after ovulation transforms in to corpus, luteum.,  The corpus luteum secretes large amounts of progesterone which is essential for, the maintenance of the endometrium., , Fertilization,  The process of fusion of a sperm with an ovum is called fertilization ., , Cleavage,  Cleavage is the repeated mitotic division of the zygote, , Blastomeres,  Blastomeres are the cells formed during cleavage, , Morula,  The embryo with 8 to 16 blastomeres is called a morula, , Blastocyst,  The morula continues to divide and transforms into blastocyst.,  The blastomeres in the blastocyst are arranged into an outer layer called, trophoblast and an inner group of cells attached to trophoblast called the inner, cell mass., , Fate of cells in blastocyst,  The trophoblast layer gets attached to the endometrium and the inner cell mass, gets differentiated as the embryo., , 13

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Significance of Colostrum,  Breast-feeding during the initial period of infant growth is recommended, by doctors for bringing up a healthy baby...Why ?,  The milk produced during the initial few days of lactation is called, colostrum which contains several antibodies absolutely essential to, develop immune resistance for the new-born babies., , 15

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TLB’S Biology Classes, , REPRODUCTIVE HEALTH, Focus Area -2022 Exam, **********************************************************************************, ,  Contraceptives can be classified into the following groups, , Natural Methods,  Natural methods work on the principle of avoiding chances of ovum, and sperms meeting., , 1

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TLB’S Biology Classes, , Periodic Abstinence,  In this method couples avoid or abstain from coitus from day 10 to 17 of the, menstrual cycle when ovulation could be expected., ,  As chances of fertilisation are very high during this period, it is called the fertile, period., ,  Therefore, by abstaining from coitus during this period, conception could be, prevented., , Withdrawal/Coitus interruptus,  In this method, the male partner withdraws his penis from the vagina just before, ejaculation so as to avoid insemination., , Lactational amenorrhea,  Lactational amenorrhea (absence of menstruation) method is based on the fact, that ovulation and therefore the cycle do not occur during the period of intense, lactation following parturition., ,  This method has been reported to be effective only upto a maximum period of six, months following parturition., ,  As no medicines or devices are used in these methods, side effects are almost nil.,  Chances of failure in this method are also high., ,  In barrier methods, ovum and sperms are prevented from physically meeting with, the help of barriers., ,  Such methods are available for both males and females., , 2

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TLB’S Biology Classes, , Condoms,  Condoms are barriers made of thin rubber/latex sheath that are used to cover the, penis in the male or vagina and cervix in the female, just before coitus so that the, ejaculated semen would not enter into the female reproductive tract., ,  ‘Nirodh’ is a popular brand of condom for the male.,  Condoms has the benefit of protecting the user from STIs and AIDS., , Diaphragms, cervical caps and vaults,  Diaphragms, cervical caps and vaults are also barriers made of rubber that are, inserted into the female reproductive tract to cover the cervix during coitus., ,  ‘They prevent conception by blocking the entry of sperms through the cervix.,  They are reusable., ,  IUDs are devices inserted in the uterus through vagina with the help of doctors or, expert nurses., They are classified into, , Mode of action of IUDs, ,  IUDs increase phagocytosis of sperms within the uterus and the Cu ions released, suppress sperm motility and the fertilising capacity of sperms., 3

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TLB’S Biology Classes,  The hormone releasing IUDs make the uterus unsuitable for implantation and the, cervix hostile to the sperms., , Oral contraceptives,  Oral administration of progestogens or progestogen–oestrogen combinations in the, form of tablets (pills) are called oral contraceptives., ,  Pills are taken daily for 21 days starting within the first five days of menstrual cycle.,  After a gap of 7 days (during which menstruation occurs) it has to be repeated in, the same pattern till the female desires to prevent conception., , Mode of action of Oral Contraceptives,  They inhibit ovulation and implantation as well as alter the quality of cervical, mucus to prevent/retard entry of sperms., ,  Pills are very effective with lesser side effects., Example,  Saheli –the new oral contraceptive for the females contains a non-steroidal, preparation., ,  It is a ‘once a week’ pill with very few side effects and high contraceptive value., ,  Progestogens alone or in combination with estrogen can also be used by females as, injections or implants under the skin., ,  Their mode of action is similar to that of pills and their effective periods are much, longer., , Emergency Contraceptives,  Administration of progestogens or progestogen-estrogen combinations or IUDs, within 72 hours of coitus have been found to be very effective as emergency, contraceptives., ,  They could be used to avoid possible pregnancy due to rape or casual unprotected, intercourse., , 4

