What are the expected phenotypes from this pairing? (Sex-influenced Punnet Square)?
It turns out there is life on Mars, and genetics works the same way there. Tooth color is a sex-influenced trait in Martian rodents. Wild-type teeth are purple, and mutant teeth are green. The green allele is dominant in females and recessive in males. You have 2 rodents, a purple toothed male whose mother had green teeth, and a green-toothed female whose father had purple teeth. You mate them together. Calculate the probability that:
offspring would have purple teeth
offspring will be male, green teeth
offspring would be female, green teeth
I got 3/8, 2/8, 3/8 and I'm not sure if it's right. Thanks for the help in advance. 4/8, 2/8, and 2/8 wasn't the answer sadly. Here's the hint it gave me, hint: figure out the genotypes of the parents first. then write out the results of a cross between them, looking only at tooth color. then recall that for every baby rodent there is 1/2 chance it will be male and a 1/2 chance it will be female. finally, determine the phenotype for all offspring, male and female.
Glad I wasn't the one that was confused by the question though. only one* I tried out the question again, and I think you were right how 75% F would have green, and 75% M would have purple. It seems to be 4/8, 1/8, 3/8, because the fractions are representative of a male and female individual in each Punnet square. There's definitely a poorly worded question in this assignment, but this question was done in class with another example so I think I was just thinking about it wrong. Thanks for trying to help!
Answers
az_lender
For reasons of symmetry, the answers to the 2nd and 3rd questions should be the same.
However, the question really can't be answered without knowing the approximate frequency of each allele. For instance, the male's mother had green teeth, so we know she wasn't homozygous purple. But we don't know the probability that she was homozygous green (vs. heterozygous). Etc.
Anonymous
Are you sure that your instructor said that the "green allele is dominant in females and recessive in males"? I ask because the mechanism to accomplish that would be way too involved for an introductory undergraduate course in genetics. Calling purple wild and green mutant in such a scenario is pointless.
Anyway, my read is that the cross is Pp × Pp. (P being purple, p being green.) One could also do PG × PG.
You would then have to assume that martians have equal numbers of males and females.
Next you make the Punnet square, which ends up with 25% PP, 50% Pp and 25% pp offspring.
Next, you have to interpret the above genotypes through the lens of gender. The females will be 75% green, and the males 75% purple.
So I think it might be 4/8, 2/8, 2/8. But I am unsure.
Update: This question needs to be protested. If I was taking the course, I would begin by talking to the instructor, and requesting that it should not be included in students' grades.
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