Question

In sickle-cell anemia, the sequence of amino acids from first to the seventh position of beta-chain of hemoglobin S (Hbs) is __________.
A. His, Leu, Thr, Pro, Glu, Val, Val
B. Val, His, Leu, Thr, Pro, Glu, Glu
C. Thr, His, Pro, Val, Pro, Val, Glu
D. Glu, His, Leu, Pro, Val, Glu, Glu
E. Val, His, Leu, Thr, Pro, Val, Glu

Answer 1

Sickle-cell anemia is an autosomal recessive disease. This means that a recessive genotype is present on the autosome codes for it. Autosomes are the somatic or non-sex chromosomes. There are twenty-two pairs of autosomal chromosomes in the human body.

Complete answer:
Sickle cell anemia is transmitted from the parents to offspring when both the male and the female parents are the carrier of the Sickle cell trait. This means that they both should have the heterozygous condition for the gene.
The Sickle cell anemia disease or defect is caused by the mutation or the transversion or substitution mutation of a gene that controls the Beta-chain of the hemoglobin. This gene is present on chromosome 11. This mutated form of the gene is $H{b^S}$. The $H{b^S}$ allele causes one amino acid to change in the Beta-chain sequence. This allele replaces the glutamic acid present at the sixth position of the normal Beta-chain with the amino acid valine. This is because of the GAG codon in normal mRNA codes for glutamic acid. In SCA it mutates to GUG which then codes for valine.
The normal sequence of Beta-chain peptides is Val, His, Leu, Thr, Pro, Glu, Glu.
The mutant sequence of Beta-chain peptides is Val, His, Leu, Thr, Pro, Val, Glu.
The hemoglobin of the mutant person undergoes polymerization under low oxygen tension. This causes the change in the shape of the red blood cells from biconcave discs to elongated sickle-like structures.

Thus, based on the above information we can say that option B) is the correct answer.

Note: The sickle cell anemia disease is controlled by a single pair of alleles, with the forms $H{b^A}$ and $H{b^S}$. These two alleles form three different combinations of genotypes in our population. These three genotypes are as follows –
$H{b^A}H{b^A}$ - Organisms with this genotype are normal.
$H{b^A}H{b^A}$ - Organisms with this genotype are the carriers.
$H{b^A}H{b^A}$ - Organisms with this genotype are affected by the disease. Such individuals die before attaining maturity.