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TLB’S Biology Classes, ,  Surgical methods, also called sterilisation, are generally advised for the, male/female partner as a terminal method to prevent any more pregnancies., ,  Surgical intervention blocks gamete transport and thereby prevent conception., , Vasectomy,  Sterilisation procedure in male.,  In vasectomy, a small part of the vas deferens is removed or tied up through a small, incision on the scrotum., , Tubectomy,  Sterilisation procedure in female.,  In tubectomy, a small part of the fallopian tube is removed or tied up through a, small incision in the abdomen or through vagina., , Demerit of surgical method, These techniques are highly effective but their reversibility is very poor., , Possible ill- Effects of Contraceptives,  Nausea , Abdominal pain , Breakthrough bleeding, Irregular menstrual bleeding, are some of the ill effects of contraceptives., 5

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TLB’S Biology Classes, ,  Infections or diseases which are transmitted through sexual intercourse are, collectively called, ,  sexually transmitted infections (STI) or,  venereal diseases (VD) or reproductive tract infections (RTI)., , Examples -Sexually Transmitted Infections (STIs),  Gonorrhoea,,  syphilis,,  genital herpes,,  chlamydiasis,,  genital warts,,  trichomoniasis,,  hepatitis-B and,  HIV infections leading to AIDS are some of the common STIs., , Mode of transmission of STIs,  Infections like hepatitis–B and HIV can be transmitted by sharing of injection, needles, surgical instruments, etc., with infected persons,, ,  transfusion of blood, or from an infected mother to the foetus too.,  Except for hepatitis-B, genital herpes and HIV infections, other diseases are, completely curable if detected early and treated properly., , Early Symptoms of STIs,  Early symptoms of most of these are minor and include,  itching,,  fluid discharge,,  slight pain, swellings, etc., in the genital region.,  Infected females may often be asymptomatic and hence, may remain undetected for, long., 6

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TLB’S Biology Classes, , Later Symptoms of STIs,  Absence or less significant symptoms in the early stages of infection could lead to, complications in the later stage like, ,  Pelvic Inflammatory Diseases (PID), abortions, still births, ectopic pregnancies,, infertility or even cancer of the reproductive tract., , Preventive measures to avoid STIs, (i) Avoid sex with unknown partners/multiple partners., (ii) Always try to use condoms during coitus., (iii) In case of doubt, one should go to a qualified doctor for early detection and get, complete treatment if diagnosed with infection., , Infertility,  Inability to conceive or produce children even after 2 years of sexual co-habitation, is called infertility ., ,  Specialised health care units (infertility clinics, etc.) could help in diagnosis and, corrective treatment of some of these disorders and enable these couples to have, children., , Reasons for Infertility,  The reasons for infertility may be many–physical,congenital, diseases, drugs,, immunological or even psychological., ,  If corrections in infertility clinics are not possible, the couples could be assisted to, have children through certain special techniques commonly known as assisted, reproductive technologies (ART)., , 7

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TLB’S Biology Classes, , In vitro fertilisation(IVF),  Fertilisation outside the body in almost similar conditions as that in the body is, known as In vitro fertilisation(IVF)., ,  In this method, popularly known as test tube baby programme, ova from the, wife/donor (female) and sperms from the husband/donor (male) are collected and, are induced to form zygote under simulated conditions in the laboratory., ,  The zygote or early embryos is then transferred to fallopian tube or uterus., , ZIFT–zygote intra fallopian transfer,  The zygote or early embryos upto 8 blastomeres is transferred into the fallopian, tube known as ZIFT–zygote intra fallopian transfer., , IUT – intra uterine transfer,  Early embryos with more than 8 blastomeres are transferred into the uterus, known as IUT – intra uterine transfer., , In-vivo fertilisation,  Fusion of gametes within the female is known as in-vivo fertilisation.,  Embryos formed by in-vivo fertilisation is also used for embryo transfer to assist, those females who cannot conceive., , GIFT – gamete intra fallopian transfer, , , Transfer of an ovum collected from a donor into the fallopian tube of another, female who cannot produce one, but can provide suitable environment for, fertilisation and further development is GIFT – gamete intra fallopian transfer, , Intra cytoplasmic sperm injection (ICSI),  It is a method in which the sperm is directly injected into the ovum to form the, zygote in the laboratory., , 8

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TLB’S Biology Classes, , Artificial Insemination (AI),  Infertility cases either due to inability of the male partner to inseminate the female, or due to very low sperm counts in the ejaculates, could be corrected by artificial, insemination (AI) technique., ,  In this technique, the semen collected either from the husband or a healthy donor, is artificially introduced either into the vagina or into the uterus (IUI – intrauterine insemination) of the female., , 9

