Question

in people sickle cell disease is expressed codominantly. when an individual is heterozygous they have both normal and sickled cells, but has only sickled cells when they have only recessive alleles. what is the phenotypic ratio of offspring with two heterozygous parents? 3 all round cells : 0 mixed round and sickled cells : 1 all sickled cells 1 all round cells : 2 mixed round and sickled cells : 1 all sickled cells 1 all round cells : 0 mixed round and sickled cells : 1 all sickled cells 1 all round cells : 1 mixed round and sickled cells : 0 all sickled cells

Explanation:

Step1: Define Alleles

Let the dominant allele (normal cells) be \( A \) and recessive allele (sickled cells) be \( a \). Heterozygous parents have genotype \( Aa \).

Step2: Punnett Square Setup

Parents: \( Aa \times Aa \). The possible gametes from each parent are \( A \) and \( a \).

	A	a
a	Aa	aa

Step3: Determine Phenotypes

• \( AA \): All round cells (homozygous dominant).
• \( Aa \): Mixed round and sickled cells (heterozygous, codominant).
• \( aa \): All sickled cells (homozygous recessive).

Step4: Count Phenotypes

• \( AA \): 1
• \( Aa \): 2
• \( aa \): 1

Step5: Phenotypic Ratio

Ratio of all round : mixed : all sickled is \( 1:2:1 \).

Answer:

1 all round cells : 2 mixed round and sickled cells : 1 all sickled cells