Question

When a pea plant with yellow round seed was crossed with a plant with green wrinkled seeds, yellow round, yellow wrinkled, green round and green wrinkled seed producing varieties were obtained in almost equal numbers. The genotypes of the patents in this cross are:
A. $YYRR \times yyrr$
B. $YyRr \times yyrr$
C. $YYRr \times yyrr$
D. $YyRR \times yyrr$

Answer 1

Hint: Gregor Mendel, the father of genetics performed a series of experiments using a pure breeding garden pea plant (Pisum sativum). Mendel selected the garden pea plant because it possessed a contrasting pair of characters. When he used two contrasting characters for studying inheritance patterns, the experiment came to be known as Mendel’s dihybrid experiment.

Complete answer:
Garden pea plant (Pisum sativum) possesses seven pairs of contrasting characters, used by mendel for studying inheritance patterns. Mendel before commencing his experiments raised pure breeding pea plants which are homozygous for a particular trait. In pea, yellow and round seeds are dominant over green and wrinkled seeds. The parents with genotype, $YyRr \times yyrr$, will produce parental progenies (yellow round and green wrinkled) and non-parental progenies (yellow wrinkled and green round) in almost equal numbers.

On crossing: $YyRr \times yyrr$
Gametes - $YR, Yr, yR, yr$

	yr
YR	YyRr ( Yellow round)
Yr	Yyrr ( Yellow wrinkled)
yR	yyRr ( Green round)
yr	yyrr ( Green wrinkled)

On finding out the genotypic ratio, we can infer that progeny obtained by this cross are in ratio 1 ( Yellow round): 1 ( Yellow wrinkled): 1( Green round) : 1 ( Green wrinkled). The ratio between parental progenies and non-parental progenies is also the same i.e. 2:2 or 1:1.

Hence the correct option is (B).

Note:- The cross mentioned above is also known as test cross. A test cross is used to determine the genotype of progeny obtained during a cross. In a dihybrid experiment, when heterozygous progeny for both the genes (YyRr) is crossed with a homozygous recessive parent (yyrr), it is termed as Test cross.