Explain a genetic cross between two individuals with genotype AS, including gametes, offspring genotypes, genotypic ratio, and phenotypic ratio assuming A is normal and S is sickle cell.

The diagram shows that both parents contribute gametes with alleles A and S. Therefore, both parents have the genotype AS.

The lines connect the gametes from each parent to form the offspring genotypes:

• A (from parent 1) combines with A (from parent 2) to form AA.
• A (from parent 1) combines with S (from parent 2) to form AS.
• S (from parent 1) combines with A (from parent 2) to form AS.
• S (from parent 1) combines with S (from parent 2) to form SS.

The resulting genotypes are AA, AS, AS, and SS.
The ratio of these genotypes is:

In the context of sickle cell disease:

• AA individuals have normal hemoglobin.
• AS individuals have sickle cell trait (they are carriers and usually do not show severe symptoms).
• SS individuals have sickle cell anemia.

Therefore, the phenotypic ratio is:

The diagram shows a cross between two heterozygous individuals (AS $\times$ AS), resulting in offspring with genotypes AA, AS, and SS in a $1:2:1$ ratio.

The final answer is $\text{Genotypic ratio: 1 AA : 2 AS : 1 SS}$.