Question

When a cross is made between a tall plant with yellow seeds (Tt Yy) and a dwarf plant with green seeds (Tt yy), what is true regarding the proportions of phenotypes of the offsprings in the F1 generation?

	Proportion of tall and green	Proportion of dwarf and Green
A.	$\dfrac{3}{8}$	$\dfrac{1}{8}$
B.	$\dfrac{2}{8}$	$\dfrac{1}{8}$
C.	$\dfrac{1}{8}$	$\dfrac{3}{8}$
D.	$\dfrac{2}{8}$	$\dfrac{2}{8}$

Answer 1

Hint: Mendel performed dihybrid cross on a pea plant taking two traits like height and colour, shape of the seed etc. A hybrid organism is a heterozygous that carries two different alleles of the same gene at the same loci. He put forward the law of independent assortment as a result of dihybrid cross.

Complete Answer:
According to the question, the cross was made between a tall plant with yellow seeds (Tt Yy) and a dwarf plant with green seeds (Tt yy).
The tall plant (T) is dominant over dwarf (t) and yellow seed (Y) is dominant over green(y).
When the cross is done between (Tt Yy) X (Tt yy), the F1 generation will be as follows

	TY	Ty	tY	ty
TY	TTYY(Tall, Yellow)	TTYy(Tall, Yellow)	TtYY(Tall, Yellow)	TtYy(Tall, Yellow)
Ty	TTYy(Tall, Yellow)	TTyy(Tall,green)	TtYy(Tall, Yellow)	Ttyy(Tall,green)
tY	TtYy(Tall, Yellow)	TtYy(Tall, Yellow)	ttYY(Dwarf, Yellow)	ttYy(Dwarf, Yellow)
ty	TtYy(Tall, Yellow)	Ttyy(Tall,green)	ttYy(Dwarf, Yellow)	ttyy(Dwarf, green)

The phenotypes obtained is as follows-
Tall and yellow- 9, Tall and green-3, dwarf and yellow-3, dwarf and green -1
According to the question- proportion of tall and green and proportion of dwarf and Green is 3 and 1 respectively.

Thus the correct answer is A.

Note: The principle of Independent assortment states that the allele of one gene separates from one another gene independently during the formation of reproductive cells. It is useful because it produces a new genetic combination which leads to variation in the population. The phenotype ratio of the F1 generation of dihybrid cross is 9:3:3:1.