Biology 1201A Lecture Notes - Lecture 10: Heterozygote Advantage, Sickle-Cell Disease, Allele Frequency

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14 Mar 2016

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Heterozygote advantage (over dominance) selecion in which the heterozygous phenotype has the highest itness. The phenotype associated with the heterozygote has the highest itness. The selecion pressure has to be able to disinguish between the homozygote and heterozygote there for it has to be co-dominant or incomplete dominance. Sickle cell anemia the protein doesn"t shape the blood cell properly. Hemoglobin is very important to carry the oxygen but when they are sickled they aren"t as good at carrying the oxygen. In some countries this can cause increased risk for mortality. Heterozygotes have some normal and some sickled red blood cells: sill have some diiculies but not to the extent that homozygous sickle has. In canada there"s no advantage of being heterozygous. If you are homozygous normal, then you have a high chance of geing malaria. But if you are homozygous sickle then your itness is sill lowered because you have sickle cell anemia but won"t get malaria.

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QUESTION 15 (8 points)

Sickle-cell anemia is an interesting genetic disease. Normal homozygous individuals (SS) have normal blood cells that are easily infected with the malarial parasite. Individuals homozygous for the sickle-cell trait (ss) have red blood cells that readily collapse when deoxygenated. Although malaria cannot grow in these red blood cells, individuals often die because of the genetic defect. However, individuals with the heterozygous condition (Ss) have some sickling of red blood cells, but generally not enough to cause mortality. In addition, malaria cannot survive well within these "partially defective" red blood cells. Thus, heterozygotes tend to survive better than either of the homozygous conditions. If 9% of an African population is born with a severe form of sickle-cell anemia (ss), what percentage of the population will be more resistant to malaria because they are heterozygous (Ss) for the sickle-cell gene?

Questions 4-6. Sickle cell disease:
Sickle cell disease (sickle cell anemia) is a relatively common disorder in individuals of

African descent and affects approximately 1 in 500 African-Americans. Due to a mutation in an autosomal gene for hemoglobin, the homozygous recessive genotype leads to red blood cells that are relatively stiff and sticky, and deform into a sickle shape as they lose oxygen. This leads to problems in the spleen, and anemia.

There are hundreds of different hemoglobin alleles. Individuals heterozygous for the sickle cell allele and one non-sickle cell allele usually do not experience major complications or even noticeable symptoms. A genetic test is available to diagnose carriers.

James does not have sickle cell disease, neither does his mother or father, but his sister does. His wife Natasha does not have sickle cell disease, and neither of her parents does either. Natasha also has a sister who has sickle cell anemia and two brothers without the disease.

5.) If James and Natasha have a child, what is the probability that the child would be a homozygote for the recessive allele and have sickle cell disease? You may draw the Punnet square but please solve the problem using probability calculations, then explain your reasoning in 2-5 complete sentences.

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Sickle-cell anemia is an interesting genetic disease. Normal homozygous individuals (SS) have normal blood cells that are easily infected with the malarial parasite. Thus, many of these individuals become very ill from the parasite and many die. Individuals homozygous for the sickle-cell trait (ss) have red blood cells that readily collapse when deoxygenated. Although malaria cannot grow in these red blood cells, individuals often die because of the genetic defect. However, individuals with the heterozygous condition (Ss) have some sickling of red blood cells, but generally not enough to cause mortality. In addition, malaria cannot survive well within these "partially defective" red blood cells. Thus, heterozygotes tend to survive better than either of the homozygous conditions. Assuming an African-American child were born each day of the year, statistically, one of these children per year would have a severe form of sickle-cell anemia (ss). Assuming Hardy-Weinberg equilibrium of these alleles, what is the percentage of the African-American population that are sickle-cell carriers? (Note that these carriers will turn out to be more resistant to malaria, should they decide to visit a malaria-infested part of the world; sometimes there are bizarre perks to being a carrier of a horrible disease!). Enter a percentage number (round up to whole number) without percent sign (%)

Biology 1201A Lecture Notes - Lecture 10: Heterozygote Advantage, Sickle-Cell Disease, Allele Frequency

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