Question

1. sickle cell anemia is a genetic disease which causes malformation of the red blood cells (some of them collapse into a sickle shape.) it is caused by one gene only. individuals who are homozygous for sickle cell anemia tend to die as small children, but hybrids (\carriers\) suffer much less and often live long enough to reproduce.*

a. if a male carrier is crossed with a female carrier, what is the probability of having a child with the actual disease?
b. is sickle cell anemia a sex linked trait? how can you tell?
c. is the gene for sickle cell anemia dominant or recessive? explain.

Explanation:

Step1: Define genotypes of carriers

Carriers are heterozygous: let dominant allele = $A$, recessive = $a$. Carriers: $Aa$.

Step2: Set up Punnett square

Male gametes: $A$, $a$; Female gametes: $A$, $a$. Punnett square:

	$A$	$a$
$a$	$Aa$	$aa$

Step3: Calculate disease probability

Disease requires homozygous recessive ($aa$). 1 out of 4 genotypes: $\frac{1}{4}$.

Step4: Analyze sex-linked trait

Sex-linked traits are on X/Y chromosomes. The problem states it’s caused by one gene with carriers (heterozygotes) in both sexes, no sex bias mentioned—so not sex-linked.

Step5: Determine dominance

Carriers ($Aa$) don’t have the disease; only homozygous recessive ($aa$) do. So the disease allele is recessive.

Answer:

a. $\frac{1}{4}$
b. No; it is caused by a single gene with carriers in both sexes (no sex chromosome link).
c. Recessive; carriers (heterozygotes) do not have the disease, only homozygous recessive individuals do.