Finger length is genetically variable in humans, and sex influenced. One autosom
ID: 48759 • Letter: F
Question
Finger length is genetically variable in humans, and sex influenced. One autosomal (fully penetrant) gene appears to control the relative lengths of the second and fourth digits. The S allele is associated with the second digit being shorter than the fourth, and the L allele is associated with the second digit being longer than (or as long as) the fourth.
Matings of SL heterozygotes (SL X SL) produce females with the short and long phenotypes in a ratio of 1 to 3, and males with short and long phenotypes in a ratio of 3 to 1.
What are the likely genotypes, associated phenotypes, and their ratios in the two sexes.
Genotypes
Ratios
Phenotypes
males
females
Given the cross SL X LL. Based on your answer to a) what are the likely genotypes, associated phenotypes, and their ratios in the two sexes.
Genotypes
Ratios
Phenotypes
males
females
Genotypes
Ratios
Phenotypes
males
females
Explanation / Answer
As the alleles are sex influenced S allele is dominant in females and recessive in males. L allele is recessive in males and dominant in females.
When mating of SL heterozygotes occur. then
Genotypes
Ratio
Phenotypes
Males
Females
SS
1/4
Short
Short
SL
1/2
Short
Long
LL
1/4
Long
Long
When the cross SL X LL occurs, then
Genotypes
Ratio
Phenotypes
Males
Females
SL
1/2
Short
Long
LL
1/2
Long
Long
Genotypes
Ratio
Phenotypes
Males
Females
SS
1/4
Short
Short
SL
1/2
Short
Long
LL
1/4
Long
Long
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