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TLB’S Biology Classes, , PRINCIPLES OF INHERITANCE AND VARIATION, FOCUS AREA -2022 EXAM, ******************************************************, LAW OF DOMINANCE, (i) Characters are controlled by discrete units called factors., (ii) Factors occur in pairs., (iii) In a dissimilar pair of factors one member of the pair dominates (dominant) the other, (recessive)., LAW OF SEGREGATION, , , , This law states that during gamete formation, the two factors for a character, present in an individual will separate and segregate with each other . So that a, gamete receives only one of the two factors., , ., INCOMPLETE DOMINANCE, , , , The type of inheritance in which the F 1 phenotype do not resemble either of the, two parents but shows an intermediate character is called incomplete dominance., Example, The inheritance of flower colour in the dog flower (snapdragon or Antirrhinum sp), , •, , In a cross between homozygous red flowered plant (RR) with homozygous white, flowered plant(rr) the F 1 (Rr) was pink instead of red., , •, , When F 1 was self fertilized the F 2 resulted the following ratio, 1Red (RR) : 2Pink(Rr) : 1White., , •, , Here the genotypic and phenotypic ratio is 1:2:1., , •, , This happens because R is not completely dominant over r. So Rr shows an, intermediate pink colour, , 1

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TLB’S Biology Classes, , Phenotypic ratio : 1 Red : 2 Pink : 1 White, Genotypic ratio : 1 RR : 2 Rr : 1 rr, Phenotypic ratio = Genotypic ratio, =1:2:1, , Incomplete dominance is a genetic phenomenon in which both, Genotypic and phenotypic ratio are same ie, 1 : 2 : 1, CO –DOMINANCE, •, , It is the phenomenon in which F 1 generation resembles both the parents., , Eg : ABO- Blood group in human beings, •, , The blood group is determined by the sugar polymers present on the plasma, membrane of RBC and which is controlled by the gene I., , 2

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TLB’S Biology Classes, •, , The gene I has three alleles IA , IB & i., , •, , IA and IB produce a slightly different form of the sugar while allele i doesn’t, produce any sugar., , •, , When IA and IB are present together, they both express their own types of sugars., This is due to co-dominance., , Multiple alleles, , , , , More than two alleles of a gene are called multiple alleles and the phenomenon is called, multiple allelesim., ABO-Blood group in man is an excellent example for multiple allelism . Here three alleles, determine the same character., In an individual only two alleles can be present., , Multiple alleles can be found only when population studies are made., , 3

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TLB’S Biology Classes, , A single gene product may produce more than one effect., Substantiate the statement., Eg : Starch synthesis in pea seeds - controlled by one gene, , , , , , , , , Starch synthesis in pea is controlled by two alleles (B and b)., Starch is synthesised effectively by BB homozygotes and therefore, large, starch grains are produced., In bb homozygotes have lesser efficiency in starch synthesis and, produce smaller starch grains.., After maturation of the seeds, BB seeds are round and the bb seeds are, wrinkled., Heterozygotes produce round seeds, and so B seems to be the dominant, allele., But, the starch grains produced are of intermediate size in Bb seeds., So if starch grain size is considered as the phenotype, then from this, angle, the alleles show incomplete dominance, , SEX DETERMINATION IN MAN, , XX-XY Mechanism, •, , The chromosome pattern in female is XX and that in the male is XY., , •, , Females are homo gametic with only X chromosomes and males are hetero, gametic and produce gametes with either X or Y chromosomes ., 4

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TLB’S Biology Classes, •, , The XY zygote will be formed if the Y chromosome carrying male gamete fuses, with the X gamete of female, and the child thus formed is male ., , • Female child will born from XX zygote if the X gamete of female fuses with the X, gamete of male ., , Pedigree Analysis, , Pedigree Analysis, , Analysing the inheritance of the character through several previous generations, in a family is known as pedigree analysis., •, •, , In the pedigree analysis the inheritance of a particular trait is represented in the, family tree over generations., pedigree study provides a strong tool, which is utilised to trace the inheritance of, a specific trait, abnormality or disease., , 5

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TLB’S Biology Classes, , Sickle-cell anaemia, •, , Sickle cell anaemia is an autosome linked recessive trait., , •, , The gene for Sickle cell anaemia occurs in chromosome 11., , •, , The defect is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at, the sixth position of the beta globin chain of the haemoglobin molecule., , •, , The substitution of amino acid in the globin protein results due to the single base, substitution at the sixth codon of the beta globin gene from GAG to GUG., , 6

