Exam 2 - Anthropology Test 2 Interaction of mutation and...

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Anthropology Test 2 Interaction of mutation and natural selection. o Polymorphism : the situation in a species or population where there are 2 or more alleles of a gene, and at least 2 of the alleles have frequencies greater than or equal to 1 percent. The mutation rate for any gene is very low, so it cannot get an allele up to 1%, so something else has to be acting on the allele to reach the threshold of 1%. Polymorphism is explained by natural selection acting on mutations. In our species, approximately 28% of our genes are polymorphic. Lets say there are 30,000 genes in our genome and 28% are polymorphic. This means there are approximately 8,400 polymorphic genes. Genetic variability allows a species to go through natural selection and adapt. Example: A,B,O blood system: The genotypes are AA, A0, AB, BB, BO, and OO, and these produced proteins. The proteins that can be produced are A,A, A and B, B, B, and none for the OO. If you are a type A blood at birth, you have the anti-B antibody. This means it produces antibodies against the B protein. If you are type AB blood, you produce no antibodies. If you are type B blood, you produce antibodies against the A protein. If you are type OO blood, you produce antibodies against both A and B proteins. o Balanced Polymorphism : situation where there are 2 or more alleles of a gene in a population or species, and at least 2 of the alleles have frequencies equal to or greater than 1%, and the polymorphism is due to heterozygotes having a higher fitness (natural selective advantage) than both homozygotes. Example: Red blood cell variants and Malaria: Sickle Cell Allele o What is sickle cell ? Hemoglobin binds oxygen, and it is a protein that is comprised of 2 alpha and 2 beta polypeptide chains. Each alpha polypeptide chain has 141 amino acids, and each beta chain has 146 amino acids. Sickle cell is a result of a single point mutation affecting 1 amino acid. o Despite the expected intense natural selection against the sickle cell allele, the allele is maintained in high frequencies at polymorphic levels from 5-15% in some population. Malaria : o Malaria is caused by a parasite, which is transmitted from an infected individual to an unaffected individual by a mosquito. When it gets into your system, it gets into the red blood cells. Relationship between Sickle Cell Allele and Malaria o Evidence Geographical correlation between the distributions of polymorphic levels of the sickle cell allele and Malaria. Clinical and experimental studies show that individuals heterozygous for the sickle cell allele have a lower rate of malarial infection compared with individuals homozygous for “normal” hemoglobin. o
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This note was uploaded on 10/07/2011 for the course ANTH 1001 taught by Professor Tague during the Fall '07 term at LSU.

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Exam 2 - Anthropology Test 2 Interaction of mutation and...

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