Chapter 4 Study guide Genetics Exam 2.docx

# Example 1 aa 2aa 1aa 1bb 2bb 1bb suppose you want to

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Example: (1 AA: 2Aa: 1aa) (1BB : 2Bb: 1bb) Suppose you want to know the proportion of A_B_ among the total progeny, you may first estimate which genotypes represent A_ and which genotypes represent B_. Clearly AA and Aa for the first genotype A_. And BB and Bb for the second genotype. From the above ratios in brackets or small Punnett squares: Ratio of A_ is the sum of the ratios of AA and Aa= 1/4+ 2/4= 3/4 Ratio of B_ is the sum of the ratios of BB and Bb =1/4+ 2/4= ¾ Therefore proportion of A_B_ is ¾ x ¾ =9/16. Similarly for others. 31. Given the molecular nature of a gene interaction (such as the chemical pathway in which the functional alleles of two genes (allele A, allele B) may be involved, be able to determine the phenotypes for particular genotypes. 32. Be able to name it as Recessive epistasis/dominant epistasis/ complementation epistasis/duplicate gene epistasis/ suppression epistasis. Be able to predict the final ratios for each phenotype. Be able to identify in words each form of epistasis when a statement is given. eg for recessive epistasis: when the recessive combination of alleles of one gene mask the phenotype associated with the alleles of a second gene

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eg. For dominant epistasis: When the presence of the dominant allele of one gene is able to mask the phenotype of the dominant allele of a second gene. et cetera. 33. Be able to define the term complementation (please refer text book). 34. Do epistasis results suggest the violation of Mendel’s law? Justify your answer. 35. In two gene interactions what property of the phenotypic ratios suggest that two genes are involved. 36. Given an example, be able to identify it as sex-limited inheritance. This means if the allelic combinations of a gene has two possible phenotypes, one phenotype is exclusively seen only in one of the two sexes whereas the second phenotype is present in both sexes depending upon the genotypes. 37. Given an example, be able to identify it as sex-influenced inheritance. In this case suppose the allelic combinations of a gene has two possible phenotypes and both these phenotypes are possible in both sexes for the appropriate genotypes. However for one sex, one allele behaves as a dominant allele whereas in the other sex the second allele behaves as a dominant allele. Therefore the heterozygote shows two different phenotypes in the two sexes. Explain what mechanisms may account for this difference?
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