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Population Genetics (Case Study) Fitness types, 2.Heterozygous Advantage…
Population Genetics (Case Study) Fitness types
Recessive Lethal
What is it ? - An inheritance that the allele is only lethal in homozygous from (aa); if it is in heterozygous form (Aa), the allele appears to be normal
Example: Cystic Fibrosis (CF)
Concept: - CF is an inherited disorder- causes damage to lung, digestive system and other part
How it works ?
In people with CF, a defective gene causes the secreted fluid like mucus to become sticky and thick. So this will plug up tubes, ducts and passageway instead of acting as lubricants in the body
People with CF has both copy of Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene that contain mutations from parents
Person that only has one copy of CFTR gene considered as carrier, they do not have the disease but the can pass on the gene to their progeny
Heterozygous Disadvantages (Underdominance)
Example: Maternal-Fetal Incompatibility Rh Blood Group
Incompatibility between maternal anf foetus can cause fetal mortality because antibody production will destroys red blood cells of the foetus.
Happen where the mother is Rh- (rr) and the father is Rh+ (RR or Rr). Allele R indicates the presence of antigen D from gene RHD and allele r is the absence of antigen D.
In the mating rr x RR, all offsprings are incompatible with the mother, so the selection towards these infants will be greater when compared to rr x Rr, where only half of the progeny are incompatible.
Selection only occur in heterozygotes so that we can predict unstable equilibrium.
(definition)
2.Heterozygous Advantage (Overdominance)
Example 2: Drosophila eye colour :explode:
Two types of Drosophila eye colour was observed in the initial population: White eyes ww and wild type w+w+, which both were said to be poor in producing pigments. Surprisingly, once these two genotypes were crossed, the resulting ww+ is produces more pigments than both in previous generation. Hence, it is selected.
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