Question

The ratio of phenotype in F2 generation of a dihybrid cross is-
A. 3:1
B. 1:2:1
C. 2:1
D. 9:3:3:1

Answer 1

Hint: The phenotypes obtained were out of the sixteen possible allele combinations obtained by crossing the male and female gametes where two traits are taken into consideration.

Complete answer:
A cross that includes the examination of two autonomous characteristics is named as dihybrid cross. As the third law of Mendel (law of independent assortment), he saw that the F2 descendants of his dihybrid cross had a 9:3:3:1 proportion and delivered nine plants with round; yellow seeds, three plants with round; green seeds, three plants with wrinkled; yellow seeds and one plant with wrinkled; green seeds. From his examination, Mendel saw that the sets of traits inside the parental generation arranged freely from one another, from one generation to another.

For genes on isolated chromosomes, every allele pair shows autonomous isolation. In the event that the F1generation produces four indistinguishable offspring, the F2 generation, which happens by intersecting the individuals from the F1 generation, shows a phenotypic (appearance) proportion of 9: 3: 3: 1.

For example:
Round yellow x Wrinkled green
RRYY x rryy - There are four potential variations of RrYy parent gametes. A dominant R and a dominant Y allele get half of the gametes; a recessive r and a recessive y allele get the other half of the gametes. Every of RY, Ry, rY, and ry generates 25 per cent for both parents.
F1 = RY $\times$ ry = RrYy (Round yellow)
Selfing of F1= RrYy x RrYy
Gametes= RY, Ry, rY, RY, Ry, rY, ry
From Punnett square= F2 Gives a phenotypic proportion of 9: 3: 3: 1

Dihybrid Cross ; Punnett Square

	RY	Ry	rY	ry
RY	RRYY	RRYy	RrYY	RrYy
Ry	RRYy	RRyy	RrYy	Rryy
rY	RrYY	RrYy	rrYY	rrYy
Ry	RrYy	Rryy	rrYy	rryy

Round/Yellow: 9
Round/green: 3
Wrinkled/Yellow: 3
Wrinkled/green: 1
9:3:3:1 phenotypic ratio

Hence the correct answer is option (D) 9:3:3:1.

Additional Information:
Father of Genetics; Gregor Mendel, through his work on pea plants, discovered the key laws of inheritance. He presumed that genes come two by two and are obtained as specific units, one from each parent.

Mendel's Laws of Heredity are communicated as:
1) The Law of Dominance: A living being with substitute kinds of a quality will communicate the structure that is prevailing (dominant).
2) The Law of Segregation: Each procured trademark is described by a quality pair. Parental characteristics are haphazardly isolated to the sex cells so sex cells contain only a solitary nature of the pair. Offspring as needs be secure one inherited allele from each parent when sex cells participate in fertilization.
3) The Law of Independent Assortment: Genes for different credits are organized autonomously from one another so the inheritance of one quality isn't dependent on the inheritance of another.

Note: It is important to know that among the three laws proposed by Mendel, the law of segregation is globally accepted and true. The law of independent assortment carries true only for traits that are situated on different chromosomes.