1. ( 10 points ) You are studying wing colour in a newly discovered type of butt
ID: 190041 • Letter: 1
Question
1. (10 points) You are studying wing colour in a newly discovered type of butterfly. The ZW system is used in butterflies, where males are Z/Z and females are Z/W. You have two different populations of pure-breeding butterflies. One population has orange and black wings and the other has solid orange wings.
b) What does pure-breeding mean? (1 point)
You do a pair of reciprocal crosses with your two populations. CROSS A involves black and orange females crossed to solid orange males. All the F1 offspring of cross A have solid orange wings.
c) What have you learned from this cross? (1 point)
CROSS B involves a solid orange winged female and a black and orange male.
d) Predict the outcome expected if the wing colour trait is sex-linked. Use defined symbols of your choice in your explanation. (2 points)
e) Predict the outcome expected if the wing colour trait is autosomal. Use defined symbols of your own choice (2 points)
f) If the trait is sex-linked, predict the offspring expected if the F1 from cross B (described in part d, above) are interbred. (2 points)
Explanation / Answer
1 b). Pure breeding means that the parental generation is homozygous for the trait being considered and the offspring will therefore take up the parental phenotypes.
c) Since this is pure breeding line, therefore the reciprocal cross would be between homozygous recessive and dominant and the trait that shows up will be dominant. We have learned that Solid orange wing is the dominant phenotype and the allelle for this is dominant while black and orange wing is a recessive trait.
d) Now sex-link can be Z-linked or W-link. The males (ZZ) in cross A had solid orange wings which means the trait is not W-linked.It is Z-linked. Therefore, the female will be ZA W and male will be Za Za. The offsprings will therefore be: Males- ZA Za (Solid orange wings) and Female- Za W (black and orange wings).
e. If the trait is autosomal then all the progeny will have the dominant phenotype, Solid orange wings as the genotype will be Aa.
f. If ZA Za (Solid orange wings) is crossed with Za W (black and orange wings) considering it to be sex-linked trait, then the prgeny will be Male: ZA Za (Solid orange wings) , Za Za (black and orange wings), and female: ZA W (Solid orange wings), Za W (black and orange wings) in the phenotypic ratio 1:1:1:1.
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