Question

sickle cell anaemia shows what like co-dominance

Answer 1

To understand this concept, you need to be familiar with terms homozygous, heterozygous, dominance and codominance. Here are some wikipedia links to get the idea what that means: Zygosity, Dominance (genetics).

Sickle cell anemia is a fully manifesting condition ant it is NOT a codominant condition. The corresponding codominant condition is called sickle cell trait. So what is the difference?

Humans have a gene for one of hemoglobin components (beta-globin). As humans usually have two sequences (alleles) for each gene located in two chromosomes, an individual may have one of the following genotypes for this component: HbA-HbA, HbA-HbS, and HbS-HbS.

If a person has homozygous HbA-HbA genotype, only normal beta-globin is produced and there will be no signs of sickle-cell conditions.

If a person has homozygous HbS-HbS genotype, that person develops full-scale sickle-cell anemia, which is the fully manifesting condition. It is not an example of codominance itself.

Now if a person has heterozygous genotype HbA-HbS, that is when the concepts of incomplete dominance and co-dominance may apply. In such heterozygous organism, both normal and sickle-cell beta-globin are produced. This leads to a subclinical (i. e. not fully manifesting) condition called sickle cell trait.

The co-dominance phenomenon in this case applies because both normal and abnormal hemoglobin are present in the body, i. e. both HbA and HbS alleles exhibit themselves, and neither one of them fully dominates above another (on a molecular level).

It is believed that it was actually this subclinical trait that saved the sickle-cell allele in human population, because people with sickle cell trait are less susceptible to malaria, so more people with this trait survived in areas where malaria is prevalent. If the sickle-cell allele was actually dominant and heterozygous people had fully manifesting, severe anemia, this allele would probably disappear quite soon after it appeared.








Sickle cell anemia can be recessive and codominant.

Alleles:

A-normal

S-sickle cell

or

S-normal

s-sickle cell

It is recessive when there are two copies of sickle cell allele-homozygous (SS or ss).In this case it is manifested as anemia-all of the red blood cells are sickle cells.It is codominant when there is one copy of sickle cell allele-heterozygous (AS or Ss).In this case it isn’t manifested as anemia but there can be some mild symptoms of anemia-half of the blood cells are sickle cells but the other half are normal cells that can afford enough oxygen,so there will be no anemia.

Answer 2

Sickle cell anemia is a fully manifesting condition ant it is NOT a codominant condition. The corresponding codominant condition is called sickle cell trait.