39. In a hypothetical population of deer, you learn that antler length maps to a
ID: 211790 • Letter: 3
Question
39. In a hypothetical population of deer, you learn that antler length maps to a single locus with two alleles (A, a). The A allele results in very large antlers and is completely dominant over a, which results in an absence of antlers. You genotype your herd and identify homozygous males and females. You cross a homozygous dominant male with a homozygous recessive females. The resultant offspring are then crossed to produce an F2 generation with the following results (yes, this is a crazy number of offspring, they are hypothetical deer) 247 males with no antlers 753 males with large antlers 1004 females with no antlers What is the inheritance pattern of this trait? Diagram the cross showing genotypes and phenotypes of both males and females for the parental generation F1, and F2 generation a. b.Explanation / Answer
a) The results of F1 progenies clearly suggest that it is a sex-limited inheritance. Sex-limited traits are expressed only in one sex although the trait is encoded in autosomal gene in both sexes.
b)Since it is a sex-limited inheritance, only male show the dominant phenotype of large antlers with 3:1 ratio. However the female does not show the large antlers even if it has dominant gene.
Genetic cross showing phenotype and genotype:
Homozygous dominant male (AA) with large antlers X Homozygous recessive female (aa) with no antlers
F1 progeny Heterozygous (Aa) (male with large antlers and female with no antlers)
F1 gametes: A, a
F2 progenies (F1 male X F1 female):
Gametes
A
a
A
AA
Large antlers male
No antlers female
Aa
Large antlers male
No antlers female
a
Aa
Large antlers male
No antlers female
aa
No antlers male
No antlers female
237 males with no antlers (genotype: aa)
753 males with large antlers (genotype: AA, Aa) (males follow 3:1 phenotypic ratio)
1004 females with no antlers (genotype AA, Aa, aa)
Gametes
A
a
A
AA
Large antlers male
No antlers female
Aa
Large antlers male
No antlers female
a
Aa
Large antlers male
No antlers female
aa
No antlers male
No antlers female
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