BIOLOGY 1M03 Lecture Notes - Lecture 25: Cystic Fibrosis, Effective Population Size, Vicia FabaPremium
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BIOLOGY 1M03 - Lecture 25 - Human Population Genetics (Continued)
● Effective population size is only the number giving birth to the new
● Hemoglobin variants include blood groups, such as Rh-negativity and Rh-
Positive have different tolerances against malaria.
○ The origin of these mutations is much older than the origin of malaria
so it didn’t evolve as a protection against malaria
● Thalassemia is a mutation where two copies gives a disease, one mutation
(heterozygosity) gives protection against malaria.
● Changes in metabolic enzymes can give rise to protection against malaria.
○ GP6D deficiency/favism (a digestive enzyme) is an X-linked gene.
Fava beans cannot be metabolized properly. Males suffer more from
this disease as a result. It arose 5-10K years ago. The question is,
why did this mutation arise not so late?
■ Agriculture arose around this time, and may be correlated with
● Duffy antigens, a genetic system, protect against vivax malaria.
● Cystic Fibrosis is most common in Europeans. There are about 4% carriers
(1/2500 diseased: 2pq=0.04, leading to q squared, which equals 0.0004)
● This lung disease is lethal: involves mucus build-up. There are ¼ chances of
death before 30, but was much higher previously.
● The mutated gene is cftr which changes chloride metabolism, which arose 50
○ Gene dating has only been known for ~20-25 years.
○ It was most likely not possible to have been a bottleneck to have
caused this mutation spread.
● To keep this mutation at 4% in the population might be attributed to
heterozygosity advantage, possibly from cholera (intestinal disease).
○ The cholera toxin promotes big rush of fluid into lower intestine.
Severe dehydration is a result, leading to death.
○ The spread may have been due to the First European cholera
epidemic in 1817.
○ What cholera does to flush water out of the body is involved in the
cholera metabolism. By tweaking it, the carriers have a higher chance
○ Possibly Typhoid?
○ It is an example of pleiotropy (multiple effects from one gene)
○ It happens too often to be explained by mutation selection balance
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