Question

In the Mendelian dihybrid cross, out of 240 individuals obtained in the F2 generation, how many of the offsprings would be pure homozygous?

• A. 30
• B. 15
• C. 8
• D. 45

Answer 1

The correct option is A

30

The correct option is A

Explanation of the correct option:

1. A simple cross between two pure species using two gene pairs is known as a dihybrid cross.
2. The gametes produced by a cross between a homozygous dominant round yellow plant (RRYY) and a homozygous recessive wrinkled green plant (RRYY) will be RY and RY.
3. Round and yellow phenotypes will be shared by all plants, but genotypically, they will all be heterozygous for both traits (RrYy).
4. Therefore, if we cross two F1 plants, the potential gametes will be quite genotypically RY, Ry, Ry.
5. Round yellow to wrinkled yellow to round green to wrinkled green will be distributed in a 9:3:3:1 ratio in the F2 generation, correspondingly. Dihybrid crossings are utilized to simultaneously predict two qualities.
6. Observing this, we arrive at the ratio shown below:

1:2:1:2:4:2:1:2:1 (1 RRYY : 2 RRYy : 1 RRyy : 2RrYY : 4 RrYy : 2Rryy : 1rrYY : 2 rrYy : 1 rryy respectively)

Hence 2 out of 16 have the pure homozygous condition.

Therefore 1/8th of 240= 30.

Final answer: Pure homozygous offspring will be 30.