Recombination Frequency Recitation Investigators mated a testcross male with a f
ID: 220781 • Letter: R
Question
Recombination Frequency Recitation
Investigators mated a testcross male with a female that was heterozygous at two separate genetic loci – the smooth abdomen (sa) and the straw body (sb) loci. Both of these phenotypes are inherited in an autosomal recessive pattern. The following phenotypes were observed in the progeny:
Genotype
Number of Progeny
Wild type abdomen, wild type body
426
Smooth abdomen, wild type body
67
Wild type abdomen, Straw body
73
Smooth abdomen and straw body
434
A. Write the phenotypes for each allele.
B. Write the genotypes of the parents
C. Draw a Punnett square of the cross. Write the predicted phenotypic ratio.
D. Are the two genes (sa and sb) linked? If no, explain how you know this. If yes, how far apart are the sa and sb genes? Show your work for full credit
Genotype
Number of Progeny
Wild type abdomen, wild type body
426
Smooth abdomen, wild type body
67
Wild type abdomen, Straw body
73
Smooth abdomen and straw body
434
Explanation / Answer
A. The phenotypes for each allele is as follows
sa - smooth abdomen
sb - straw body
SA - wild type abdomen
SB - wild type body
B. Genotypes of the parents are
SBSA x sasb
C. Punnet square of the cross is
SB SA sa sb
SB SBSB SBSA SBsa SBsb
SA SBSA SASA SAsa SAsb
sa SBsa SAsa sasa sbsa
sb SBsb SAsb sbsa sbsb
The predicted phenotypic ration will be 9:3:3:1
D. Both the genes sa and sb are linked. Thats why there are more number progeny with smooth abdomen and straw body.
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