Page 1 :
i, ', , , , , , , , CHAPTER-09 HEREDITY AND EVOLUTION, , Subject -Biology Class - Xth By- Aryan sagar, , > Heredity- The transmission of genetic characters from parents to offspring or one generation to next, is called heredity., , > Inheritance- The process by which genetic traits are passed from one generation to the next is called, inheritance., It is also called the phenomenon of “Like begets like” ., , > Variations- The differences in traits of individuals of a progeny from each other and from their, parents are called variations., , > Genetics- The branch of biology which deals with heredity and variation is called genetics., The term genetics was given by Bateson in 1906., , > Offspring- The individuals formed by sexual reproduction are called offspring. :, , > Clone-The group of individuals having the same genotype is called clone and the members a clone is, , ~ called ramets , MENDEL 3—>, , Gregor Johann Mendel (1822-1884) is known as Father of Genetics .Because he discovered, , the mechanism of transmission of characters from one generation to the next., , > He was born ina poor farmer family of village silician 6f heinzendorf »Moravia (Austria),on July 22,, 1822. He received early education at home and in a preparatory school and he was a brilliant, student and studied philosophy for several years., , > After schooling, Mendel joined monastery of St.Thomas in Brunn at the age of 21 in 1843. He became, priest in 1847and in 1851 Mendel went to university of viena for study of science and Mathematics., , -> He returned Brunn as assistant teacher and serves as teacher for 14years.In1868 Mendel was made, , abbot of his monastery . He died in 6 jan 1884 due to chronic nephritis., , Vv, , Mendel Experiments:, > He performed his first experiment on hybridisation of pea plant in 1856. He continued his ., , hybridisation experiments on for seven years from 1856 to 1863., , Mendel performed cross breeding and self breeding in different varieties. He read out the results of, , his experiments at two meeting of natural history society of Brunn in 1865., , His paper was “Experiments on plant hybridisation “was published in the proceeding and the society, , in 1866. :, , > Experiments remain unnoticed for 34 years from publishing and 16 years from his death due to, scientific world in Darwin theory of natural selection., , > Mendel’s experimental material:, ‘> Mendel selected garden pea plant (Pisum sativum) as his experimental material because of the, following reasons:— :, , > It is annual plant with a short life cycle., , > Ithas perfect bisexual flower containing male and female parts., , > The flower are predominantly self-pollinating, i.e, cleistogamous., , >, , >, , v, , v, , It is easy to grown, handled and sharply shows his characters., Pea plants produce a large numbers of seeds in one generation., , Mendel’s Observations

Page 2 :
Mendel observes seven contras, picked up 34 varieties for his ex;, , These are as follows:, , , ting characters of pea plant In seven years between 1856-1863,He, . periments and the number was reduced to 22 and finally 7. All he +, seven varieties had least one character with two contrasting tralts., , , , CHARACTERS, , , , DOMINANT TRAIT, , Récessive TRAIT, , , , Seed Shape. ‘, , Raina,, , , , Seer coloty +, , Yellos)., , tvinkledl, , Green, , , , , , , , Violet, , , , , , , , , , , , , , , , , , , , , , , , aa, , , , Character-it is a distinct morphological and Physiological feature fo an individual, e.g stem height, flower colour, position of flower, shape of seed,etc, Trait- It is an expression of a character like tallness, dwarfness, Position curly or straight hair., , Unit Factor-it is (tis a Particulate entity that function as a unit of inheritance Passing from generation, to generation and controlling expression of a character., , The unit factor has been called gene by Johannsen in 1909.Gene is the small segment of DNA., Alleles-They are various form of a gene which occurs at the same place or gene locus over, chromosomes. e.g-TT,Tt,tt., , Symbols-Each gene or its character is given a symbol generally in the form of a capital letter for the, dominant trait and small alphabet for the recessive trait.e.g-TT (tall), tt dwarfness., , Phenotype-tt is the observable characters of an individual.eg-tall, dwarf, , Geneotype-tt is a gene complement of an individual,with regard to one or more characters.e.g-TT,Tt,, tt., , Heterozygous /Hybrid-An individual having both the contrasting alleles of a character is called, hybrid or heterozygous individual, e.g Tt., , Dominant trait-it is a factor or allele which can express its effect whether present in homozygous, factor or heterozygous state, e.g T (in TT, Tt,)., , Recessive trait-The factor or allele which is unable to express its effect in the presence fo contrasting, factor ir called recessive trait.eg -t, , F1 Generation (First Filial Generation) -It is the generation of hybrids produced from a cross between, genetically different individuals called parents., , F2 Generation-(second filial generation) It is the generation of individuals which develops as a result, of selfing of F1 progeny., , Monohybrid Ratio-It is ration which is obtained in F2generation when a monohybrid cross is made, by seifing between F1 progeny., , Dihybrid Ratio- It is ratio which is obtained in F2 generation when a dihybrid cross is made by selfing, between F1 progeny. ., , Punnet Square-It Is a checker board or square divided into smaller Squares where gll the possible, types of gametes are shown male in horizontal row and female in vertical column., , The checker board was first devised by Punnet in 1927 and is known as Punnet square., , True Breeding-They are homozygous or genetically pure individuals which produce similar offspring., Astrain of true breeding individuals is called pure line., , Back Cross-It is a cross between the hybrid and one of its parents which can be repeated two or more, times for obtaining the maximum number of traits of that parent.