Anthropology Test 2
Interaction of mutation and natural selection.
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.
variability allows a species to go through natural selection and adapt.
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
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.
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.
Red blood cell variants and Malaria:
Sickle Cell Allele
What is sickle cell
? Hemoglobin binds oxygen, and it is a protein that is
comprised of 2 alpha and 2 beta polypeptide chains.
polypeptide chain has 141 amino acids, and each beta chain has 146
is a result of a single point mutation affecting 1
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 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
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