BIOA01H3 Lecture Notes - Lecture 28: Sickle-Cell Disease, Hypercholesterolemia, Hemoglobin

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19 Nov 2014

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Bioa01h3: life on earth unifying principles lecture 28: human traits. Incomplete dominance in human traits: sickle-cell disease: homozygote recessive has sickle-cell disease, heterozygote has milder sickle-cell trait, familial hypercholesterolemia: homozygote has severe form of disease; heterozygote has mild form of disease. Sickle cell anaemia: a mutation in the gene coding for beta haemoglobin reduces the ability of the red blood cells to carry oxygen, people with sickle cell anaemia are homozygous for the recessive hb-s allele. Multiple alleles: three or more alleles for a gene: found among all individuals in a population, diploid individuals only have two of the alleles, phenotype depends on relationship between alleles. Pleiotrophy: the condition in which single genes affect more than one character of an organism eg. sickle cell anemia.

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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.

cyanalligator893

A human gene called the Î²-globin gene encodes a polypeptide that functions as a subunit of the protein known as hemoglobin. Hemoglobin is found within red blood cells; it carries oxygen. In human populations the Î²-globin gene can be found as the common allele known as Hb^A, and it can also be as the Hb^S allele. Individuals who have two copies of the Hb^S allele have the disease called sickle cell disease. Are the following examples descriptions of genetics at the molecular, cellular, organism, or population level?

A. The Hb^Sallele encodes a polypeptide that functions slightly differently from the polypeptide encoded by the Hb^Aallele.

B. If an individual has two copies of the Hb^Sallele, that persons red blood cells take on a sickle cell shape.

C. Individuals who have two copies of the Hb^Aallele do not have sickle cell disease, but are not resistant to malaria. People who have one Hb^Aallele and one Hb^S allele do not have sickle cell disease but are resistant to malaria. People who have two copies of the Hb^Sallele have sickle cell disease, and this disease may significantly shorten their lives.

D. Individuals with sickle cell disease have anemia because their red blood cells are easily destroyed by the body.

rosewhale208

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?

BIOA01H3 Lecture Notes - Lecture 28: Sickle-Cell Disease, Hypercholesterolemia, Hemoglobin

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