Question

In: Biology

a) Color blindness is an X-linked trait. A female who is color blind marries a male...

a) Color blindness is an X-linked trait. A female who is color blind marries a male with no history of the condition.   Show the problem. Of their children, what proportion would be expected to be color blind? Are these sons or daughters or both? Are any children carriers (having the gene, but not expressing the condition)? Are these sons or daughters or both?

b)In sea horses long tail is dominant to short, and thick scales is dominant to thin. Cross two seahorses that are heterozygous for both traits. What are the expected genotypic and phenotypic ratios in the F1?

c) A female with type A- blood marries a male with type AB+ blood. The female is heterozygous for blood type (codominant trait). The male is heterozygous for Rh factor (treat as complete dominance). Show the problem. What are the expected genotypic and phenotypic ratios in their offspring? [problem is a dihybrid cross of a codominant trait and a complete dominant trait]

Solutions

Expert Solution

a. XC = WT dominant allele
Xc = Mutant recessive allele

Female = XcXc
Male = XCY

Parental cross: XcXc X XCY
Progeny:
XCXc = Carrier female
XcY = Affected male

b. Long tail = Dominant = L
Short tail = Recessive = l

Thick scales = Dominant = T
Thin scales = Recessive = t

Parental cross: LlTt X LlTt
Progeny:
Phenotypic ratio = 9:3:3:1
Genotypic ratio = 1:1:1:1:2:2:2:2:4

L_T_ = 9/16 = Long tails and thick scales
L_tt = 3/16 = Long tails and thin scales
llT_ = 3/16 = Short tails and thick scales
lltt = 1/16 = Short tails and thin scales

See image for the punnet square



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