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TLB’S Biology Classes, •, , A, S, The disease is controlled by a single pair of allele, Hb and Hb ., , •, , S, S, Homozygous individuals Hb Hb show the diseased phenotype., , •, , A, S, Heterozygous Hb and Hb individuals are carrier of the disease., , •, , The mutant haemoglobin molecule undergoes polymerisation under low oxygen, tension causing the change in the shape of the RBC from biconcave disc to, elongated sickle like., , 7

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TLB’S Biology Classes, , •, , The possibility of a female becoming a haemophilic is extremely rare because, mother of such a female has to be at least carrier and the father should be, haemophilic (unviable in the later stage of life)., , •, , The family pedigree of Queen Victoria shows a number of haemophilic, descendents as she was a carrier of the disease., , Phenylketonuria, •, •, •, •, •, •, , This is an inborn error of metabolism., It is inherited as the autosomal recessive trait., The affected individual lacks an enzyme that converts the amino acid, phenylalanine into tyrosine., As a result of this phenylalanine is accumulated and converted into, phenylpyruvic acid and other derivatives., Accumulation of these in brain results in mental retardation., These are also excreted through urine because of its poor absorption by kidney., , 8

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TLB’S Biology Classes, , Chromosomal Disorders, Down’s Syndrome, •, •, , This disorder was first described by Langdon Down (1866)., The cause of this genetic disorder is the presence of an additional copy of the, chromosome number 21., The affected individual is, • short statured with small round head,, • furrowed tongue and partially open mouth, • Palm is broad with characteristic palm crease., • Physical, psychomotor and mental development is retarded, , Klinefelter’s Syndrome, •, , This genetic disorder is caused due to the presence of an additional copy of Xchromosome resulting into a karyotype of 47, XXY., , •, , Such an individual has overall masculine development, however, the feminine, development (development of breast, i.e., Gynaecomastia) is also express., , •, , Such individuals are sterile., , 9

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TLB’S Biology Classes, , TURNER’S SYNDROME, •, , Turner’s Syndrome is caused due to the absence of one of the X chromosomes, i.e.,, 45 with X0., , •, , Such females are sterile with rudimentary ovaries, , •, , They lack of other secondary sexual characters., , 10

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1, , MOLECULAR BASIS OF INHERITANCE, FOCUS AREA -HSE EXAM 2022, , The salient features of the Double-helix structure of DNA, i) DNA is made of two polynucleotide chains, where the backbone is constituted, by sugar-phosphate, and the bases project inside., ii) The two chains have anti-parallel polarity. 0ne chain has the polarity 5'->3', the, other has 3'->5'., iii) The bases in two strands are paired through hydrogen bond (H-bonds) forming, base pairs (bp). Adenine forms two hydrogen bonds with Thymine .Similarly,, Guanine is bonded with Cytosine with three H-bonds., iv) The two chains are coiled in a right-handed fashion. The pitch of the helix is 3.4, nm and there are roughly 10 bp in each turn. Consequently, the distance, between a bp in a helix is approximately equal to 0.34 nm., v) The plane of one base pair stacks over the other in double helix. This, in addition, to H-bonds, confers stability of the helical structure, , Central dogma in molecular biology

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2, , Reverse Transcription, , In some viruses the flow of information is in reverse direction, that is,from, RNA to DNA. It is known as Reverse transcription., , REPLICATION OF DNA, •, , Watson and Crick proposed Semiconserve mode of DNA replication., , •, , In semiconservative replication, the newly formed DNA has one old strand and, one new strand., , •, , The two strands separate and act as template for the synthesis of new, complementary strands., , •, , After the completion of replication, each DNA molecule would have one, parental and one newly synthesized strand., , Meselson and Stahl’s Experiment, •, , •, , Mathew Meselson and Franklin Stahl demonstrated the semiconservative mode of, DNA replication in E.coli(1958)., They grew E. coli in a medium containing 15NH4Cl as the only nitrogen source for, many generations., The result was that 15N was incorporated into newly synthesised DNA, , •, , Bacterium thus formed became heavier and the DNA is called heavier DNA, , •, , This heavy DNA molecule is then subjected to centrifugation in a Cesium, , •, , Chloride (CsCl)., •, , Due to higher density 15N DNA deposited at the bottom of the test tube., , •, , Then they transferred the cells into a medium with normal 14NH4Cl (14N, medium) .

