In Colias butterflies there is a rare allele which codes for an unusual stripe o
ID: 168092 • Letter: I
Question
In Colias butterflies there is a rare allele which codes for an unusual stripe on the forewing. The S allele acts as a dominant to produce the stripe but is a recessive lethal allele acting early in larval development. The gene is also located on the Z sex chromosome. (Remember, in butterflies females are the heterogametic sex.) Which of the following statements are true if a striped male and a normal female were crossed? Choose all that apply.
A) half of the male offspring would be striped
B) only males can be striped
C) the male parent must be heterozygous
D) half of the female offspring would be striped
E) there would be half as many female offspring as male offspring
Explanation / Answer
Conditions applied to this phenomenon:
A) half of the male offspring would be striped (In 2 males 1 is striped)
D) half of the female offspring would be striped (In 2 females 1 is striped)
Explanation:
According to the given question an unusual stripe is dominant (S), but a recessive lethal allele acting early in larval development. So the SS genotype is lethal.
Female is heterozygous (ZX) and Males are homozygous (ZZ)
Cross between the striped male and a normal female:
The genotype of striped male is SsZZ. It can produce 2 gametes called ( SZ, sZ)
The genotype of normal female = ssZX. It can produce 2 gametes called (sZ, sX)
Now a cross is taken placed between SsZZ X ssZZ can produce equal number of striped males and female. The number of stripe male and striped females are produced is equal to 1 each.
F1 phenotype and genotype ratio is 1 (SsZZ= striped male) : 1(SsZX= striped female) : 1(ssZZ= Normal male) : 1 (ssZx= Normal female).