Page 1 :
Mendelian Disorders, In humans, Mendelian disorder is a type of genetic disorder primarily resulting due to alterations in one gene, or as a result of abnormalities in the genome. Such a condition can be seen since birth and be deduced on the, basis of family history using the family tree. The analysis hence carried out is known as pedigree analysis., These genetic disorders are quite rare and may affect one person in every thousand or a million. Genetic, disorders may or may not be inherited. Inheritable genetic disorders usually occur in the germline cells,, whereas in non-inheritable genetic disorders the defects are generally caused by new mutations or due to, some changes in the DNA. For instance, cancer may either be caused by an inherited genetic condition, or by a, new mutation caused by the environmental causes or otherwise., Types of Mendelian Genetic disorders, According to Mendel’s’ laws of inheritance, the different types of Mendelian disorders include:, 1., 2., 3., 4., 5., , Autosomal dominant., Autosomal recessive., Sex-linked dominant., Sex-linked recessive., Mitochondrial., , The various types of Mendelian disorders can be identified easily from the pedigree analysis., Examples of Mendelian Disorders, •, , Sickle cell anaemia, , •, , Muscular dystrophy, , •, , Cystic fibrosis, , •, , Thalassemia, , •, , Phenylketonuria, , •, , Colour blindness, , •, , Skeletal dysplasia, , •, , Haemophilia, , Haemophilia, •, •, •, , •, , This is a type of sex-linked recessive disorders. According to the genetic inheritance pattern, the, unaffected carrier mother passes on the haemophilic genes to sons., It is a very rare type of disease among females because for a female to get the disease, the mother, should either be hemophilic or a carrier but the father should be haemophilic., This is a disorder in which blood doesn’t clot normally as the protein which helps in clotting of blood is, affected. Therefore, a person suffering from this disease usually has symptoms of unexplained and, excessive bleeding from cuts or injuries., This type of genetic disorder is caused when the affected gene is located on the X chromosomes., Therefore, males are more frequently affected., , Sickle-cell anaemia, •, •, , This is a type of autosomal recessive genetic disorder., According to Mendelian genetics, its inheritance pattern follows inheritance from two carrying, parents.

Page 2 :
•, , •, , It is caused when the glutamic acid in the sixth position of the beta-globin chain of haemoglobin, molecule is replaced by valine. The mutant haemoglobin molecule undergoes a physical change which, changes the biconcave shape into the sickle shape., This reduces the oxygen-binding capacity of the haemoglobin molecule., , Phenylketonuria, •, •, •, , This genetic disorder is autosomal recessive in nature., It is an inborn error caused due to the decreased metabolism level of the amino acid phenylalanine., In this disorder, the affected person does not have the enzyme that converts phenylalanine to, tyrosine. As a result, phenylalanine accumulation takes place in the body and is converted into many, derivatives which result in mental retardation., , Thalassemia, •, •, •, , This is a type of disorder in which the body makes an abnormal amount of haemoglobin. As a result, a, large number of red blood cells are destroyed that leads to anaemia., It is an autosomal recessive disease., Facial bone deformities, abdominal swelling, dark urine are some of the symptoms of thalassemia., , Cystic Fibrosis, •, •, •, , This is an autosomal recessive disorder., This disease affects the lungs and the digestive system and the body produces thick and sticky mucus, that blocks the lungs and pancreas., People suffering from this disorder have a very short life-span., , Disorders of a chromosomal nature include:, 1., 2., 3., , Down’s syndrome., Klinefelter’s Syndrome., Turners Syndrome., , Down’s Syndrome: Down syndrome is a genetic disorder, which leads to various physical and mental, disabilities. It is due to the presence of an extra chromosome 21 also known as trisomy of chromosome 21., Down syndrome is one of the leading causes of genetic disorders around the world., ▫, ▫, , ▫, ▫, ▫, , ▫, , ▫, , It is named after the physician Langdon Down, who first observed this condition., Other than physical attributes and mental retardness, they are also susceptible to various diseases, like leukaemia and Alzheimer’s. There is no cure, only the quality of life can be improved by taking, extra care and training the individual to perform daily essential activities. Down syndrome can be, diagnosed during early screening in pregnancy, which can decrease the occurrence of disease., Down syndrome is a chromosomal disorder. It is due to aneuploidy of the autosome. There is one, extra chromosome 21 or part of the chromosome present in all the cells or some cells., The occurrence of Down syndrome is 1:800 live births. The major risk factor is the age of the mother., Most of the trisomy cases occur in the mother having age more than 35., Down syndrome is caused due to abnormal cell division. During mitotic and meiotic cell division the, chromosome pair separate so that each cell gets a copy of each chromosome. In down syndrome, the, chromosomes are not able to separate, giving rise to cells with an unequal number of chromosomes., This phenomenon is called nondisjunction., Nondisjunction happens, when chromosome segregates in anaphase before all of the replicated, chromosomes’ kinetochores are attached to microtubules from opposite poles during metaphase. It, results in one daughter cell having one less chromosome and another with one extra chromosome., The life span of an individual with Down syndrome is around 60 years, it depends on the number of, health complications present.

