Question

In a typical mendelian cross which is a dihybrid cross one parent in homozygous for both dominant traits and another parent is homozygous for both recessive traits . In the f2 generation both the parental combinations and recombinations appear. The phenotypic ratio of parents combination to recombinations is

Answer 1

Answer:

Let us take an example of familiar dihybrid cross of round and yellow seed with wrinkled and green seed where round is dominant over wrinkled and yellow is dominant over green.

Genotypes of parents: YYRR (round and yellow) and yyrr (wrinkled and green)

Gametes formed: YR and yr.

F₁ generation: YyRr (all round and yellow).

Selfing

Gametes formed: YR, Yr, yR, and rr

From the cross (shown in attached file), we get four types of phenotypes:

Round and yellow = 9/16 (parental combination)

Round and green = 3/16 (recombination)

Wrinkled and yellow = 3/16 (recombination)

Wrinkled and green = 1/16 (parental combination)

Hence, there are 10 plants with parental phenotype and 6 plants with new combination.

So, the phenotypic ratio of parents combination to recombination

= 10 : 6 or 5 :3