Question

In the F${}_2$ generation of a Mendelian dihybrid cross, the number of phenotypes and genotypes are:

• A. phenotypes - 9; genotypes - 4
  
• B. phenotypes - 4; genotypes - 16
  
• C. phenotypes - 4; genotypes - 9
• D. phenotypes - 4; genotypes - 8
  

Answer 1

The correct option is C phenotypes - 4; genotypes - 9

Dihybrid cross :

A cross involving two pairs of contrasting characters is called a dihybrid cross.

Example of a dihybrid cross :

Below given is the dihybrid cross between a plant with round yellow (RRYY) seeds and wrinkled green (rryy) seeds producing pea plants.

Dihybrid Cross :
YR Yr yR yr YR Yr yR yr

YYRR	YYRr	YyRR	YyRr
YYRr	YYrr	YyrR	Yyrr
YyRR	YyRr	yyRR	yyRr
YyRr	Yyrr	yyRr	yyrr

No. of phenotypes in a dihybrid cross

The set of observable characteristics of an individual like height and colour is called phenotype. Phenotypes obtained from the above cross are pea plants producing the following kinds of seeds in the ratio of 9:3:3:1 :-

• Round yellow: Parental variety
• Round green: Recombinant variety
• Wrinkled yellow: Recombinant variety
• Wrinkled green: Parental variety

Hence, the number of phenotypes is 4.
No. of possible phenotypes in a dihybrid cross is 4

No. of genotypes in a dihybrid cross :

Genotype refers to the genetic constitution of an organism. Genotypes obtained from the above cross are YYRR, YYRr, YYyy, YyRR, YyRr, Yyrr, yyRR, yyRr, yyrr in the ratio of 1: 2: 1: 2: 4: 2: 1: 2: 1.
Hence, the number of possible genotypes is 9.

Final answer :
d.) phenotypes - 4; genotypes - 9