0 1 pts Incorrect Question 13 You are studying a type of winged insect called a
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0 1 pts Incorrect Question 13 You are studying a type of winged insect called a spin fly (fictional). You don't know how sex is determined but you notice several traits that you can use to do crosses and if one of them is sex linked it will tell you whether the insects use the ZW or the XY system. All of your strains are pure-breeding. You cross female purple eyed spin flies to males with brown eyes and all the progeny have brown eyes. You do the reciprocal cross and all the progeny have brown eyes. What have you learned? The gene for purple vs brown eyes is on the Z chromosome with the allele for brown being dominant More than one of the other answers is correct Brown is dominant but you can't tell which chromosome it is on The gene for purple vs brown eyes is on the X chromosome with the allele for brown being dominant The gene for purple vs brown eyes is autosomal with the allele for brown being dominantExplanation / Answer
a) In the given question when a purple eyed female is crossed with male with brown eyes, all progeny has brown eyes. This can be represented as under:
Gene for Eye colour- Brown eyes B is dominant and purple eyes b is recessive
Pure bred individuals with brown eyes (BB) are crossed with pure bred individuals with purple eyes (bb)
In this case male has BB genotype and female has bb genotype
Their genes are crossed and we get heterogygous individuals with Bb genotype as shown in the Punnett’s square:
In the reciprocal cross all the progeny has brown eyes this is because in the given example of spin fly the gene for purple vs brown eyes is on Z chromosome with the allele for brown being dominant.
In the spin fly there is ZW system of sex determination. In contrast to XY and XO sex determination system where the sperm determines the sex in ZW system the ovum determines the sex of the offspring. Z chromosome is like the X chromosome of XY system being larger and with more genes. The males are homogametic sex (ZZ) and females are the heterogametic sex (ZW).
The ZW system of sex determination is found in birds, insects and some reptiles.
b) In the second cross which is also a monohybrid cross:
Male with CC genotype having straight wings is crossed with females having cc genotype and curled wings. We will get all the off springs as hybrid heterozygous Cc individuals having straight wings.
In the reciprocal cross that is male with curled wings crossed with females with straight wings, we get male offspring having straight wings and females having curled wings. This cross can be shown as below:
Female parent is heterozygous for the trait Cc having straight wings and male parent is homozygous for the trait cc having curled wings i.e,.
Bb * bb
This is because straight wing is dominant and the gene for wing shape is on Z chromosome.
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