Question

• Using the terms "none," "low," "high," fill out Columns 2 and 3 of the Table III below and write notes in the last column

Table III

Possible genotypes	Risk of sickle cell anemia	Likelihood of surviving malaria	Notes on risks of sickle cell anemia and malaria
SS Homozygous dominant for the wild type beta-globin allele
Ss Heterozygous for the wild type beta-globin allele "Sickle cell trait"= carrier
ss Homozygous recessive for the wild type beta-globin allele	will develop sickle cell anemia

Post-Lab questions               

The term "heterozygote advantage" refers to the situation when carrying two copies of an allele is disadvantageous, but carrying only one copy is advantageous.

1. Is the term "heterozygote advantage" relevant when describing the sickle cell allele frequency maintained by malaria? Explain.
2. Explain why natural selection did not remove the sickle cell allele from the population?

Answer 1

Sickle cell anemia trait is an autosomal recessive.

homozygous dominant - normal

heterozygous - carrier

homozygous recessive - affected

Faulty gene of sickle cell anemia doesn't protect against malarial infection but prevents the disease from taking hold after being infected.

Possible genotypes	Risk of sickle cell anemia	Likelihood of surviving malaria	Notes on risks of sickle cell anemia and malaria
SS Homozygous dominant for the wild type beta-globin allele	NONE	LOW (approximately 6%)	the mortality rate for normal patients is higher than that of patients suffering from sickle cell anemia
Ss Heterozygous for the wild type beta-globin allele "Sickle cell trait"= carrier	NONE	HIGH	having one copy of the faulty gene boosts tolerance
ss Homozygous recessive for the wild type beta-globin allele	will develop sickle cell anemia	LOW (approximately 3%)	possessing two versions of the recessive allele leads to SCA and are highly prone to the lethal effects of malaria

* The term "heterozygote advantage" relevant when describing the sickle cell allele frequency maintained by malaria, since having a single copy of the faulty gene i.e being the carrier for sickle cell anemia can boosts your tolerance and can prevent the disease to get hold after being infected by malaria while being homozygous recessive for the faulty gene can make you highly prone to lethal effects of malaria.

*Natural selection did not remove sickle-cell allele from the population because it provides immunity against malaria and have higher relative fitness than either homozygous dominant or recessive phenotype of sickle-cell anemia