PRINCIPLES OF INHERITANCE AND VARIATION
GENETICS Organisms reproduce- formation of offspring of the same kind. The resulting offspring most often do not totally resemble the parent. Branch of biology that deals with the in heritance and variation- Genetics. Inheritance- the process by which characters are passed on from parent to progeny Variation-it is the degree by which progeny differ from their parents. . .
HISTORY .Human knew before 8000- 1000 B. C variation is due to sexual reproduction .Exploited variations present in wild plants & animals to selectively breed & select organism with desirable characters Artificial selection & domestication of wild cow- Sahiwal cows in Punjab
TERMINOLOGY Genetics is the branch of life science that deals with the study of heredity and variation. Heredity is the transmission of characters from parents to their offsprings. . Variation is the difference among the offsprings and with their parents. Hereditary variations: These are genetical and inheritable. Environmental variation: These are acquired and non inheritable.
Gregor Johann Mendel: Father of Genetics Known as the father of modern genetics Gregor Mendel developed the principles of heredity while studying seven pairs of inherited characteristics in pea plants Although the significance of his work was not recognized during his lifetime, it has become the basis for the present-day field of genetics
MENDEL'S APPROACH Conducted hybridization (artificial pollination/ cross pollination) experiment for 7 years 1856-1863 & proposed law of inheritance Applied statistical analysis & mathematical logic for biology problems Large sampling size- greater credibility to data Experiments-true breeding pea lines (continuous self pollination) Confirmation of inference from experiments on successive generations of test plants, proved general rules of inheritance . . . Mendel investigated two opposing traits- tall & dwarf, yellow & green seed
Seven pair of contrasting characters selected by Mendel for his experiment. Seed Seed Seed Coat PodPodFlower Height Shape Color Color Shape Color Position Dominant Tl Round Yellow Greetd entulGreen Aial Recessive Trait Short Wrinkled reen White Consatcd Coiedlow Terminal flat)
TERMINOLOGIES Phenotype: The external appearance of an organism due to the influence of genes and environmental factors. . Genotype: The genetic constitution of an individual responsible for the phenotype Phenotypic ratio: The correct proportion of phenotype in population. Genotypic ratio: The correct proportion of genotype in population. Homozygous: The individual heaving identical genes in an allelic pair for a character. Ex: TT, tt. Heterozygous: The individual heaving un-identical genes in an allelic pair for a character. Ex: Tt. .
Dominant gene: The gene that expresses its character in heterozygous condition. Recessive: The gene that fails to express its character in heterozygous condition. Hybrid: The progeny obtained by crossing two parents that differ in characters. Back cross: The cross between F1 hybrid and one of its parents. Test cross: The cross between hybrid and its homozygous recessive parent. It is used to identify the genotype of the hybrid. . .
Why Mendel selected pea plant? Pure variety are available. Pea plants are easy to cultivate. Life cycle of plants are only few months. So that result can be got early. Contrasting trait are observed Flowers are bisexual and normally self pollinated Flowers can be cross pollinated only manually. Hybrids are fertile.
Parental Generation Gametes Tt F1 Generation Genotype Phenotype All are Tt All are tall (Mating) T t T t Gametes T T T t Tt T t F2 Generation Genotype Phenotype TT:Tt: tt= 1 : 2 : 1 Tall:Dwarf 3:1 T t T t