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Flashcards in population genetics detail Deck (42):
1

4 main factors which influence allele frequency distribution

natural selection, genetic drift, mutation and gene flow

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wha ar eeasurbale traits

quantitative traits

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quantitative traits

is a measurable phenotype that depends on the cumulative actions of many genes and the environment

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discontinuous traits

most traits are discontinuous e.. tongue roll/no tongue role

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traits that vary continuously are called

quantitative traits - height and wait

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continous variation

-no distinct categories -quantitative -controlled by lots of genes -strongly influenced by environment

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continuous traits are

controlled by lots of genes and the environment

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discontinuous variation

-distinct categories -controlled by a few genes -unaffected by the environment

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three reasons quantitative genetics is important

medicine agriculture conservation

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medicine and quantitative genetics

susceptibility to disease;; complex genetic and environmental interactions and understanding gents vs environmental causes 1) prevention 2) genetic counselling 3)genetically tailored treatment

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agriculture

economically important traits= quantitative traits. -basis for selective breeding programs -enviromental variation reduces efficiency of selection

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conservation

1)endangered species 2) captive breeding programs

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poly genic traits

Polygenic traits are those traits that are controlled by more than one gene. Such traits may even be controlled by genes located on entirely different chromosomes. Human height, eye and hair color are examples of polygenic traits. Skin color is another polygenic trait for humans and a variety of other animals.

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3 polygenic traits

metric- continous scale (height)

meristic- discrete scale (countable traits)

threshold- present or absent -all based on the assumption of normal distribution (affected/not effected)

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the there polygenic traits (metric, meristic and threshold) are based on

the assumption of normal distribution

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metric traits

e.g. height mean-centre of the phenotypic distribution

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Meristic traits

countable traits- can be sued to describe a particular species of fish or to identify an unknown species e.g. contain the bristol number on drosophila

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threshold traits

discrete phenotypes e.g. affected and unaffected -multifactoral e.g. alcoholic, alzheimers, cancer, diabetes, heart disease

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phenotype=

genotype and environment

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phenotypic variance equation

Vp=Vg +Ve +Vge

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Vp

phenotypic variance -total phenotypic variation of the segregating population

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Vg

genetic variation -genetic variation that contributes to the total phenotypic variation

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Ve

environmental variance -environmental contribution to the total phenotypic variation

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Vge

g x e interaction variance how far the environment and genes interact -variation associated with the genetic and environmental factor interactions

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therefore genetic variance =

Vg=Va + Vd +Vi

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Va

additive genetic variance - when a number of genes influence a genetic trait e.g. hair colour

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Vd

dominance genetic variance - phenotypic deviation caused by interactions b/w alternative alleles which control one trait

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Vi

interaction genetic variation -epistasis

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environmental variation is

stabilising

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mendelian inheritance patterns allow us to.

predict expected frequencies of alleles

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positive assortative mating

where organisms mate with others with similar character trait

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positive assortative mating causes

an increase in homozygous individuals a decrease in heterozygous individuals

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heritability of trait describes

how much variation is genetic

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two types of heritability

broad sense narrow sense

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heritability

measures the total genetic influence on phenotype --> considers additive genetics, dominance and epistatic

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broad sense heritability

 it tells you how much is related to the environment and how much is related to genetics

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narrow sense heritability

Narrow sense heritability is the proportion of total phenotypic variation that is due to the additive effects of genes. This component of variation is important because it is the only variation that natural selection can act on.

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H^2

H^2 should be between 0 and 1 -can vary widely across traits, environment and diff pop. -can be used to predict change in population mean under selection

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when H^2 increases..

the response to selection increases

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examples of heritability narrow sense

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measuring heritability

similarity between relative, compared to random individuals in population is one measure of H^2 pic

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measuring additive genetic effects:infinitesimal model

a simple model of inheritance of quantitative traits, which assumes an infinite number of unlinked loci, each with an infinitesimal (so large) effect. Infinite number of genes controlling phenotypic traits each with a very small effect