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Genes and Inheritance II Revision: most genes come in more than one form (alleles) New alleles are created by mutation and recombination Dominant and recessive.

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Presentation on theme: "Genes and Inheritance II Revision: most genes come in more than one form (alleles) New alleles are created by mutation and recombination Dominant and recessive."— Presentation transcript:

1 Genes and Inheritance II Revision: most genes come in more than one form (alleles) New alleles are created by mutation and recombination Dominant and recessive properties of an allele determine its effect on the phenotype Its not always that simple though

2 Inheritance in families Many traits can be followed in families (pedigree analysis) There are many examples, including some human diseases and other conditions Careful study of the pedigree shows the mode of inheritance (dominant, recessive) See examples in textbook: figures and 10.11

3 Multiple alleles A gene can have more than 2 alleles Levels of dominance are possible Figure – coat colour in rabbits There is a hierarchy of dominance leading to several different coat colours

4 Dominance of alleles: C > c ch > c h > c Sable Chinchilla Iron grey Himalayan White Thanks to Lauren Spence for the photos

5 Incomplete dominance Many alleles are not completely dominant or recessive - their effects blend together or mix Example - the colours of snap-dragon flowers (red/pink/white) The inheritance still follows Mendels laws Figure in textbook

6 Co-dominance Co-dominant alleles are ones whose effects can both be seen together in the phenotype A good example is the human ABO blood group system This has 3 alleles, I A, I B, I O Their presence in a persons blood can be detected using specific antibodies Figure in textbook

7 Interactions between genes Epistasis is where genes alter the effects of other genes This is also very common An example is mouse coat colours (figure 10.15) Wild-type is agouti (dominant allele B) with bands on the hairs, mouse is grey bb genotype has no bands on hairs and is black A second gene (A,a) affects pigment production Homozygous aa mice are albino (no pigment is produced) so effect of B,b gene cannot be seen Aa and AA produce pigment so effect of B,b gene is seen

8 Epistasis - mice coat colours Agouti (wild-type) Albino (aa) Black (bb, not aa)

9 Polygenic inheritance Many traits are influenced by several genes together (polygenes) Includes human traits like height, skin colour - these are continuous traits (there is a spectrum of values between the 2 extremes) Probability applies here as well - this is why most individuals are about average with few at the extremes - figure (different in Purves 7 th edition)

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11 Gene-environment interaction Many genes influence the phenotype in a way modified by the environment Siamese cats again! Pigment produced because enzyme active in cool parts of body If you remove some dark fur then put the cat in a warm environment, fur grows back light-coloured The proportion of individuals carrying the gene that actually show the phenotype is called the penetrance


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