Table of Contents
- 1 How does natural selection affect sickle cell anemia?
- 2 Why do people with sickle cell anemia have a selective advantage in areas where malaria is present?
- 3 How do diseases affect natural selection?
- 4 What was Dr Allison’s initial observations?
- 5 Why would a harmful allele be maintained in a population?
- 6 Why has natural selection not eliminated Huntington’s disease?
- 7 How are red blood cells maintained by natural selection?
- 8 Why are people with sickle cell anemia protected?
How does natural selection affect sickle cell anemia?
Heterozygotes (AS) with the sickle-cell allele are resistant to malaria. Therefore, they are more likely to survive and reproduce. This keeps the S allele in the gene pool….Sickle Cell and Natural Selection.
| Genotype | Phenotype | Fitness |
|---|---|---|
| AA | 100% normal hemoglobin | Somewhat reduced fitness because of no resistance to malaria |
Why do people with sickle cell anemia have a selective advantage in areas where malaria is present?
D. In areas where the malaria parasite is present, individuals who are heterozygous for the sickle cell allele are at a selective advantage because they are protected against malaria but do not get sickle cell disease.
Is Sickle Cell Anemia stabilizing selection?
Stabilizing selection – In this type the population stabilizes on a single non-extreme trait. It is the most common type of natural selection. It results in the decrease of population’s genetic variation. This type balances the two traits as in sickle cell anaemia which has two alleles.
Why natural selection did not remove the sickle cell allele from the population?
They may be maintained by heterozygote advantage When carrying two copies of an allele is disadvantageous, but carrying only one copy is advantageous, natural selection will not remove the allele from the population — the advantage conferred in its heterozygous state keeps the allele around.
How do diseases affect natural selection?
From an evolutionary perspective, infectious diseases have probably been the primary agent of natural selection over the past 5000 years, eliminating human hosts who were more susceptible to disease and sparing those who were more resistant.
What was Dr Allison’s initial observations?
What were Dr. Allison’s initial questions when he went to East Africa in 1949? distribution of the ABO blood groups and other inherited characteristics, including the sickle cell allele, in East African tribes.
What can you do to avoid getting sickle cell?
Prevention of sickle cell disease symptoms
- Drink plenty of water.
- Avoid extremely hot or cold temperatures.
- Avoid places or situations with low oxygen, such as high altitudes.
- Avoid strenuous exercise or athletic training.
- Get plenty of rest and take frequent breaks during exercise.
- Take the medicine hydroxyurea.
Why hasnt natural selection eliminated sickle cell anemia?
Natural selection cannot completely eliminate the gene that causes this disease because new mutations arise relatively frequently — in perhaps 1 in 4000 gametes. The allele may be common, and not deleterious, in a nearby habitat.
Why would a harmful allele be maintained in a population?
Deleterious alleles may also be maintained because of linkage to beneficial alleles. The inability of natural selection to eliminate diseases of aging is a reminder that fitness — success in producing progeny, or in contributing genes to the population gene pool — is not equivalent to the absence of disease.
Why has natural selection not eliminated Huntington’s disease?
In general, Huntington’s is rare — 30-70 cases per million people in most Western countries — but it is not entirely eliminated because selection does a relatively poor job of weeding these alleles out, while mutation continues creating new ones.
Why does selection favor the sickle cell allele?
Stabilizing selection (also called balancing selection) is thus acting on the sickle-cell allele: (1) Selection tends to eliminate the sickle-cell allele because of its lethal effects on homozygous individuals, and (2) selection tends to favor the sicklecell allele because it protects heterozygotes from malaria.
Why is sickle cell anemia less common in African Americans?
As a result, the selection against the sickle-cell allele in America is not counterbalanced by any advantage, and the allele has become far less common among African Americans than among native Africans in Central Africa. Stabilizing selection is thought to have influenced many other human genes in a similar fashion.
How are red blood cells maintained by natural selection?
Normal red blood cells (top) and sickle cells (bottom) They may be maintained by heterozygote advantage When carrying two copies of an allele is disadvantageous, but carrying only one copy is advantageous, natural selection will not remove the allele from the population — the advantage conferred in its heterozygous state keeps the allele around.
Why are people with sickle cell anemia protected?
People that are heterozygous for the cf allele are protected from the dehydration caused by cholera, and the cf allele may provide protection against typhoid fever too.