Genetics as it applies to evolution, molecular biology, and medical aspects.
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"In guinea pigs (Males XY and Females XX), a series of mating between albino females (all the same genotype) and grey males (all the same genotype) produced the following results: 101 albino males (24 of the 101 died at birth), 26 black females, 48 grey females, and 27 cream females (all 27 died at birth)."
The question continues, but I am stuck in determining the genotypes of the parents and the progeny in this case. I am assuming that we are dealing with two genes, and that one is autosomal and one is sex-linked. I realize that approx. one quarter of the males produced and one quarter of the females produced die. But why are there no grey males or albino females in the progeny when those are the phenotypes of the parents? How can there be 4 phenotypes of females and only 2 types for males?
Without determining the initial genotypes, I cannot compete the rest of the question.
Thank you for your help!
You're right to assume you have one sex-linked gene and one autosomal gene. All of the male progeny being albino while all of the female parents were albino though none of the female children are albino suggests that there is a gene on the X chromosome which is recessive, and having only the recessive copies will make the guinea pig albino. The female parents had two copies (one on each X chromosome) (X^a,X^a) while the males have a dominant gene that allows them color (X^A,Y). All the male children end up with (X^a,Y) so are albino, and all the female children end up with (X^A,X^a) so have pigmentation. The other autosomal gene (C), has a lethal recessive allele. All parents were Cc for this allele, which is why the progeny were in the 1:2:1 ratios (though this was only seen with the females because males had color knocked out by the x-linked albinism allele). CC confers black, Cc makes grey (like all of the male parents, and all of the female parents would have been had they not had the albino trait), and cc makes cream and kills (which is why the cream children are dead and one quarter of the male albinos).
so the parents genotypes are
Male: (X^R,Y Cc)
Female: (X^r,X^r Cc)
(though the letters may be different)
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