lo. Two points. Duplication of genes is an important evolutionary mechanism. As
ID: 270036 • Letter: L
Question
lo. Two points. Duplication of genes is an important evolutionary mechanism. As a result, many, cases are known in which a species has two or more identical genes a. Suppose there phenotype results only if an individual does not make any of that enzyme. needs to be functional in order to make the enzyme What ratio of normal to a result from a mating between two parents of genotype AaBb where A and B represent alleles that specify are two genes - A and B- that specify production of the same enzyme. An abnormal one of these two genes production of the enzyme, while a and b do not? Suppose now there are three genes specifying production of this enzyme and again that a single functional allele is sufficient for a wild-type phenotype. What ratio of normal vs, abnormal progeny would result?Explanation / Answer
16a) Answer: Ratio of normal to abnormal progeny is 15 : 1
AaBb x AaBb
Two genes : two set of alleles : 2n = 22 = 4 gametes from each parent = 16 possibilities
16b) Answer : Ratio of normal to abnormal progeny is 63 : 1
AaBbCc x AaBbCc
Three genes : three set of alleles : 2n = 23 = 8 gametes from each parent = 64 possibilities
Method :
Aa x Aa : 3/4 normal (AA or Aa) and 1/4 abnormal (aa)
Bb x Bb : 3/4 normal (BB or Bb) and 1/4 abnormal (bb)
Cc x Cc : 3/4 normal (CC or Cc) and 1/4 abnormal (cc)
Abnormal = 1/4 x 1/4 x 1/4 = 1/64
Therefore, 63/64 are normal and 1/64 is abnormal.
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