Question

In corn, three dominant alleles, called A, C, and R, must be present to produce colored seeds. Plants that are “A-C-R-“ are colored; all others are colorless. A colored plant of unknown genotype is crossed with three tester plants of known genotype. With tester aaccRR, the colored plant produces 50% colored seeds. With aaCCrr, it produces 25% colored. With AAccrr, it produces 50 percent colored. What is the genotype of the colored plant?

Answer 1

A, C, R are dominant alleles that must be present to produce a colour seed.

Plants that are A_C_R are coloured.

The unknown plant is crossed with tester plant to produce specific percentage of coloured seeds.

• With aaccRR - 50% coloured.
• With aaCCrr - 25% coloured.
• With AAccrr - 50% coloured.

From this we can infer :-

?There must be two recessive alleles present in the genoytype.

?When test crossed with aaCCrr it yields the minimum i.e. 25% of coloured seeds which means that the recessive allele are "a" and "r".

The genotype of the coloured plant is AaCCRr.

Lets us perform the crosses to verify the same.

Cross I :-

Parents :- AaCCRr × aaccRR

Gametes :- ACR, ACr, aCR, aCr × acR

Offsprings :-

Punnett square

Gametes↓/→	ACR	ACr	aCR	aCr
acR	AaCcRR	AaCcRr	aaCcRR	aaCcRr

So there is 50% coloured seeded plants in the progeny.

Cross II :-

Parents :- AaCCRr × aaCCrr

Gametes :-  ACR, ACr, aCR, aCr × aCr

Offsprings :-

Punnett square

Gametes↓/→	ACR	ACr	aCR	aCr
aCr	AaCCRr	AaCCrr	aaCCRr	aaCCrr

In this case there is 1/4 or 25% coloured seeded plants in the progeny.

Cross III :-

Parents :- AaCCRr × AAccrr

Gametes :-  ACR, ACr, aCR, aCr × Acr

Offsprings :-

Punnett square

Gametes↓/→	ACR	ACr	aCR	aCr
Acr	AACcRr	AACcrr	AaCcRr	AaCcrr

In this case there is 1/2 or 50% coloured seeded plants in the progeny.

From above, it can be concluded that the Genotype of the coloured plant is AaCCRr .