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3, •, , Then the DNA was extracted from the culture after one generation(20 minutes), after the transfer from 15N to 14N medium., , •, , Then subjected to centrifugation and found that it had a hybrid or intermediate, density between 15N DNA and 14N DNA., , •, , The DNA that was extracted from the culture after, two generation after the transfer from, , 15, , N to, , 14, , (after 40 minutes), , N medium had composed of, , equal amounts of this hybrid DNA and of ‘light’ DNA., •, , The experiment proved that the two strands of DNA separates at the time of, replication., , •, , After the completion of replication each DNA molecule would have one, parental and one newly synthesised strand., , •, , This scheme of DNA replication is termed as Semiconservative Replication, , •, , Taylor and colleagues in 1958 proved that the DNA in chromosomes also, replicate Semiconservatively., , •, , They conducted experiments in, , Vicia faba (faba beans) by using radioactive, , thymidine., , The Machinery and the Enzymes for DNA Replication, The main enzyme of DNA replication is DNA-dependent DNA Polymerase, , DNA Polymerase, •, , This is one of the fastest enzyme which catalyses the polymerization of, nucleotides with greatest accuracy.

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4, •, , Any defect in replication leads to mutation., , •, , In E.coli, 4.6x10 6 bp completes replication with 38 mts, ie, average rate is 2000, bp per second., , Deoxyribonucleotide triphosphates, •, , Deoxyribonucleotide triphosphates provide energy for replication., , •, , Deoxyribonucleoside triphosphates serve dual purposes., , •, , It act as substrates and also provide energy for polymerisation reaction, , Replication fork, •, , For long DNA molecules, the two strands of DNA cannot be separated in its, entire length due to very high energy requirement., , •, , In such DNAs replication occur within a small opening of the DNA helix, known as replication fork., , Leading strand, •, , The DNA dependent DNA Polymerases catalyses polymerization in 5`->3`, direction only., , •, , In 5`->3` direction , (the template with polarity 3`-> 5`) the replication is, continuous and it is known as leading strand., , Lagging strand, , , In the other strand, template with polarity 5`->3` , the replication is, discontinuous and is called lagging strand., , , , Discontinuously synthesized DNA fragments are called okazaki fragments.

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5, , DNA ligase, , , The discontinuously synthesized okazaki fragments are joined by the enzyme, called DNA ligase., , Origin of Replication, , , The definite regions in which replication originates are known as origin of, replication., , TRANSCRIPTION, , , The process of copying genetic information from one strand of the DNA into, RNA is called transcription., , •, , In transcription only a segment of DNA and only one of the strands is copied, into RNA., , •, , The two DNA strands have opposite polarity and the, , DNA-dependent RNA, , polymerase catalyse the polymerisation of RNA in only one direction, that is, 5', →3' direction., •, , The strand that has the polarity 3'→5' acts as a template, and is referred to as, template strand., , •, , The other strand which has the polarity (5'→3' ) and the sequence same as RNA, is referred to as coding strand., , write the sequence of RNA transcribed from this DNA?, , •, Answer

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6, , Promoter, Promoter is a DNA sequence that provides binding site for RNA, polymerase., It is located towards the 5` end(upstream) of the structural gene., The presence of a promoter in a transcription unit defines the template, and coding strands., , Terminator, The terminator is located towards 3' -end (downstream) of the coding, strand and it usually defines the end of the process of transcription., , Transcription Unit and the Gene, Cistron, , , Cistron is a segment of DNA coding for a polypeptide., , Monocistronic unit, •, , The structural unit in transcription unit of eukaryotes are monocistronic., , •, , Monocistronic structural genes have interrupted coding sequences. Ie, the, genes are split or the genes with coding sequences and genes with noncoding sequences., , Exons,  The coding sequence or expressed sequences of cistron are called, exons., , Introns, The non coding sequences of cistrons are called introns or intervening, sequence. They do not appear in the mature or processed RNA.

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7, , Polycistronic unit, This is the structural transcription unit of bacteria or prokaryotes

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8

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9, , REGULATION OF GENE EXPRESSION, In eukaryotes, the gene expression is regulated at the following levels, (i) transcriptional level (formation of primary transcript),, (ii) processing level (regulation of splicing),, (iii) transport of mRNA from nucleus to the cytoplasm,, (iv) translational level., •, , The gene expression is controlled by metabolic, physiological or, environmental conditions., Example, • The enzyme beta-galactosidase is synthesized by E.coli to catalyse the, hydrolysis of lactose into galactose and glucose., , •, , If the bacteria are living in medium devoid of lactose, they need not require the, particular enzyme., • The development and differentiation of embryo into adult organisms are also a, result of the co-ordinated activities of several set of genes and their, expressions., Operon, •, , Francois Jacob and Jacque Monod were the first to explain regulation of gene, expression at transcriptional level., , •, , A metabolic reaction is controlled by a set of genes is referred to as operon., , Examples of Operon, •, , lac operon, trp operon,ara operon,his operon, val operon, , •, , In lac operon ( lac referes to lactose), a polycistronic structural gene is, regulated by a common promoter gene and regulatory genes., , The Lac operon, •, , Lactose is the substrate for the enzyme beta-galactosidase and it regulates, switching on and off of the operon., , •, , Hence, it is termed as inducer., , Components of Lac operon, Regulatory gene (i gene), , ◦ Regulatory gene produces the repressor protein.