Page 3 :
The main symptoms of Down syndrome are:, 1., 2., 3., 4., 5., 6., 7., 8., 9., 10., , Short stature and stunted growth, Fold of the skin above the eye, slanted eyes, Protruding furrowed tongue, flattened nose, Mental retardation, Cardiac deformities, Single transverse palm crease and hand is broad and short, Poor muscle tone and excessive flexibility, Small head, short neck and abnormal teeth, Delay in language development, Cognitive impairment may be mild to moderate, , Turner’s Syndrome: Turner syndrome is a genetic disorder in females, it is due to the partial or complete loss, of one of the X chromosomes. Turner syndrome is also known as monosomy of the X chromosome. Turner, syndrome leads to various developmental problems and people with Turner syndrome are at risk of many, diseases., ▫, ▫, ▫, , ▫, , ▫, ▫, ▫, , In 1938, Henry H. Turner described the condition first hence the name Turner syndrome., Turner syndrome is the only viable monosomic chromosomal anomaly., Turner syndrome causes retarded sexual development in females. They are mostly sterile with short, stature and webbing of the skin in the neck region is present. Apart from these, there may be cardiac, abnormalities, hearing impairment, vision loss, etc. may be present in a person with Turner, Syndrome., There is no cure because it is a genetic disorder, but treatment may help in resolving issues such as, learning difficulties, short stature and sexual development. Turner syndrome can be diagnosed by, antenatal tests during pregnancy., Only females are born with this condition., The occurrence of Turner syndrome is 1:2500 female births., Monosomy of X: This accounts for half of the Turner syndrome cases. There is a complete loss of one, X chromosome. This results from the abnormal cell division during gamete formation. Eggs or sperm, lack a sex chromosome. People with this type of Turner syndrome have all the cells lacking one X, chromosome, i.e. they have 45 chromosomes in all the cells. People with XO are found to have no, Barr bodies, i.e. the X chromosome present is not inactivated but the active genes are required in pair, for proper growth and development., , Main symptoms of Turner syndrome include:, , 1., , Common facial features such as drooping eyelids, narrow palate, small jaws and low-set prominent, earlobes, 2. Growth is irregular, no regular growth spurts and puberty is delayed, 3. Short stature as compared to other females, 4. Female may have normal intelligence and good reading and verbal skills but may have some learning, difficulties, e.g. difficulty in memorising, difficulties in learning math and spatial concepts, 5. They might find difficulty in non-verbal communication and understanding of other’s emotions, 6. Poorly developed breasts, delayed or no onset of the menstrual cycle and infertile, 7. Murmuring of heart due to narrowing aorta and other abnormalities related to heart, liver and kidney, 8. Hypothyroidism and hypertension is frequent, 9. Insufficient estrogen leads to osteoporosis, 10. Chronic middle ear infection leading to hearing loss, Symptoms of Turner syndrome can be seen in the developing foetus also:, 1., , Lymphedema is characterised by swelling due to excess fluid leaking in the body

Page 4 :
2., 3., , Swelling or thickness of the neck, Lower than normal weight, , Klinefelter Syndrome: The Klinefelter syndrome definition says that Klinefelter syndrome is a disorder, commonly found in men. This syndrome is caused when a baby of the male sex has taken birth with an excess, of X chromosomes that needed., ▫, , ▫, , ▫, , ▫, , ▫, , ▫, ▫, , This syndrome usually only occurs in 1 out of 1000 males. The addition of the undesired X, chromosomes is generally caused by an accidental blunder caused in the development of the egg or, the sperm., This presence of excess X chromosomes within a male occurs when there is an uneven distribution of, the genetic material within the egg. The same can also happen within a sperm. Even though this is a, genetic disorder, unlike many other genetic disorders, this does not pass down to other family, members., Even while looking at a male who is suffering from the Klinefelter syndrome, you may not observe any, such symptoms which might distinguish him; there are some symptoms that set them apart. For, example- erratic and sparse distribution of hair all across the body, broad and wider hips, and you, may also notice an amplified breast size. The testicles also remain small, and in some, the penis may, not see an increase and transition to the adult size., When a male baby or toddler is suffering from the Klinefelter disorder, unlike the other babies, they, take a longer time to learn how to walk, talk, sit, crawl. They are way calmer, quieter than babies, should normally be., During the growing up period, they may suffer from phases of doubting their self-esteem and being, under-confident. They may be extremely passive and shy and have problems in understanding and, comprehending words, which leads to reading, writing, and spelling problems., They could show similar symptoms to that of dyslexia or dyspraxia. In the adolescent period, they may, be way taller than usual., They may have extremely long arms, wide hips, poor muscle growth, scanty body hair, an unusually, small penis, and testicles and amplified breast size. When they grow into adults, they have poor, fertility and are not very sexually active.