Answer:
D
Explanation:
A. If a genetic disease reduces fertility and the allele that causes the disease offers no other advantage, the allele will likely eventually disappear, due to natural selection.
This is true. If the disease reduces fertility, the likelihood of the affected individual passing it on to children is decreased. If there is no fitness advantage, it will slowly be reduced in the population by chance, because natural selection is not acting positively upon it
B. Natural selection does not favor individuals who are homozygous for the sickle-cell allele, because these individuals typically die before they are old enough to reproduce.
This is true, individuals carrying two copies of the sickle cell allele might be more resistant to malaria, but they also have a range of health problems that often cause early mortality or severely reduced quality of life, cancelling out the beneficial features of this allele.
C. Individuals who are heterozygous HbA/HbS are protected from malaria, and this is why sickle-cell disease persists in wetter, mosquito-ridden regions in Africa.
This is true. Malaria persists in certain regions of Africa because the conditions are favourable for the mosquito that carries the disease. The heterozygous HbA/HbS genotype is prevalent in African population because it protects individuals from malaria, giving them a fitness advantage. Therefore, the natural selection acts positively upon the sickle cell allele in these areas, and over time, it becomes more prevalent
D. In regions where malaria does not occur, individuals who are heterozygous HbA/HbS have a fitness advantage over those who are homozygous for the normal hemoglobin allele (HbA).
This is false. Without the selection pressure of malaria, there is no advantage of having a copy of the sickle cell allele over the normal allele.
In regions where malaria does not occur, individuals who are heterozygous
HbA/HbS have a fitness advantage over those who are hom ozygous for the
normal hemoglobin allele (HbA) is False.
The individuals who have heterozygous HbA/HbS only have an advantage in the aspect of malaria as it makes them less susceptible to the disease.
This is the only advantage it offers and it doesn't offer any special advantage
such as more fitness or increase in fertility.
Individuals with sickle cell die early thereby preventing natural selection as
they are mostly unable to reproduce before death.
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