A plant with round seeds is crossed with another plant with round seeds. Round are dominant over oval seeds. When two heterozygous round-seeded plants are crossed, what is expected of their offspring, assuming random chromosome segregation?A) The oval-shaped plant will appear 50% of the time. B) The round-shaped plant will appear 100% of the time. C) The oval-shaped plant will most likely appear 75% of the time. D) The round-shaped plant will most likely appear 75% of the time.

D

Explanation:

This is a typical monohybrid cross involving a single gene coding for seed shape in a plant. The allele for round seeds (R) is dominant over the allele for oval seeds (r) i.e. the round shape will mask the expression of the oval shape in a heterozygous state (Rr).

Hence, in a cross between two heterozygous parents (Rr), alleles on chromosomes will randomly separate into gametes according to Mendel's law of segregation to produce gametes with R and r allele each. When these alleles from male and female parent combine, four offsprings with RR, Rr, Rr and rr genotypes will be produced.

RR, Rr and Rr genotypes will be phenotypically round-seeded while rr will be phenotypically oval-seeded. Therefore, 3/4 × 100 = 75% of the offsprings will be round-seeded.

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