The a allele of a locus determining body size is a recessive, lethal and sex-lin
ID: 69837 • Letter: T
Question
The a allele of a locus determining body size is a recessive, lethal and sex-linked trait. The a allele promotes a medium body size through incomplete dominance with the A allele. Individuals with the AA genotype have very large size. A separate autosomal locus exhibits recessive epistasis to the lethality of the a allele . At this autosomal locus, the B allele is dominant to the b allele to determine a black coat color as opposed to a brown coat.If a rabbit with a medium body size and black coat (heterozygous) is mated witha male with a very small body size and a brown coat, how many offspring of 30 would have a very small body size?
My work:
Body size:
XAXA - > large
XAXa -> medium
XaXa - > very small
Coat Color:
BB - > black
Bb - > black
bb - > brown
Cross:
black coat (hetero) medium sized female x brown coat and very small male
XAXaBb x XaYbb
XAxa -> 0.25 Bb -> 0.50
xaxa -> 0.25 bb -> 0.50
xAy -> 0.25
XaY -> 0.25
Explanation / Answer
Genotype of female: XAXaBb
Genotype of male: XaYbb
Xab
Xab
Yb
Yb
XAB
XAB Xab
XAB Xab
XAB Yb
XAB Yb
XAb
XAb Xab
XAb Xab
XAb Yb
XAb Yb
XaB
XaB Xab
(small body)
XaB Xab
(small body)
XaB Yb
(small body)
XaB Yb
(small body)
Xab
Xab Xab
(small body)
Xab Xab
(small body)
Xab Yb
(small body)
Xab Yb
(small body)
As you can see, total offsprings having small body = 8 / 16 = 0.5 = 50 %
So, out of 30 there will 15 offsprings which will have small body.
Xab
Xab
Yb
Yb
XAB
XAB Xab
XAB Xab
XAB Yb
XAB Yb
XAb
XAb Xab
XAb Xab
XAb Yb
XAb Yb
XaB
XaB Xab
(small body)
XaB Xab
(small body)
XaB Yb
(small body)
XaB Yb
(small body)
Xab
Xab Xab
(small body)
Xab Xab
(small body)
Xab Yb
(small body)
Xab Yb
(small body)
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