Question

in the f₂ generation of mendels crosses,
all plants had the dominant trait.
half of the plants had the dominant allele.
all plants had both the dominant and recessive alleles.
one in four plants had two alleles for the recessive trait.

Explanation:

Mendel's experiments showed that in the F₂ generation, when two heterozygous (e.g., \(Aa\times Aa\)) are crossed, the genotypic ratio is \(AA:Aa:aa = 1:2:1\). The homozygous recessive (\(aa\)) has two alleles for the recessive trait. The proportion of \(aa\) is \(\frac{1}{4}\).

• Option 1: In \(Aa\times Aa\) cross, \(aa\) shows recessive trait, so not all plants have dominant trait.
• Option 2: The proportion of having dominant allele (\(AA\) and \(Aa\)) is \(\frac{3}{4}\), not half.
• Option 3: \(AA\) has only dominant alleles (\(A\)), \(aa\) has only recessive alleles (\(a\)).
• Option 4: As per the genotypic ratio \(AA:Aa:aa=1:2:1\), the proportion of \(aa\) (two recessive alleles) is \(\frac{1}{4}\).

Answer:

one in four plants had two alleles for the recessive trait.