Human Genetics
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Human Genetics Application of Mendelian genetics to Human beings
Genetic Diseases
Autosomal recessive Sex-linked Chromosomal disorders
Sickle Cell Anemia: Autosomal recessive
Blood of affected individual has a reduced capacity for delivering oxygen to the tissues. Gene involved encodes information for making the hemoglobin molecule Hemoglobin is a protein that carries oxygen Hemoglobin gives blood the red color.
RBC
Normal= biconcave disk Travel through arteries, veins, capillaries People with sickle cell have normal cell shape if there is enough oxygen. One nucleotide is responsible for mutation.
Sickle cell
When oxygen levels are low, even slightly lower than normal, hemoglobin forms long insoluble strands RBC’s become long and thin like sickles Cells now cannot pass through narrow passages, clogging small capillaries Oxygen depletion (anemia), pain and tissue death
Two alleles for Sickle Cell anemia: HbA= normal hemoglobin HbS= Sickle cell Can you guess the homozygous for normal and homozygous for sickle cell? Heterozygous for sickle cell (carriers)= 1% demonstrate sickling Carriers show no symptoms of disease in normal circumstances Avoid strenuous exercise & high altitudes
Who is a carrier?
In the U.S. 1 out of 500 African Americans are carriers of sickle cell. In Africa 1 out of 100 are carriers. Why? The answer is related to another potentially fatal disease, malaria. Malaria is characterized by chills and fever, vomiting, and severe headaches. Anemia and death may result. Malaria is caused by a protozoan parasite (Plasmodium) that is transmitted to humans by the Anopheles mosquito.
Sickle cell is an adaptation
When malarial parasites invade the bloodstream, the red cells that contain defective hemoglobin become sickled and die, trapping the parasites inside them and reducing infection. Compared to AS heterozygotes, people with the AA genotype (normal hemoglobin) have a greater risk of dying from malaria. Death of AA homozygotes results in removal of A alleles from the gene pool. Individuals with the AS genotype do not develop sickle cell anemia and have less chance of contracting malaria. They are able to survive and reproduce in malaria-infected regions. Therefore, BOTH the A and S alleles of these people remain in the population.
Pedigrees
Establish familial inheritance patterns Cannot engineer crosses between two people like in Mendelian genetics What would happen if a woman who is a carrier for sickle cell anemia marries a man who is also a carrier had children?
Pedigrees
Circle=♀ Square= ♂ Horizontal line=Marriage Vertical line= children Bracket=siblings Shaded=person expresses the trait
Online resources What
is sickle cell anemia? Teen Health Genetic disease Genetics Home Reference
Genetic Diseases
Autosomal recessive Sex-linked Chromosomal disorders
Sickle Cell Anemia: Autosomal recessive
Blood of affected individual has a reduced capacity for delivering oxygen to the tissues. Gene involved encodes information for making the hemoglobin molecule Hemoglobin is a protein that carries oxygen Hemoglobin gives blood the red color.
RBC
Normal= biconcave disk Travel through arteries, veins, capillaries People with sickle cell have normal cell shape if there is enough oxygen. One nucleotide is responsible for mutation.
Sickle cell
When oxygen levels are low, even slightly lower than normal, hemoglobin forms long insoluble strands RBC’s become long and thin like sickles Cells now cannot pass through narrow passages, clogging small capillaries Oxygen depletion (anemia), pain and tissue death
Two alleles for Sickle Cell anemia: HbA= normal hemoglobin HbS= Sickle cell Can you guess the homozygous for normal and homozygous for sickle cell? Heterozygous for sickle cell (carriers)= 1% demonstrate sickling Carriers show no symptoms of disease in normal circumstances Avoid strenuous exercise & high altitudes
Who is a carrier?
In the U.S. 1 out of 500 African Americans are carriers of sickle cell. In Africa 1 out of 100 are carriers. Why? The answer is related to another potentially fatal disease, malaria. Malaria is characterized by chills and fever, vomiting, and severe headaches. Anemia and death may result. Malaria is caused by a protozoan parasite (Plasmodium) that is transmitted to humans by the Anopheles mosquito.
Sickle cell is an adaptation
When malarial parasites invade the bloodstream, the red cells that contain defective hemoglobin become sickled and die, trapping the parasites inside them and reducing infection. Compared to AS heterozygotes, people with the AA genotype (normal hemoglobin) have a greater risk of dying from malaria. Death of AA homozygotes results in removal of A alleles from the gene pool. Individuals with the AS genotype do not develop sickle cell anemia and have less chance of contracting malaria. They are able to survive and reproduce in malaria-infected regions. Therefore, BOTH the A and S alleles of these people remain in the population.
Pedigrees
Establish familial inheritance patterns Cannot engineer crosses between two people like in Mendelian genetics What would happen if a woman who is a carrier for sickle cell anemia marries a man who is also a carrier had children?
Pedigrees
Circle=♀ Square= ♂ Horizontal line=Marriage Vertical line= children Bracket=siblings Shaded=person expresses the trait
Online resources What
is sickle cell anemia? Teen Health Genetic disease Genetics Home Reference
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