UNIT I Classical genetics Mendels law Gene interaction Co dominance Supplementary Complementary Dominant Epistasis Pleiotrophism Penetrance ID: 1046364
Download Presentation The PPT/PDF document "GENETICS CORE COURSE III – ..." is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
1. GENETICS
2. CORE COURSE III – GENETICS UNIT - IClassical genetics: Mendels law - Gene interaction: Co dominance, Supplementary, Complementary, Dominant Epistasis, Pleiotrophism, Penetrance, Expressivity - Sex linked Inheritance in man, Sex influenced genes, Sex limited genes - Genomic imprinting, X inactivation in mammals .
3. Genetics is the science of heredity. It deals with the study of charaters and their transmission from the parents to the youngones.Heredity refers to passing of physical and mental characteristics from parents to children.John Gregor Mendel is the father of genetics.
4. Monohybrid experimentThe crossing of two plants differing in one character is called Mono hybrid experiment.Mendel carried out monohybrid experiments on pea plants for all the seven pairs of characters independently and based on the results of monohybrid experiment, he formulated the law of segregation.Mendel selected two plants, one plant is tall stem and other plant is short stem or dwarf.
5. The plants are considered as parental plants (P). It is pure breeding. tall and dwarf plants were crossed.Seeds were collected from these plants.These seeds were sown in garden and a group of plants were raised. The plants constituted the first filial generation or F1 generation.All the F1 plants were tall.The F1 plants were inbred.
6. The seeds were collected and sown in garden and a group of plants were raised. The plants constituted the F2 generation.In the F2 generation, tall and dwarf plants were found.Mendel counted the number of tall and dwarf plants.Of the 1064 plants of F2 generation, 787 plants were tall and 277 plants were dwarf, ie., 75% were tall plants and 25% were dwarf plants.thus the ratio of tall and dwarf plants were 3:1.
7. The pure tall parent has two dominant genes (TT). The pure dwarf parent has two recessive genes (tt).During gametes formation, the two genes separate and enter different gametes.Hence each gamete will contain only one gene.The gametes produced by tall parent contains T and dwarf parent contains t.
8. When these two parents (tall and dwarf) are crossed, the “T” gene carrying gamete fuses with “t” gene carrying gamete. When seeds were formed. The seeds were sown. The F1 generation plants were tall. They contain Tt genes. In the plants, the dominant gene T masks the expression of the recessive gene t.
9. The F1 plants (Tt) produce two types of gametes; some gametes receive the dominant gene T (50%)and others receive the recessive gene t (50%). F1 plant was self fertilized.These male and female gametes unite to form seeds. From the seeds, F2 generation plants (four)were raised. Where 75% plants were tall and 25% plants were dwarf.They have TT, Tt, Tt and tt genes. The phenotypic ratio is 3:1 and the genotypic ratio is 1:2:1.It is clearly understood by gametes are placed in Checker Board or Punnet square.
10. Parents: Male female Tall Dwarf TT ttGametes : T t F1 Generation: Tall F1 plants are crossed Tt × Tt Gametes : F2 : TT Tt Tt tt Tall Tall Tall Dwarf 75% 25% 3 1 TtTtTt
11. GAMETESTTTtTtttTtTt
12. Phenotypic ratio: 3:1 (Tall:Dwarf)Genotypic ratio: 1:2:1
13. Dihybrid experimentThe crossing of two plants differing in two characters is called dihybrid experiment.Parents: Yellow Round × Green wrinkled YYRR yyrrGametes: YR yrF1: YyRr Yellow RoundF1 plants are crossed: YyRr × YyRrGametes: YR Yr yR yr YR Yr yR yr
14. GametesYYRRYellow Round YYRrYellow RoundYyRRYellow RoundYyRrYellow RoundYYRrYellow Round YyrrYellow wrinkledYyRrYellow RoundYyrrYellow wrinkledYyRRYellow RoundYrRrYellow RoundyyRRGreen RoundyyRrGreen RoundYyRrYellow RoundYyrrYellow wrinkledyyRrGreen RoundyyrrGreen wrinkledYRYryRyrYRYryRyr
15. F2 Phenotypic ratio is 9:3:3:1Yellow Round : 9Yellow Wrinkled: 3Green Round : 3Green wrinkled : 1
16. Mendel’s lawsBased on Mendel’s experimental results certain principles are framed. These principles are called Mendel’s laws. They are as follows:1. Law of Dominance2. Law of segregation or law of purity of gametes3. Law of independent assortment
17. 1.Law of dominance “One factor in a pair may mask or prevent the expression of the other”.- The law formulated based on the mono hybrid experiment.
18. 2. Law of Segregation “During gamete formation the genes of a particular character separate and enter different gametes”.This is also called law of purity of gametes.This law is also formulated based on mono hybrid experiment.
19. 3. Law of Independent AssortmentThis law is based on dihybrid experiment.“The genes for each pair of character seperate independently from those of other characters during gamete formation”.