In a genetic cross diagram, which plants must all be heterozygous?

• A. Plants with genotype Aa
• B. Plants with genotype AA
• C. Plants with genotype aa
• D. Plants with genotype AABB

Answer: (A)

Verified step by step guidance

1. Understand the concept of heterozygosity: In genetics, a heterozygous organism has two different alleles for a particular gene. For example, the genotype 'Aa' indicates heterozygosity, where 'A' and 'a' are different alleles.
2. Identify the genotypes given in the problem: The genotypes provided are Aa, AA, aa, and AABB.
3. Analyze each genotype: The genotype 'Aa' consists of two different alleles, making it heterozygous. The genotype 'AA' consists of two identical alleles, making it homozygous dominant. The genotype 'aa' consists of two identical alleles, making it homozygous recessive. The genotype 'AABB' consists of two pairs of identical alleles, making it homozygous for both genes.
4. Determine which genotype is heterozygous: Based on the analysis, the genotype 'Aa' is the only one that is heterozygous because it contains two different alleles.
5. Conclude which plants must be heterozygous: Plants with the genotype 'Aa' must all be heterozygous, as they have one dominant allele 'A' and one recessive allele 'a'.