Question

If two pea plants having red (dominant) colored flowers with unknown genotypes are crossed, 75% of the flowers are red and 25% are white.
The genotypic constitution of the parents having red-colored flowers will be
A. Both homozygous
B. One homozygous and other heterozygous
C. Both heterozygous
D. Both hemizygous

Answer 1

Hint: The dominant allele expresses itself in a heterozygous condition, and the recessive trait can only be expressed in the offspring in homozygous condition.

Complete answer: Since, both the parents have red-colored flowers, this symbolizes that both parents must have at least one dominant allele of the gene responsible for flower color. Again, it is mentioned that 25% of the offsprings have white-colored flowers.
This means that this section of plants has both the recessive allele in their genotype, one inherited from each parent, as the white-colored flower is only possible if the genotype is homozygous recessive.
Therefore, both parents must possess a heterozygous genotype.
This can further be proved by working out the cross:
Let the dominant allele be represented by ‘R’ and the recessive allele by ‘r’.

		Parent 1
		R	r
Parent 2	R	RR	Rr
	r	Rr	rr

Additional information: Gregor Mendel conducted hybridization experiments on approximately 29,000 pea plants. Peas were an ideal choice for Mendel to choose because they had easily observable traits there were 7 of which he could manipulate. He took years of breeding constant family lines to accurate the original constant traits.
So, the correct answer is option C. Both heterozygous.

Note: This is one of the famous crosses, conducted by Mendel, who proposed the laws of inheritance based upon his results. He included ratios and statistics in his studies to increase the credibility of all the data collected from his experiments.