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4 Mar 2011
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LECTURE 14 โ€“ March 3rd
Quantitative traits = complex traits
Variation in average differences in genotypes between individuals AND environmental
variation that gives phenotypic variation
Environmental variation because of food, climate, illnesses, etc.
Maristic traits โ€“ class of discrete traits
Discrete traits โ€“ either or traits; single-gene traits
MARISTIC TRAITS:
Whole-number range of values โ€“ possibilities are not infinite
Ex. number of progeny
Additive inheritance and incomplete dominance
๎€Additive gene action โ€“ in heterozygote, exactly intermediate of the two
homozygotes
oThis occurs with additive effects
๎€Incomplete dominance is example of additive gene action
oHeterozygote has trait value or state that is intermediate quantitatively
between the two homozygous classes โ€“ but NOT EXACTLY
INTERMEDIATE
oThis occurs because of environmental variation
Mutations in few genes โ€“ cause familial hypercolesteremia
๎€Still single-gene disease/disorder
๎€Because any one of the many genes is mutated can result in this
๎€Heterozygotes
๎€Blurring of lines
oGenotypically heterozygote but phenotypically homozygous can result
because of environmental influence
TODAYโ€™s lecture โ€“ quantitative trait analysis
Phenotype = E and genotype
How much is due to genetic variation?
Broad sense โ€“ extend of phenotypic variation that is attributed to genetic variation, all
types of genetic variation
๎€Can be quantified by Hsquared (representing broad sense)
๎€Vp = Vg + Ve
๎€Values range between 0 and 1
oThere is no env effect if 1 โ€“ all variation caused by genetic effects
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oMinimum is 0 โ€“ env effect is 100%
๎€BSH tells us
oHigh values suggest that the genotype is important in determining
whether this quantitative trait arises due to the segregation of particular
or specific alleles
oImportant in attributing whether this quantitive trait (hair colour,
weight)
oBUT NOT PREDICTIVE
๎€Canโ€™t take Hsquared and predict what the progeny will look like
based on the phenotype of the parents
Hsquared for some humans
๎€Height โ€“ pretty hight
oGenetic component
๎€Heart rate โ€“ at the middle โ€“ gen and env variation equal
What does BSH tell us?
๎€High โ€“ phenotype is likely to be attributed to its genotype within that family
oCannot extrapolate to other families, to other populations
oValues are specific to the family or the population
Why is BSH not predictive?
๎€Predicting genotype and phenotype of offspring is important, especially to plant
and animal breeders using artificial selection to enhance traits
oThey donโ€™t use BSH
๎€Look at the equation
oGenetic variation โ€“ types include additive effects, dominance effects,
epistatic effects
๎€I stands for interacting
๎€Epistatis โ€“ occurs when two genes or proteins are INTERACTING,
giving you another phenotype OR one locus masks effect of other
locus
๎€Genetic variation can be divided into 3 types ***
๎€To answer, examine V due to dominance effects
oCannot predict progeny accurately
oPlant breeders want to optimize specific traits
oDOMINANCE EFFECTS ARE NOT PREDICTIVE
oAs for epistatic variation,
๎€Recessive epistatis โ€“ R1 masking R2 allele
๎€Every generation, new dominance and epistatic relationships are
formed each generation
๎€So they are not predictive
๎€Passing on genotype, not alleles โ€“ these new combinations occur
generation to generation
oLeft with additive variation
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Document Summary

Variation in average differences in genotypes between individuals and environmental variation that gives phenotypic variation. Environmental variation because of food, climate, illnesses, etc. Discrete traits either or traits; single-gene traits. Whole-number range of values possibilities are not infinite. additive gene action in heterozygote, exactly intermediate of the two homozygotes: this occurs with additive effects. Incomplete dominance is example of additive gene action: heterozygote has trait value or state that is intermediate quantitatively between the two homozygous classes but not exactly. Intermediate: this occurs because of environmental variation. Mutations in few genes cause familial hypercolesteremia. because any one of the many genes is mutated can result in this. blurring of lines: genotypically heterozygote but phenotypically homozygous can result because of environmental influence. Broad sense extend of phenotypic variation that is attributed to genetic variation, all types of genetic variation. can be quantified by hsquared (representing broad sense)

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