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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
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
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
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.
- Winter '14