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10, , Promoter gene (P), , ◦ It is the region in which RNA Polymerase binds, Operator gene (O), ◦ It is the region in which repressor protein binds., , Structural gene( z, y,a), , •, , Structural gene transcribe into lac mRNA and it is translated into, lac proteins:-, , β -galactosidase, • z gene codes for beta-galactosidase ( β -gal),, It converts the disaccharide, lactose into galactose and glucose., , •, , The y gene codes for permease, Permease increases permeability of the of the cell to β -galactosides., • The a gene encodes a transacetylase., , Lac operon (In absence of inducer), •, •, •, •, •, , Regulatory gene transcribes into repressor mRNA., Repressor mRNA translates into repressor protein., Repressor protein binds to the Operator region., This binding prevents the RNA Polymerase binding to the Promoter, region., Thus the transcription of the structural genes is prevented.

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11, , Lac operon (In presence of inducer), , •, , Regulatory gene transcribes into repressor mRNA., , •, , Repressor mRNA translates into repressor protein., , •, , inducer, such as lactose or allolactose binds with repressor protein and, it becomes inactive., , •, , Inactive repressor could not bind to operator. So RNA Polymerase binds, to Promoter region., , •, , RNA Polymerase transcribes lac mRNA, , •, , Thus the transcription of the structural genes takes place., , HUMAN GENOME PROJECT (HGP), •, , For sequencing, the total DNA from a cell is isolated and converted into random, fragments of relatively smaller sizes., , •, , Cloned in suitable host using specialised vectors., , BAC & YAC, •, , If bacteria is used as vector then it is called as BAC (bacterial artificial, chromosomes)., , •, , If we use Yeast as vector then it is called YAC (yeast artificial chromosomes)

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12, , Salient Features of Human Genome, (i) The human genome contains 3164.7million bp., (ii) The average gene consists of 3000 bases, but sizes vary greatly, with the largest, known human gene being dystrophin at 2.4 million bases., (iii) The total number of genes is estimated at 30,000– much lower, than previous estimates of 80,000 to 1,40,000 genes., Almost all (99.9 per cent) nucleotide bases are exactly the same in all people., (iv) The functions are unknown for over 50 per cent of the discovered Genes., (v) Less than 2 per cent of the genome codes for proteins., (vi) Repeated sequences make up very large portion of the human genome., (vii) Repetitive sequences are stretches of DNA sequences that are repeated many, times, sometimes hundred to thousand times., They are thought to have no direct coding functions, but they shed light on, chromosome structure, dynamics and evolution., (viii) Chromosome 1 has most genes (2968), and the Y has the fewest (231)., (ix) Scientists have identified about 1.4 million locations where single-base DNA, differences (SNPs – single nucleotide polymorphism, pronounced as ‘snips’) occur, in humans., , DNA FINGERPRINTING, STEPS IN DNA FINGERPRINTING, (i) isolation of DNA,, (ii) digestion of DNA by restriction endonucleases,, (iii) separation of DNA fragments by electrophoresis,, (iv) transferring (blotting) of separated DNA fragments to synthetic, membranes, such as nitrocellulose or nylon,, (v) hybridisation using labelled VNTR probe, and, (vi) detection of hybridised DNA fragments by autoradiography., , Applications of DNA Fingerprinting, •, •, •, •, , DNA from every tissue (such as blood, hair-follicle, skin, bone, saliva, sperm, etc.), from an individual show the same degree of polymorphism, they become, very useful identification tool in forensic applications., It is used as a powerful forensic tool to solve the problems of paternity, rape,, murder etc., It is used in the diagnosis of genetic diseases., It is used in the determination of phylogenetic status of animals etc.

