Question

${ Hb }^{ A }$ and ${ Hb }^{ S }$ alleles of normal and sickle celled RBC are
(A) Dominant-recessive alleles
(B) Polygenic alleles
(C) Codominant alleles
(D) Multiple alleles

Answer 1

Hint: ${ Hb }^{ A }$ and ${ Hb }^{ S }$ alleles of normal and sickle celled RBC show a condition where neither allele can mask the expression of the other, that is, neither allele is completely dominant, hence they are both expressed together.

Complete answer:
The parental alleles, both are expressed within the ${ F }_{ 1 }$ progeny are called codominant alleles and therefore the process is named Codominance. In individuals the parental alleles HbA HbS are present within the type of a pair in the progeny, sickle cell anemia appears within the progeny.
In normal conditions, RBCs are Biconcave disc-like.
Sickle cell anemia is known to be a group of disorders that comes under sickle cell disease.
It is known to be an autosomal recessive disease therefore it can be transmitted from parents of the offspring when both female and male individuals are carriers for the gene. This disease is known to be controlled by a single pair of alleles, HbA and HbS. Thus, three genotypes are possible in this
situation:
- ${ Hb }^{ A } { Hb }^{ A }$ (normal homozygous)
- ${ Hb }^{ A } { Hb }^{ S }$ (normal carrier)
- ${ Hb }^{ A }$ ${ Hb }^{ S } { Hb }^{ S }$ (diseased, die before attaining maturity)
Heterozygous ( ${ Hb }^{ A } { Hb }^{ S }$) individuals appear to be unaffected but they are known to be carriers of this disease because there is a 50 percent probability of the transmission of the mutant gene to the progeny, thus exhibiting sickle cell trait.

So, the correct answer is ‘Codominant alleles’

Note:
-There is no cure for most people with sickle cell anemia but treatments relieve pain and help prevent complications associated with the disease.
-In carriers, the RBCs are usually found to be biconcave in shape in normal conditions, only changing to curved shape when there is low oxygen tension in the body.
-In the carriers, people make both, normal hemoglobin and sickle cell hemoglobin.
-Their blood might contain some of the sickle cells but they generally do not have any symptoms.