Question

In the following tetrahybrid cross AaBbCcDd x AaBbCcDd what proportion of the F2 offspring would be expected to be genotypically AABBCCdd?
A. 3/4
B. 1/2
C. 1/256
D. 81/256
E. 9/256

Answer 1

Answer:

C. 1/256

Explanation:

In the tetrahybrid cross, we have different four groups. Let name them Part (A, B, C &  D).

Let Part A be Aa and Aa... If both traits crosses; we have

         A          a

A       AA        Aa

a        Aa        aa

Hence, there is a total of 4 combinations

Let Part B be Bb and Bb... If both traits crosses; we have

         B          b

B       BB        Bb

b       Bb         bb

Hence, there is a total of 4 combinations

Let C be Cc and Cc ... If both traits crossses; we have

         C           c

C       CC        Cc

c        Cc        cc

Hence, there is a total of 4 combinations

Let D be Dd and Dd... If both traits crosses; we have

         D          d

D       DD       Dd

d        Dd       dd

Hence, there is a total of 4 combinations

A genotype has the 4 groups together. Therefore the possible number of ways of forming the genotype = 4 x 4 x 4 x 4= 256

Now, Probability that the F2 offspring would be expected to be genotypically AABBCCdd = $\frac{number of genotype AABBCCdd}{Total number of genotype in the offsprings}$

= $\frac{1}{256}$