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1, , EVOLUTION, FOCUS AREA -HSE 2022 EXAM, , TLB’S Biology Classes

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TLB’S Biology Classes, , HUMAN HEALTH AND DISEASES, FOCUS AREA -HSE EXAM 2022, COMMON DISEASES IN HUMANS, , 1

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TLB’S Biology Classes, , Side-effects of anabolic steroids in males,  In males it includes acne, increased aggressiveness, mood swings,, depression, reduction of size of the testicles, decreased sperm production,, potential for kidney and liver dysfunction, breast enlargement, premature, baldness, enlargement of the prostate gland., , 13

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TLB’S Biology Classes, , MICROBES IN HUMAN WELFARE, Focus Area-2022 Exam, MICROBES IN HOUSEHOLD PRODUCTS, •, , We use microbes or products derived from them everyday., , •, , A common example is the production of curd from milk., , •, , Micro-organisms such as Lactobacillus and others commonly called lactic acid, bacteria (LAB) grow in milk and convert it to curd., , •, , Curd improves its nutritional quality by increasing vitamin B12 ., , •, , In our stomach, LAB play very beneficial role in checking disease-causing, microbes., , •, , The dough, which is used for making foods such as dosa and idli is also, fermented by bacteria., , •, , The puffed-up appearance of dough is due to the production of CO2 gas., , •, , The dough, which is used for making bread, is fermented using baker’s yeast, (Saccharomyces cerevisiae)., , •, , ‘Toddy’, a traditional drink of some parts of southern India is made by, fermenting sap from palms., , •, , The large holes in ‘Swiss cheese’ are due to production of a large amount of CO2, by a bacterium named Propionibacterium sharmanii., , •, , The ‘Roquefort cheese’ are ripened by growing a specific fungi on them, which, gives them a particular flavour., , Chemicals, Enzymes and other Bioactive Molecules, Examples of acid producers, , •, , Aspergillus niger (a fungus) produces citric acid,, , •, , Acetobacter aceti (a bacterium) produces acetic acid;, , •, , Clostridium butylicum (a bacterium) produces butyric acid and, , •, , Lactobacillus (a bacterium) produces lactic acid., , •, , Yeast (Saccharomyces cerevisiae) is used for commercial, production of ethanol., 1

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TLB’S Biology Classes, , Microbes used for production of enzymes, •, •, , Lipases are used in detergent formulations and are helpful in removing oily, stains from the laundry., Pectinases and Proteases are used for the preparation of bottled juices., , Streptokinase, •, , Streptokinase produced by the bacterium Streptococcus and modified by genetic, engineering is used as a ‘clot buster’ for removing clots from the blood vessels, of patients who have undergone myocardial infarction leading to heart attack., , Cyclosporin A, •, , The bioactive molecule, Cyclosporin A, is used as an immunosuppressive agent, in organ-transplant patients, is produced by the fungus Trichoderma, polysporum., , Statins, •, •, , Statins produced by the yeast Monascus purpureus have been commercialised as, blood-cholesterol lowering agents., It acts by competitively inhibiting the enzyme responsible for synthesis of, cholesterol., , 2

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TLB’S Biology Classes, , MICROBES AS BIOCONTROL AGENTS, Example of microbial biocontrol agentsBacillus thuringiensis, • An example of microbial biocontrol agents that can be introduced in, order to control butterfly caterpillars is the bacteria, Bacillus, thuringiensis (often written as Bt )., • These are available in sachets as dried spores which are mixed with, water and sprayed onto vulnerable plants such as brassicas and fruit, trees, where these are eaten by the insect larvae., • In the gut of the larvae, the toxin is released and the larvae get killed., • The bacterial disease will kill the caterpillars, but leave other insects, unharmed., • Because of the development of methods of genetic engineering in the, last, decade, or, so,, the, scientists, have, introduced, B. Thuringiensis toxin genes into plants., • Such plants are resistant to attack by insect pests., • Bt-cotton is one such example, which is being cultivated in some, states of our country., , 4

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TLB’S Biology Classes, , Trichoderma, • Trichoderma species are free-living fungi that are very common in, the root ecosystems., • They are effective biocontrol agents of several plant pathogens., , 5

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TLB’S BIOLOGY CLASSES, , BIODEVRSITY AND CONSERVATION, , Focus area-2022 Exam, , 1

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TLB’S BIOLOGY CLASSES, , PATTERNS OF BIODIVERSITY, Two patterns of biodiversity are present, I. Lattitudinal gradients, II. Species area relationship, , Explain species area relationship in biodiversity?,  The great German Naturalist and Geographer Alexander Von Humboldt, observed that within a region species richness increased with, increasing explored area, but only up to a limit.,  The relation between species richness and area for a wide variety of, taxa such as angiosperm plants, birds, bats, freshwater etc turns out to, be a rectangular hyperbola., ,  On a logarithmic scale, the relationship is a straight line described by, the equation,, Log S = log C + Z log A, Where,, , S = species richness, C = Y intercept, Z = slope of the line (regression coefficient), A = Area, , 2

