Question

Assuming that the parents are pureline for the contrasting characters, offsprings with non-parental phenotypes in F2 generation of dihybrid cross show

• A. none of these
• B. dominant trait for one character and recessive for the other
• C. dominant traits for both characters
• D. recessive traits for both characters

Answer 1

The correct option is B dominant trait for one character and recessive for the other

Let’s consider Mendel’s dihybrid cross in which two pea plants pureline for producing round, yellow seeds (RRYY) and wrinkled, green seeds (rryy) are crossed.
F2 generation:-
$\begin{array}{ccccc}\text{Gametes}& \text{RY}& \text{Ry}& \text{rY}& \text{ry}\\ \text{RY}& \text{RRYY}& \text{RRYy}& \text{RrYY}& \text{RrYy}\\ & \text{(Round, yellow)}& \text{(Round, yellow)}& \text{(Round, yellow)}& \text{(Round, yellow)}\\ \text{Ry}& \text{RRYy}& \text{RRyy}& \text{RrYy}& \text{Rryy}\\ & \text{(Round, yellow)}& \text{(Round, green)}& \text{(Round, yellow)}& \text{(Round, green)}\\ \text{rY}& \text{RrYY}& \text{RrYy}& \text{rrYY}& \text{rrYy}\\ & \text{(Round, yellow)}& \text{(Round, yellow)}& \text{(Wrinkled, yellow)}& \text{(Wrinkled, Yellow)}\\ \text{ry}& \text{RrYy}& \text{RrYy}& \text{rrYY}& \text{rrYy}\\ & \text{(Round, yellow)}& \text{(Round, green)}& \text{(Wrinkled, yellow)}& \text{(Wrinkled, green)}\end{array}$
In F2 generation, the progenies producing round, yellow seeds and those producing wrinkled, green seeds display parental phenotypes. Any deviations from these characters are classified under non parental phenotypes. Non- parental phenotypes include progeny plants producing yellow, wrinkled seeds and green, round seeds.
As observed in the cross above, the genotypes of the non-parental phenotypes are mentioned as follows:
$\begin{array}{cc}\text{Non-parental phenotype}& \text{Corresponding genotype of the}\\ & \text{plant exhibiting the phenotype}\\ \text{Yellow, wrinkled seeds}& \text{YYrr}\\ & \text{Yyrr}\\ \text{Green, round seeds}& \text{yyRR}\\ & \text{yyRr}\end{array}$
For both the non-parental characters, the genotype of one of the characters is dominant while that of the other is recessive.
Hence, non parental phenotypes in F2 generation of dihybrid cross show dominant trait for one character and recessive for the other.
This is due to an independent assortment of chromosomes during meiosis.