Variety of mating systems
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Variety of mating systems. Panmixia Assortative mating Disassortative mating Outcrossing Inbreeding Mixed mating. Disassortative mating. What is the equilibrium frequency of alleles S1, S2, S3, and S4? What is the fate of a new mutation that produces allele S5?. Inbreeding.

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Variety of mating systems
Variety of mating systems

  • Panmixia

  • Assortative mating

  • Disassortative mating

  • Outcrossing

  • Inbreeding

  • Mixed mating


Disassortative mating
Disassortative mating

What is the equilibrium frequency of alleles S1, S2, S3, and S4?

What is the fate of a new mutation that produces allele S5?


Inbreeding
Inbreeding

What is inbreeding?

Forms of inbreeding


Genetic consequences of inbreeding
Genetic consequences of inbreeding

Loss of heterozygosity

Do allele frequencies change (i.e., does inbreeding result in evolution)?


Genetic consequences of inbreeding1
Genetic consequences of inbreeding

Heterozygosity:

Homozygosity:

Genetic variance within lines:

Genetic variance among lines:

Response to selection among lines:

Fitness of inbred lines:


The inbreeding coefficient wright s f
The inbreeding coefficient, Wright’s F

Sewall Wright

1889-1988


The inbreeding coefficient wright s f1
The inbreeding coefficient, Wright’s F

F ranges from 0-1

  • 0 = completely outbred (H-W)

  • 1 = completely inbred (homozygous)

    F can be thought of as:

  • Proportional loss of heterozygosity

  • Probability of homozygosity

  • Half the coefficient of relatedness of the parents

    F is measured relative to some starting population, which is usually assumed to have F = 0


The inbreeding coefficient wright s f2
The inbreeding coefficient, Wright’s F

From Hartl and Clark Fig. 4.15


Genotype frequencies as a function of f
Genotype frequencies as a function of F

AA: p2 + pqF

Aa: 2pq - 2pqF

aa: q2 + pqF


How can f be estimated if we don t have a pedigree for the whole population
How can F be estimated if we don’t have a pedigree for the whole population?

HI = observed heterozygosity at neutral loci (usually with molecular markers)

HT = heterozygosity expected under H-W (2pq)

Aa: 2pq - 2pqF = HI

2pq(1-F) = HI

HT(1-F) = HI

F = 1-(HI/HT)

F = (HT-HI)/HT


Inbreeding depression
Inbreeding depression

What is inbreeding depression?

What causes inbreeding depression?

How do organisms avoid inbreeding depression?


Inbreeding1
Inbreeding

Scientists find no biological reason to stop first cousins from marrying

  • Risks to children born to cousins not as high as previously thought

    By Denise Grady

    The New York Times

    Thursday, April 4, 2002

Sarah

Wedgwood

Josiah

Wedgwood I

Robert

Darwin

Susannah

Wedgwood

Josiah

Wedgwood II

Mrs.

JWII

Charles

Darwin

Emma

Wedgwood


Is inbreeding always bad
Is inbreeding always bad?

By exposing recessive alleles to selection in homozygotes:

  • Leads to rapid fixation of beneficial recessive alleles

  • Purges deleterious recessives; aka, lightens the genetic load