Question

Alpha thalassemia is a blood condition resulting from abnormal hemoglobin production, due to loss of function of copies of either HBA1 or HBA2 genes. These genes are very similar, and for simplicity’s sake we talk about having four copies of the HBA gene (two copies of each).

HBA1 and HBA2 genes are located next to each other, and therefore are described within the same allele. For example, αα indicates that both HBA1 and HBA2 copies on an allele are functioning, α- indicates an allele with one of the two genes functioning, and -- indicates an allele with neither gene functioning. There are multiple versions of alpha thalassemia, which depend on how many of the four HBA copies are functioning.

This is outlined in the table below, in order of severity (most severe -> least severe): Phenotype Genotype α-thalassemia major Loss of all 4 α-globin genes Hemoglobin H (HbH) disease Loss of 3 α-globin genes α-thalassemia trait Loss of 2 α-globin genes in cis (--/αα) or trans (-α/-α) α-thalassemia silent carrier Loss of 1 α-globin gene (-α/αα) A man who is a silent carrier has a child with a woman who has α-thalassemia trait.

a) Assuming the woman has mutations in cis, what are the possible offspring phenotypes for this child? Give the probability for each possible phenotype.

b) Assuming the woman has mutations in trans, what are the possible offspring phenotypes for this child? Give the probability for each possible phenotype.

Answer 1

In Alpha thalassemia genes are transformed by Autosomal recessive gene. it needed genes fom both the parent to get dissease.

If a person have 1 defective alpha gene that condition is called silent carrier. they don't show any symptom but can pass gene to children.

Cis deletion is a condition in which mutated genes are on same chromosome.

Trans deletation in which mutated genes are on two different chromosomes.

Ans a- Cross between carrier male and cis α-thalassemia

Male Carrier Female cis a-thalassemia Parent's Phenotype -aa Genotype Gametes -alaa -a, aa αα F1 generation Genotype Phenotype -al-- Hemoglobin H (HĐH) -alaa carrier --/aa cis a-thalassemia αααα Normal

50% affected 25% carrier 25% normal

Ans b Cross between carrier male and trans α-thalassemia

Male Carrier Female Trans a-thalassemia Parent's Phenotype Genotype Gametes -alaa -a, a a -al-a -a, -a F1 generation Genotype Phenotype -al- a Trans a- thalassemia -al- a Trans a- thalassemia - αι αα carrier - αι αα Carrier

50% affected 50% carrier