Answer:
There is a 25% chance that the offspring will have sickle cell anemia (SS)
Explanation:
Sickle cell anemia is a genetic disease, where red blood cells can take the shape of a crescent (sickle), and this change allows the red blood cells to be more easily destroyed, causing anemia. Sickle cell anemia is caused by defective hemoglobin (Hb), which is the oxygen carrying protein in blood cells. Hemoglobin is made up of four peptide chains, each bound to a heme group. Different hemoglobins have different combinations of these chains. Hemoglobin A (HbA) is the primary hemoglobin affected in sickle cell, because their beta-globin chains end up misshapen because of a genetic mutation in the beta-globin gene. Sickle cell anemia is an autosomal recessive disease, so there needs to be a mutation in both copies of the beta-globin gene in order to get the disease. If a person has just one copy of the mutated gene and the other copy is normal for the gene, then they are a sickle cell carrier.
So first of all, this looks like a dihybrid cross, but it is not because we are dealing with one pair of alleles (gene that causes sickle cell), so we will actually be doing a monohybrid cross.
So let’s go through the alleles step by step:
Hb = hemoglobin (constant, all red blood cells have hemoglobin, we are looking at the mutation in the beta globin gene of the hemoglobin which will be the allele we focus on)
SS = sickle cell (mutated beta globin gene (S) x 2)
AA = normal beta globin gene (A) x 2 (no sickle cell)
AS = carrier (one sickle cell gene + one normal gene)
HbAS x HbAS
Carrier x carrier
PARENTS A S
A AA AS
S AS SS
25% chance that the offspring will have a normal (does not have sickle cell anemia) genotype (AA)
50 % chance that the offspring will be carriers (AS)
25% chance that the offspring will have sickle cell anemia (SS)
