L11 Variation II

Variation!-!II"

Dr. Gayle C Ferguson"[email protected]"

Douglas Futuyama, Evolution, Chapter 9"

Variation within populations"

Inbreeding depression"

Polymorphism "

Linkage "

Quantitative traits"

Inbreeding depression"Individuals are more likely to mate with relatives than non-

relatives - can be quite common in animals that live in groups""

Reduced survival and fecundity

Very important for conservation studies"

Golden lion tamarin"Highly endangered Brazilian monkey"

Offspring from captive breeding programmes being reintroduced to the wild (500 individuals, 140 zoos)" Fu

tuym

a EVOLUTION

2e,

Fig

ure

9.13!

Inbreeding is reduced by an elaborate out-crossing scheme"

Recessive lethal alleles come together in the homozygotes more often"

Cystic fibrosis inheritance"

Futu

yma EVOLUTION

2e,

Fig

ure

9.12!

Inbreeding depression in humans; the more closely related the parents, the higher the mortality rate among their offspring."The data are for offspring up to 21 years of age from marriages registered in 1903-1907 in Italian populations (from Stern, 1973)"


It can bring down a dynasty!"Inbreeding depression"

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Polymorphism "

Linkage "


Almost every individual in a sexually reproducing species is genetically unique!"

In humans 2 alleles/locus with 3000 polymorphic loci"

there are in all 101431 possible genotypes""

In comparison there are 1080 hydrogen atoms in the observable universe"""

How is this variation maintained? drift? selection?"""

Polymorphism"

Futu

yma EVOLUTION

2e,

Fig

ure

9.15!

An electrophoretic gel, showing genetic variation in the enzyme phosphoglucomutase among 18 individual killifishes. Five allozymes (alleles) can be distinguished by differences in mobility. The fastest, at top, is allele 1; the slowest, at bottom, is allele 5. Homozygotes display a single band, and heterozygotes two bands."



Polymorphism "

Linkage "


Linkage"Many traits including

morphological, physiological and behavioural features

exhibit polygenic variation"""

Such alleles are usually in “linkage

disequilibrium”."Knowing about A locus gives information about

B locus"""

Recombination during meiosis can break such linkage

disequilibrium"

Futu

yma EVOLUTION

2e,

Fig

ure

9.17!



Polymorphism "

Linkage "


Body size Running speed

Survival Fecundity"

Quantitative traits"When traits are continuous rather than discrete values "

e.g. eye colour"

and!when non-genetic factors come into play"

Futu

yma EVOLUTION

2e,

Fig

ure

9.20!

The frequency distribution of the number of dermal ridges, summed over all ten fingertips, in a sample of 825 British men."The distribution nearly fits a normal curve. The number of dermal ridges is an additively inherited polygenic character, with a heritability of about 0.95 (from Holt, 1955)"

Genotype x environment interaction"

Temperature affects the development of bristle number "differently for each genotype"

Genotypes differ in their reaction norms (variety of phenotypic "states that can be produced by one genotype)"

"


How to determine the source of variation here?"


Futu

yma EVOLUTION

2e,

Fig

ure

9.5!

Estimating heritability"

Vp = Vg + Ve Hence fraction of variation only due to genetic component"

h2 = Vg /Vp

Squared because it is a variance"

Futu

yma EVOLUTION

2e,

Fig

ure

9.23!

Variation between populations"

Geographic"

Gene flow"

Geographic"A gradual change in character or allele

frequency over geographic distance is called a cline!

Allopatric Sympatric Parapatric"

Bergmann’s rule pertaining to body size"

Futu

yma EVOLUTION

2e,

Fig

ure

9.28!

Again, is it due to the genotype or the environment?"

Geographic"

Futu

yma EVOLUTION

2e,

Fig

ure

9.29!

Variation between populations"

Geographic"

Gene flow"

Gene flow"Migration between neighbouring regions "

Inflow/outflow of genes between populations"

animal migrations, seeds, gametes, pollen, sperm (in marine environments)"

"Homogenisation results in one well-mixed population"

Futu

yma EVOLUTION

2e,

Fig

ure

9.30!

Can be severely limited by environmental conditions: wind patterns, ocean currents, geographic features"

Gene flow"

Futu

yma EVOLUTION

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Fig

ure

9.31!

Summary"

Populations harbour a lot of variation"e.g. at the DNA, protein or frequency level"

Many loci are naturally polymorphic "

Linkage disequilibrium between between alleles"can be reduced by recombination"

Quantitative traits: separation of genetic and phenotypic component, heritability and artificial selection"

'Between population variation’ is affected by geographical structuring

Gene flow reduces the effect of selection by mixing the populations"

L11 Variation II

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