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1. Alpha thalassaemia is a blood condition resulting from abnormalhaemoglobin production, due to loss of function of copies of eitherHBA1 or HBA2 genes. These genes are very similar and next to eachother on the chromosome; for simplicity’s sake we talk about havingfour copies of the HBA gene (two alleles, with two HBA copies oneach allele).

Alleles are depicted with α representing a functioning HBA gene,and - representing a non-functioning gene. For example, thegenotype α-/αα represents someone with one allele with only one HBAcopy functioning, and a second allele with both HBA copiesfunctioning.

There are multiple phenotypes of alpha thalassaemia, whichgenerally depend on how many of the four HBA copies arefunctioning. This is outlined in the table below:

Phenotype	Genotype	Symptoms / severity
α-thalassaemia major	Loss of 4 HBA genes	Severe onset from birth - death usually occurs in newbornperiod
Haemoglobin H (HbH) disease	Loss of 3 HBA genes	Generally severe - anaemia, possible bone issues, may requireblood transfusions
α-thalassaemia trait	Loss of 2 HBA genes	Generally mild - usually only detectable via blood cellinvestigation
α-thalassaemia silent carrier	Loss of 1 HBA gene	No or few symptoms - often not detectable even via blood cellinvestigation

Both Indian and Southeast Asian populations have relatively highrates of alpha thalassaemia.

In Indian populations, alleles with one HBAgene copy deleted are the common cause of alpha thalassaemiaconditions. Alleles with both HBA gene copies deleted are rare.

In Southeast Asian populations, alleles withboth HBA gene copies deleted are the common cause of alphathalassaemia conditions. Alleles with one HBA gene copy deleted arerare.

You are providing genetic counselling to an Indian couple, bothof whom have alpha thalassaemia trait due to mutations commonlyseen in their population.

Regarding alpha thalassaemia, what are the phenotypespossible for a pregnancy for this couple? Give the chance of eachphenotype.