Quantitative characters and Genes

Genes and quantitative characters,
Multiple factor hypothesis

1. Presented By… Maitri . M. Thakor M.Sc . (Botany) Department of life sciences, H.N.G.U., Patan . Genes & Quantitative Characters 1

2. Content Introduction Difference between qualitative & quantitative traits The multiple factor Hypothesis Some characters of quantitative traits ☻ Kernel colour in Wheat ☻ Skin colour in human ☻ Eye colour in human 2

3. Introduction Quantitative genetics have possibility of continuous variations. In 1760 , Joseph Kolreuter reported first case of continuous variation due to quantitative trait. Quantitative Characters are an inherited character that expressed phenotypically in all degrees of variation between one often indefinite extreme and another : a character determined by polygenes . 3

4. Difference – Qualitative & Quantitative Traits Qualitative Trait Quantitative Traits 1)Characters of kind. 2)Discontinuous variation; distinct phenotypic classes. 3)Single gene effect. 4)Concerned with individual matings & their progeny. 5)Analysed by making counts and ratios. 1)Characters of degree. 2) Continuous variations; phenotypic measure- ments from a spectrum. 3)Polygenic control; effects of single genes too slight to be detected. 4)Concerned with population of organisms consisting of all possible kinds of matings . 5) Statistical analyses. 4

5. Qualitative Trait Quantitative Trait (6) Ex.; Form (round/wrinkled seeds of pea), Structure ( horned /hornless conditions in cattle’s) Pigments (black/white coat of guinea pigs) Antigens & Antibodies etc. (6) Ex.; In human ( Skin colour, Eye colour, Hair colour, Weight, Height etc.) In plants (Seed colour in Wheat, Ear size in Maize, Corolla length in tobacco etc.) In animals (Size in chicken, Size in Rabbit, White spotting in mice etc.) etc. 5

6. The multiple factor hypothesis (concept) A gene, individually producing a slight effect on the phenotype but in combination with a few(2) or many other genes, controls as quantitative character is called as a Polygene . Since there are many genes of this kind for one quantitative character, they are also known as multiple factors , each factor having too small an effect to be traced. 6

7. Those genes(alleles) which contribute to the trait involved are called Contributing , effective or active genes(alleles). Those genes(alleles) which do not contribute to the trait involved are called non- contributing, non-effective or null genes(alleles). 7

8. Some characters of quantitative traits The inheritance of relatively simpler quantitative traits due to multiple factors of polygenes will be illustrated in this section with the help of three examples: (1) Kernel colour in Wheat (Studied by – H. Nilsson - Ehle ) (2) Skin colour in humans (Studied by – C. B. Devenport ) (3) Eye colour in human (Studied by – Burns & Battino-1989 ) 8

9. 1) Kernel colour in wheat A whole grain or seed of a cereal plant such as corn, wheat, barley, etc.. Is called Kernel. Kernel colour in wheat was studied by Swedish geneticist H. Nilsson – Ehle for the first time in 1908. P : Red kernel White kernel R 1 R 1 R 2 R 2 (Dominant) r 1 r 1 r 2 r 2 ( Recessive) R 1 R 2 r 1 r 2 F 1 : R 1 r 1 R 2 r 2 ( Light Red ) 9

10. F2 Generation : 10

11. Results: Genotype Genotypic ratio Number of Contributing alleles Phenotype Phenotypic ratio R1R1R2R2 1 4 Red 1 R1R1R2r2 2 3 Medium red R1r1R2R2 2 3 Medium red R1r1R2r2 4 2 Light red R1R1r2r2 1 2 Light red r1r1R2R2 1 2 Light red R1r1r2r2 2 1 Very light red r1r1R2r2 2 1 Very light red r1r1r2r2 1 White 1 cOlour red (15/16) Colourless (1/16) 4 6 4 11

12. 2) Skin colour in human This character was given by Davenport (1913) in Jamaica. He found that two pairs of genes, A-a and B-b cause the differences in skin pigmenta-tion between negro and Caucasian people. 12

13. P1: Negro White AABB aabb AB ab F1: AaBb Mulattoes- ( intermediate skin colour ) F2 generation : AB Ab aB ab AB AABB AABb AaBB AaBb Ab AABb Aabb AaBb Aabb aB AaBB AaBb aaBB aaBb ab AaBb Aabb aaBb aabb 13

14. Results: Phenotype Genotype Genotypic Frequency Ratio Negro(Black) AABB 1 1 Dark AaBB 2 Mulatto AABb 2 Mulatto AaBb 4 Mulatto aaBB 1 Mulatto Aabb 1 Light Aabb 2 Light aaBb 2 White aabb 1 1 4 4 6 14

15. 1 : 4 : 6 : 4 : 1 15

16. 3) Eye colour in human In human beings, the colour of eye is found to be determined by Polygenes. This genes have been suggested to be X-linked (see Burns and Battino, 1989 ). At least 9 classes of eye colour can be recognized in humans. In order of increasing amount of melanin pigmentation, these eye colours can be designated as light blue, medium blue, dark blue, grey, green, light brown, medium brown and dark brown. 16

17. Number of contributing alleles for each type of eye colour of human beings : Number of contributing alleles Eye colour Light blue 1 Medium blue 2 Dark blue 3 Grey 4 Green 5 Hazel 6 Light brown 7 Medium brown 8 Dark brown 17

18. Different eye colours found in human beings. 18

19. 1) Cell Biology, Genetics, Molecular Biology, Evolution and Ecology. Edition : 2008 Author : P. S. Varma, V.K. Agarwal. 2) Genetics Edition : 2011 (Fourth) Author : P. K. Gupta. 3) Genetics Editon : 2003 (First) Author : H.V. Bhaskar ; Suresh Kumar. 4) WWW.Slideshare.net References 19

20. 20