Question

YyRR is crossed with yyRR. The progeny will be
A. 1 YyRR:1 yyRR
B. 3 YyRR:1 yyRR
C. 1 YyRR:3 yyRR
D. YyRR only

Answer 1

Hint: ‘Y’ is dominant over ‘y’ and ‘R’ is dominant over ‘r’. Working out the cross in a Punnett square will help in solving the cross with ease.

Complete Answer:
Let us work out the cross mentioned in the question using a Punnett square.
PARENT 1- YyRR; gamete 1-YR and gamete 2-yR
PARENT 2- yyRR; gamete 1- yR and gamete 2- yR

PUNNETT SQUARE	PARENT 2
	yR	yR
PARENT 1	YR	YyRR	YyRR
	yR	yyRR	yyRR

From the cross worked out in the above Punnett square, we can see that the gametes from both parents combine to give rise to progeny with two characteristic genotypes, YyRR and yyRR. The chance for occurrence of each of these genotypes is 50%.

Now, let us look at each option one by one.
- 1 YyRR:1 yyRR, since the chance for occurrence of both the genotypes is 50%, the ratio given in this option is correct.
- 3 YyRR:1 yyRR, the chance for occurrence of both the genotypes is 50% and not 75%:25%; therefore, the ratio given in this option is incorrect.
- 1 YyRR:3 yyRR, the chance for occurrence of both the genotypes is 50% and not 25%:75%; therefore, the ratio given in this option is incorrect.
- YyRR only, clearly, there are two different genotypes observed in the progeny. Therefore, this option is incorrect.

Thus, the correct answer for this question is (A) 1 YyRR:1 yyRR.

Note: Crossover between plants having different genotypic and phenotypic traits was first studied by Gregor Mendel, the father of modern genetics. The punnett square was developed by Reginald C Punnett to ease the process of determination of the probability of an offspring to have a particular genotype.