The following genotypes of two independently assorting autosomal genes determine coat color in rats: A—B—(gray); A—bb (yellow); aaB—(black); aabb (cream)

A third gene pair on a separate autosome determines whether or not any color will be produced. The CC and Cc genotypes allow color according to the expression of the A and B alleles. However, the cc genotype results in albino rats regardless of the A and B alleles present. Determine the F1 phenotypic ratio of the following crosses:

a. AAbbCC x aaBBcc
b. AaBBcc x AABbcc
c. AaBbCc x AaBbcc.

a) 100% Gray

b) 100% albino

c) 16/32 albino, 9/32 gray, 3/32 yellow, 3/32 black, 1/32 cream

Explanation:

Available data:

Cross a

Parentals)      AAbbCC            x          aaBBcc

Phenotype)     Yellow                           Albino

Gametes) AbC, AbC, AbC, AbC     aBc, aBc, aBc, aBc

                AbC, AbC, AbC, AbC     aBc, aBc, aBc, aBc

F1) 100% AaBbCc, Gray individuals

Cross b

Parentals)       AaBBcc       x           AABbcc

Phenotype)     Albino                         Albino

Gametes) ABc, ABc, ABc, ABc,     ABc, ABc, Abc, Abc,

                 aBc, aBc, aBc, aBc       ABc, ABc, Abc, Abc,

F1) 100% A-B-cc, Albino individuals

Cross c

Parentals)       AaBbCc       x            AaBbcc

Phenotype)        Gray                        Albino

Gametes) ABC, ABc, AbC, Abc,     ABc, ABc, Abc, Abc,

                 aBC, aBc, abc, abc       aBc, aBc, abc, abc

Punnett square)

            ABC         ABc        AbC         Abc        aBC        aBc       abC       abc  

ABc  AABBCc AABBcc AABbCc  AABbcc AaBBCc AaBBcc AaBbCc AaBbcc

ABc  AABBCc AABBcc AABbCc  AABbcc AaBBCc AaBBcc AaBbCc AaBbcc

Abc AABbCc  AABbcc  AAbbCc  AAbbcc  AaBbCc AaBbcc AabbCc Aabbcc

Abc AABbCc  AABbcc  AAbbCc  AAbbcc  AaBbCc AaBbcc AabbCc Aabbcc

aBc AaBBCc AaBBcc  AaBbCc   AaBbcc  aaBBCc  aaBBcc  aaBbCc  aaBbcc

aBc AaBBCc  AaBBcc  AaBbCc  AaBbcc  aaBBCc  aaBBcc  aaBbCc  aaBbcc

abc  AaBbCc  AaBbcc  AabbCc  Aabbcc  aaBbCc   aaBbcc  aabbCc  aabbcc

abc  AaBbCc  AaBbcc  AabbCc  Aabbcc  aaBbCc   aaBbcc  aabbCc  aabbcc

F1)   18/64 = 9/32 A-B-C, Gray

       6/64 = 3/ 32 A-bbC-, Yellow

       6/64 = 3/ 32 aaB-C-, Black

       2/64 = 1/32 aabbC-, Cream

       32/64 = 16/32 A-B-cc + aaB-cc, + A-bbcc + aabbcc, Albino

Ratio: 16:9:3:3:1    

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