Question

The genes R, E and D are independently assorting and control production of red pigment as follows (recessive alleles are not functional) precursor -- (R) --> white -- (E) --> yellow -- (D) --> red RREEDD and rreedd individuals are crossed, and their offspring are testcrossed. What proportion of the F₂ progeny is expected to be red?

Answer 1

The proportion of
`F_2` progeny expected to be red is 3/4.

Step-by-step explanation:

Since the genes assort independently, each pigment is inherited independently of one another and expected to follow Mendelian ratio of 3 to 4 at the
`F_2` generation. In heterozygote state, one of the two alleles representing each colour pigment will be dominant while the other one will be recessive.

Taking the alleles for red pigment and following the Mendelian principle;

DD x dd

The
`F_1` progeny will all have the red pigment with genotype Dd according to the Punnet's square (see attached image).

Testcrossing the offsprings

Dd x Dd

From the Punnet's square (see the attached image), 3 out of the 4
`F_2` progeny will have the red pigment while 1 out of 4 will not have.

Hence, the proportion of
`F_2` progeny expected to be red is 3/4