somebody help me please A cross is performed between a bird that is homo for red feathers and a bird that is homo for blue feathers. Purple offspring result due to incomplete dominance. Then, two of the purple offspring are crossed. What proportion of the offspring from the second cross will be purple? 1 in 4 2 in 4 3 in 4 4 in 4

The proportion of the offspring from the second cross that would be purple will be 2 in 4.

Let us assume that the red feather color is controlled by allele A and that of blue feather color is controlled by allele B.

Homzygous red feather birds will have the genotype AA

Homzygous blue feather birds will have the genotype BB

Crossing the 2 birds:

                             AA     x     BB

                         AB    AB    AB    AB

Thus, the purple offspring are AB.

Crossing 2 of the purple offspring:

                                    AB    x    AB

                              AA    AB    AB    BB

1 AA - red

2 AB - purple

1 BB - blue

Thus, 2/4 or 1/2 or 50%  of the offspring from the second cross will be purple.

More on incomplete dominance can be found here: link

2 in 4

Explanation:

Let PP are the gametes of red feather bird and pp are the gamete of blue feather bird. In the first cross they both will give purple feather bird because of incomplete dominance.

Consider Pp as the allele of purple offspring for the second cross. When two of the purple offspring are crossed, it will give the proportion of 2 in 4  

F2: Pp X Pp

Offspring: PP, Pp,Pp, pp

So, only two offspring, Pp is with purple feathers while PP has red and pp has blue feathers.

Hence, the correct option is 2 in 4.

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