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TLB’S BIOLOGY CLASSES, , What is the significance of the slope of regression coefficient in a, species area relationship?,  Ecologists have discovered that the value of Z lies in the range of 0.1 to, 0.2 regardless of the taxonomic group or the region.,  But, if we analyse the species area relationship among very large areas, like the entire continents, we will find the slope of the line to be much, steeper; that is Z values in the range of 0.6 to 1.2.,  For example, for frugivorous (fruit eating) birds and mammals in the, tropical forest of different continents, the slope is found to be 1.15., , LOSS OF BIODIVERSITY, What are the causes of biodiversity losses or species losses in a, geographical region ?, OR, what are “The Evil Quartlet”of biodiversity losses?, ,  The extinction species and consequent loss of biodiversity are due to, mainly four major reasons. They are known by the sobriquet “The Evil, Quartlet”, , 1. Habitat loss and fragmentation, 2. Over exploitation, 3. Alien species invasions, 4. Co-extinctions, , 3

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TLB’S BIOLOGY CLASSES, , 1. Habitat loss and fragmentation,  It is due to cutting down of trees, ploughing a grassland, filling a, wetland or burning a forest.,  The best example is the tropical rain forest. Once the forest covered, the 14% of earth’s land. Now it covers only 6%.,  The Amazonian rain forest, the lungs of the planet, harbouring, millions of species is being cut for cultivating soya beans or for, conversion to grasslands for raising beef cattle.,  The fragmentation of the forest i.e., broken down into small, fragments due to human activities also led to the disappearance of, many species., , 2. Over - exploitation, Humans have always depended on nature for food and shelter, but when, ‘need’ turns to ‘greed’, it leads to over -exploitation of natural resources., , Example,  The extinction of Steller’s sea cow and passenger pigeon were due, to over exploitation by humans., , 3. Alien species invasions, , • (Introduction of exotic species is one of the major threats to, biodiversity. Substantiate?),  New species entering a geographical region are known as exotic or, alien species.,  Introduction of alien species to a new habitat may adversely affect, the native species. Some time it may leads to the extinction of the, species., , Examples, •, , The Nile perch introduced into Lake Victoria in east Africa led to the, extinction of 200 species cichlid fish in the lake., , 4

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TLB’S BIOLOGY CLASSES, ,  Carrot, , grass, , (Parthenium),, , Lantana, , and, , water, , hyacinth, , (eicchornia) is also alien invasive species that destroyed the, environment.,  The introduction of African cat fish Clarias gariepinus for, aquaculture purpose is posing a threat to the native cat fishes., , 4. Co-extinctions,  When a species extinct, the animal or plant associated with it also, extinct. This is known as co-extinction., , Examples,  The extinction of a host fish leads to the extinction of parasites, associated with it,  In co evolved plant-pollinator mutualism extinction of one leads to, the extinction of the other., , BIODIVERSITY CONSERVATION, How do we conserve biodiversity?, Conservation of biodiversity can be done by two ways., , 1. In situ conservation(on site), 2. Ex situ conservation(off site), , 1. In situ conservation,  The conservation of genetic resources through their maintenance, within natural or even human made ecosystem in which they occur, is called in situ conservation., , , ‘biodiversity hotspots’ are the regions, , with very high levels of, , species richness and high degree of endemism.,  The species confined to a region and not found anywhere else are, known as endemic species., , , There are 34 biodiversity hotspots in the world., , 5

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TLB’S BIOLOGY CLASSES, ,  Three of these hotspots – Western Ghats and Sri Lanka, Indo-Burma, and Himalaya – cover our country’s exceptionally high biodiversity, regions.,  In India, ecologically unique and biodiversity-rich regions are legally, protected as biosphere reserves, national parks and sanctuaries.,  India now has 14 biosphere reserves, 90 national parks and 448, wildlife sanctuaries.,  Sacred groves are forests protected by tribal communities, which, are free from all disturbances. Tribal give religious sanctity to the, forest. The flora and fauna is well protected here.,  Sacred groves are found in Meghalaya, Rajasthan, Western Ghat, regions of Karnataka and Maharashtra and Madhya Pradesh.,  In Meghalaya, the sacred groves are the last refuges for a large, number of rare and threatened plants., , 2. Ex situ conservation,  In this approach, threatened animals and plants are taken out from, their natural habitat and placed in special setting where they can be, protected and given special care.,  Zoological parks, botanical gardens and wildlife safari parks,, Cryopreservation, Seed banks etc are examples for Ex situ, conservation.,  There are many animals that have become extinct in the wild but, continue to be maintained in zoological parks.,  Cryopreservation techniques are used for preserving gametes of, , threatened species in viable and fertile condition for long periods.,  Seed banks are used for preserving seeds of different genetic strains of, , commercially important plants for long periods., , 6