Understanding Monohybrid Cross and Offspring Genotypes

What are the genotypes of the parents in the monohybrid cross?

If the following offspring genotypes are predicted (25% BB, 25% bb, and 50% Bb).

Final answer:

The genotypes of the parents in a monohybrid cross, where offspring are distributed as 25% BB, 25% bb, and 50% Bb, would both be heterozygous (Bb). A Punnett square predicts these offspring genotypes from a cross of two heterozygous individuals (Bb x Bb), showing classic Mendelian inheritance patterns.

Explanation:

The genotypes of the parents in a monohybrid cross leading to a predicted distribution of offspring can be deduced from the provided genotypic ratios. If offspring genotypes are in a ratio that shows 25% BB, 25% bb, and 50% Bb, the parents are both heterozygous (Bb). This is because a Punnett square for a cross between two heterozygous individuals yields exactly these proportions: one BB, two Bb, and one bb, which is what we see in Mendelian inheritance patterns. For example, considering a case with pea plants, if yellow is dominant (Y) and green is recessive (y), a cross between two heterozygous parents (Yy) will yield offspring that have a 1:2:1 genotypic ratio (YY:Yy:yy) and a 3:1 phenotypic ratio (yellow:green).

In a different scenario, performing a test cross with a heterozygous parent (such as Yy) crossed with a homozygous recessive (yy) plant, would give a 1:1 phenotypic ratio. This indicates that the heterozygous parent can pass on either the dominant or the recessive allele with equal probability.