Question

What percent of the offspring will receive the recessive phenotype when crossing two heterozygous individuals? assume normal dominance?

Answer 1

Answer:

25%

Explanation:

According to normal i.e. Mendelian dominance if 2 heterozygotes for a particular character are crossed then phenotypically, 25% off-springs will show recessive trait while 75% will show dominant trait.

Let us consider a pea plant for seed shape character in which 'R' allele represents dominant character and gives round shape while 'r allele' is responsible for recessive character and gives wrinkled shape to seeds.

The cross is depicted as under:

Parentals              Rr           x         Rr

                          /        \                  /     \

Progeny          RR       Rr          Rr         rr          

Hence, 3 (RR, Rr & Rr) out of the 4 off-springs will show dominant trait while only 1 (rr) will have recessive trait. The progeny with 'Rr genotype' will also show dominant trait phenotypically because R allele which is dominant will mask the expression of r allele which is responsible for recessive phenotype.

Answer 2

The answer is 25%. The other 75% will have dominant phenotype. However, in the dominant phenotype, 25% have a homozygous dominant genotype, while the remaining 50% have a heterozygous genotype. Find attached a punnet square that will clearly illustrate this;