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Human Biology
Course Code
Stephen Wright

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LECTURE January 27th
Extensions to Mendelian genetics
Law of segregation still held but geno-pheno relationship modified
Pleitropy, epistasis, etc. effects at one gene or MULTIPLE genes?
Independent assortment come into play with dihybrid crosses
Monohybrid crossing equal segregation
Always recessive always masked
Bateson did crosses
F1 new phenotype walnut
oIncomplete dominance perhaps????
Cannot self animals but cross F1 male with F1 female
oExpect in F2 1:2:1 ratio of walnut, rose, and pea
Single phenotype showed up a fourth!!
oCannot be accounted for because Mendel has 3 phenotypes
oCannot break down into one to two to one ratio
Saw numbers as nine to three to three to one ratio
oInstead of two genes influencing two different traits
oActually two genes influencing ONE phenotype
Cf. pleiotropy one gene with multiple phenotypes
oActually recover expected ratios good
oWalnut double heterozygote since parents were inbred lines
oTwo genes contributing to one phenotype but everything else fits with
Crucial cross to understanding
White crossed blue offspring
Crossed F1 white and blue result
To get blue, must have dominant phenotype at two genes
oAt least one big a and at least one big b
Otherwise, end up being white
These are mutants for the same phenotype but mutants from different genes
oSame gene cross white, get white
oDifferent gene combining them in f1, get blue phenotype
Think of it in genetic pathway
oKnock out function
oA gone no colour white phenotype
oB gone no colour white phenotype
oBoth knocked out white phenotype
Complementation cross two mutants and recover the wild type in f1
oTo get blue both genes must be functional
oRight hand mutation in gene 2
oCrossing mutants
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