Question

1. sickle-cell anemia is an autosomal recessive genetic disorder that causes red blood cells to change shape. this can cause the red blood cells to become stuck in blood vessels. this blocking can deprive tissues of oxygen and cause organ damage like strokes. one benefit of this is that people who have one or two alleles of the sickle cell disease are resistant to malaria since the red blood cells are not conducive to the parasites. sickle-cell anemia also exhibits incomplete dominance at which the individual who does not have the disease retains immunity to malaria. fill in the punnett square and determine the expected genotypic ratios from crossing homozygous recessive and homozygous dominant parents.

genotypes:
genotypic ratio:
circle all phenotype(s): normal, carrier, has sickle-cell anemia
% of kids with disorder:
% carriers of the disorder:

Explanation:

To solve this, we assume the parents are homozygous recessive (ss) and homozygous dominant (SS) for the sickle - cell trait.

Step 1: Determine the alleles of the parents

The homozygous dominant parent (let's say parent 1) has alleles \(S\) and \(S\), and the homozygous recessive parent (parent 2) has alleles \(s\) and \(s\).

Step 2: Fill in the Punnett square

	\(S\)	\(S\)
\(s\)	\(Ss\)	\(Ss\)

Step 3: Determine the genotypes and their ratios

• Genotypes: All the offspring have the genotype \(Ss\) (heterozygous, carriers).
• Genotypic Ratio: Since all 4 offspring are \(Ss\), the genotypic ratio is \(Ss:Ss:Ss:Ss = 4:0:0\) (or simply all \(Ss\)). In terms of the different genotypes (homozygous dominant \(SS\), heterozygous \(Ss\), homozygous recessive \(ss\)), the ratio of \(SS:Ss:ss=0:4:0\).
• Phenotypes:
• The phenotype "normal" (homozygous dominant \(SS\)): 0 offspring, so 0% of kids have the normal (non - carrier, non - diseased in terms of sickle - cell anemia) phenotype in the traditional dominant - recessive sense, but in the case of incomplete dominance, the \(Ss\) individuals have a phenotype that is a carrier and has some resistance to malaria. The phenotype "has sickle - cell anemia" (homozygous recessive \(ss\)): 0 offspring, so 0% of kids have sickle - cell anemia. The phenotype "carrier" (heterozygous \(Ss\)): 4 out of 4 offspring, so 100% of kids are carriers.
• % of kids with disorder (sickle - cell anemia): Since the disorder is autosomal recessive and the offspring are all \(Ss\) (carriers, not having the full - blown disease), 0% of kids have the sickle - cell anemia disorder.
• % carriers of the disorder: Since all 4 offspring are \(Ss\) (carriers), the percentage of carriers is \(\frac{4}{4}\times100 = 100\%\).

Answer:

• Genotypes: \(Ss\) (all offspring)
• Genotypic Ratio: \(SS:Ss:ss = 0:4:0\)
• % of kids with disorder: \(0\%\)
• % carriers of the disorder: \(100\%\)
• Phenotypes: 100% carriers ( \(Ss\) ), 0% with sickle - cell anemia ( \(ss\) ), 0% with normal (non - carrier, \(SS\)) in the traditional dominant phenotype sense (but in incomplete dominance context, \(Ss\) is a carrier phenotype)