Genotype frequency mutant allele less than 1 text

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Unformatted text preview: less than 1 % Text Monomorphic : gene with only one wild-type Text allele Polymorphic : gene with more than one wildtype allele 23 One gene may contribute to several visible characteristics Pleiotropy – Multiple phenotypic effects caused by a single gene Destruction of red blood cells Sickle cell syndrome: an example of pleiotropy Circulatory blockages Anemia Physical weakness Impaired mental function Kidney failure Damage to organs Spleen damage Heart failure Brain damage Paralysis 24 A variation on pleiotropy: Some alleles may cause lethality Some alleles may result not only in a visible phenotype, but also affect viability The assignment of dominant and recessive pertains only to the phenotype being regarded 25 Recessive lethal alleles - yellow coat heterozygouts. mutant allele is dominant to the wild type. F2 phenotypic ratio always 2:1 not 3:1 Homozygous AYAY die 26 Allele for yellow coat is dominant for coat colour, but recessive for lethality (recessive lethal allele) yellow allele is also related to obesity. Two heterozygotes for A+ and yellow (AY) produce only yellow and agouti offspring in 2:1 ratio 27 Do not assume the wild-type allele is always dominant! 28 Manx cats - spinal development Homozygous fetus dies in utero All Manx cats are heterozygous for the Manx allele heterozygouts have no tail. bred normal cat with manx, 50% will be manx Manx allele is dominant for taillessness and recessive for lethality (recessive lethal allele) 29 Both are examples of 1 allele affecting 2 different phenotypes (pleiotropy) -just because its dominant for one phenotype, does not mean it has to also be dominant for the others Aracauna breed chicken - 1 in 4 embryos die in the egg. they don’t have tails. but they have blue eggs 30 Mult...
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This document was uploaded on 02/25/2014.

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