Question

which of the following is an accurate genotypic ratio of a cross between 2 heterozygous individuals of any trait?
○ 1:1
○ 1:0
○ 3:1
○ 1:2:1

Explanation:

Step1: Recall Mendelian Genetics

When two heterozygous individuals (let's say genotype \( Aa \)) are crossed, we use a Punnett square. The parents' gametes are \( A \) and \( a \) for each.

Step2: Construct Punnett Square

The Punnett square for \( Aa \times Aa \) is:

	\( A \)	\( a \)
\( a \)	\( Aa \)	\( aa \)

Step3: Determine Genotypic Ratios

Count the genotypes: \( AA \) (1), \( Aa \) (2), \( aa \) (1). So the genotypic ratio is \( 1:2:1 \). The \( 3:1 \) ratio is the phenotypic ratio for a dominant - recessive trait in this cross. \( 1:1 \) is a phenotypic or genotypic ratio for a test cross (e.g., \( Aa\times aa \)), and \( 1:0 \) is not a ratio for a cross of two heterozygotes.

Answer:

1:2:1 (the option with 1:2:1)