Relationship exhibited by different alleles does not

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Unformatted text preview: ferent alleles does not affect the way they are transmitted. Rather, it is a reflection of the way in which the proteins they encode act in the cell. 16 A gene may have more than two alleles Multiple alleles exist for ALL genes e.g., blood type : A (IA), B (IB), O (i) e.g., trait of lentil seed coat pattern: spotted, dotted, clear (no pattern), marble-1 or marble-2 e.g., drosophila eye colours white, red, or eosin e.g., mouse coat colour black, black and tan, or agouti e.g., rabbit coat colour agouti, albino, chinchilla, himalayan 17 A gene may have more than two alleles Reciprocal crosses can be conducted between purebreeding lines representing all phenotypes, to establish the dominance relationships between all possible pairs of alleles. This reveals a dominance series, in which alleles are listed in order from dominant to recessive. when dealing with multiple alleles, the wild-type allele is designated with a superscript A+, anything without the plus is not a wildtype, and is mutant. Text 18 A dominance series: Four alleles for coat pattern recessive to everything Superscript + donates wild-type allele 19 Crosses using homozygotes to establish dominance series 20 many mutant alleles found for coat colour ChCh = recessive cc = recessive C+_= wild-type •  albino killed by predation in wild •  in nature c+ has a frequency of > 99% •  c+ is a monomorphic gene Genotype Phenotype c+_ Wild type chch Himalayan cc Albino 21 New alleles arise through mutation Chance alterations in the genetic material arise spontaneously in nature Wild-type allele A1 A2 Mutant alleles A3 Site of mutation (change in DNA sequence) just cause something is happening at genetic level, doesn’t mean it will occur at phenotype level 22 Allele frequency The percentage of the total number of copies of a gene in a population represented by a particular allele Wild-type allele : greater than 1 % any allele found at a frequency of greater than 1% in the population - not phenotype frequency. genotype frequency Mutant allele :...
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This document was uploaded on 02/25/2014.

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