Question

this passage describes the sickle-cell disease trait in humans: sickle-cell disease is a condition that affects red blood cells. red blood cells are disc - shaped cells in the blood that carry oxygen throughout the body. humans with sickle - cell disease have red blood cells shaped like crescents. these cells may get stuck in blood vessels, preventing oxygen from reaching the rest of the body. this lack of oxygen can cause pain and fatigue. in a group of humans, some individuals have sickle - cell disease and others do not. in this group, the gene for the sickle - cell disease trait has two alleles. the allele for having sickle - cell disease (a) is recessive to the allele for not having sickle - cell disease (a). this punnett square shows a cross between two humans. punnett square with rows and columns labeled a and a (row), a and a (column), cells: aa, aa, aa, aa what is the expected ratio of offspring that do not have sickle - cell disease to offspring that have sickle - cell disease? choose the most likely ratio. 0:4, 3:1, 2:2, 1:3, 4:0

Explanation:

Step1: Analyze Genotypes

From the Punnett square, the genotypes of offspring are \( AA, Aa, AA, Aa \). So all 4 offspring have genotypes \( AA \) or \( Aa \).

Step2: Determine Phenotypes

The allele \( a \) (sickle - cell) is recessive. So only \( aa \) shows sickle - cell disease. Since none of the offspring have \( aa \) genotype, number of non - sickle - cell offspring = 4, number of sickle - cell offspring = 0.

Step3: Find the Ratio

The ratio of non - sickle - cell to sickle - cell offspring is \( 4:0 \).

Answer:

\( 4:0 \)