True-breeding female rats with yellow bodies and rosy eyes were crossed with tru

Question

True-breeding female rats with yellow bodies and rosy eyes were crossed with true-breeding wild-type males with gray-brown bodies and red eyes. The F1 rats were inbred to produce an F2 generation. The phenotypes of the F2 were as follows:

yellow, rosy

Yellow ,red

gray-brown, rosy

gray-brown, red

F2 males

1/8

3/8

1/8

3/8

F2 females

1/8

3/8

1/8

3/8

a) How are these traits inherited?

b) Using symbols of your own choice draw a diagram showing the inheritance of the alleles producing the yellow and rosy traits in this cross.

c) What were the phenotypes of the F1 males and females from this cross?

d) Diagram the F2 results using the branch diagram method.

yellow, rosy

Yellow ,red

gray-brown, rosy

gray-brown, red

F2 males

1/8

3/8

1/8

3/8

F2 females

1/8

3/8

1/8

3/8

Explanation / Answer

a. Autosomal Dominant. That is because In both genders equally distributed so Autosomal. All are expressed in Heterozygous condition. So Dominant. The inheritance pattern is Autosomal Dominant.

y = yellow Body; r = rosy trait. (Mutants)

Y = Gray Brown body; R = Red eye (Wild type)

True breeding: yyrr. As yellow body & rossy traits are mutants, they only express this character in homozygous recessive conditions. That is in yyrr. In f1 the progeny become YyRr x YyRr

So only yyrr gives Yellow body and Rossy trait.

C. F1 gives only single phenotype I.e Gray-Brown body with Red eyes

D. In both male and females, 1:3:1:3 ratios of Yellow-rossy; Yellow-red; Gray-brown rossy and Gray Brown-Red.

YR. (YR, Yr, yR, yr) = YYRR, YYRr, YyRR, YyRr.

Yr. (YR, Yr, yR, yr) = YYRr, YYrr, YyRr, Yyrr   

yR. (YR, Yr, yR, yr) = YyRR, YyRr, yyRR, yyRr

yr (YR, Yr, yR, yr) = YyRr, Yyrr, yyRr, yyrr

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