Question

The agouti locus in mice has three alleles a, A and A^Y. Use the following cross results to answer the following questions.

P: aa (black) x AA (agouti) --> F1: all agouti --> F2: 3 agouti : 1 black

P: A^Ya (yellow) x  A^Ya (yellow) --> F1: 2/3 yellow : 1/3 black

P: AA (agouti) x AA^Y(yellow) --> F1: 1/2 agouti : 1/2 yellow

a) The A^Y allele is dominant for yellow coat color.     (Click for List) True False   

b) The A allele can be dominant or recessive for coat color.     (Click for List) True False   

c) The A^Y allele is recessive for survival.     (Click for List) True False   

d) The a allele is recessive for survival.     (Click for List) True False   

e) The alleles at the agouti locus act epistatically to distort the expected 3:1 phenotypic ratio in the F2 progeny.     (Click for List) True False   

In addition, the independently assorting c allele is recessive (to C) and prevents the mice from making any fur pigments at all, resulting in albinos regardless of the genotype at the agouti locus. Two mice with the genotype A^Ya Cc are crossed what are the ratios of progeny phenotypes?

    (Click for List) 9 yellow: 3 black: 3 agouti: 1 albino 2 yellow: 1 black : 1 albino 9 yellow: 3 black : 4 albino 9 yellow: 3 black : 3 albino 1 yellow: 1 black : 2 albino 3 yellow: 1 albino   

A graduate student researching the genetics of mouse coat color identifies another lineage of true-breeding black mouse. When this mouse is crossed to true-breeding agouti mice, all progeny were agouti. The student crossed the new mutant to aa mice and found that all of the F1 progeny were agouti.

What can the graduate student conclude about the genetic basis of this new coat color mutation?  

		The new allele is at the agouti locus.
		The new allele is at a locus that is not agouti.
		The two black alleles act epistatically.
		The two black alleles show incomplete dominance.

If the student crosses two F1 progeny, what is the expected phenotypic ratio among the F2 progeny?

(The questions in bold are the ones I'm having the most trouble with.)

Answer 1

1. The AY allele is dominant for yellow coat colour in mice. This statement is true. Y allele is dominant for yellow mice colour but recessive for lethality. It is also termed as lethal gene which mean a specific gene which regulate the character and also regulate the viability of an organism. When this gene comes in homozygous condition, causes the death of organism.

2.  False.  The A allele is hypostatic gene which is a recessive epistatic. When an epistatic gene itself present in recessive form and suppress the expression of another non allelic gene then this condition is called recessive epistatic. Here the non allelic gene is the hypostatic gene.

3.True.  The AY allele is recessive for survival because it is a lethal gene.

4. False​​​​​​. The a allele is the non allelic gene which is a hypostatic gene. It is not responsible for the survival of organism but it gives the color of the coat to the organism.

5. True.