Question

In rats, gene B produces black coat color if the genotype is B–, but black pigment is not produced if the genotype is bb. At an independent locus, gene D produces yellow pigment if the genotype is D–, but no pigment is produced when the genotype is dd. Production of both pigments results in brown coat color. If neither pigment is produced, coat color is cream. Determine the genotypes of parents of litters with the following phenotype distributions.

Part A 4 brown, 4 black, 4 yellow, 4 cream Enter your answers separated by a comma. For example, for BBDD, BbDd enter BBDD,BbDd. SubmitRequest Answer Part B 3 brown, 3 yellow, 1 black, 1 cream Enter your answers separated by a comma. For example, for BBDD, BbDd enter BBDD,BbDd. SubmitRequest Answer Part C 12 brown, 4 black 12 brown, 4 black At the B locus, both parents were BB. At the D locus, one parent was Dd and the other was dd. At the B locus, both parents were BB. At the D locus, both parents were Dd. At the B locus, one parent was BB and the other parent could have had any genotype (BB, Bb, or bb). At the D locus, one parent was Dd and the other was dd. At the B locus, one parent was BB and the other parent could have had any genotype (BB, Bb, or bb). At the D locus, both parents were Dd. SubmitRequest Answer Return to AssignmentProvide Feedback

Answer 1

Answer: The corresponding genotypes and the phenotypes according to the information provided are as follows

Phenotypes	Genotypes
Brown coat colour	BBDD, BbDd
Black coat colour	BBdd,Bbdd
Yellow coat colour	bbDD,bbDd
Cream coat colour	bbdd

Part A: If the expected phenotypes are 4 brown, 4 black, 4 yellow, 4 cream

The ratio is 1:1:1:1

It is a typical test cross ratio obtained, if one of the parents is heterozygous.

Hence the genotypes of parents would be BbDd and bbdd

gamates	BD	Bd	bD	bd
bd	BbDd brown	Bbdd black	bbDd yellow	bbdd cream

Part B: If the expected phenotypes are 3 brown, 3 yellow, 1 black, 1 cream

Then the parental genotype will be BbDd and bbDd

gamates	BD	Bd	bD	bd
bD	BbDD brown	BbDd brown	bbDD yellow	bbDd yellow
bd	BbDd brown	Bbdd black	bbDd yellow	bbdd cream

Part C: If the expected phenotypes are 12 brown:4 black, the ratio is 3:1

Then at the B locus, both parents were BB. At the D locus, both parents were Dd.

The cross would be BBDd and BBDd

gamates	BD	Bd
BD	BBDD brown	BBDd brown
Bd	BBDd brown	BBdd black

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