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    Gene Flow + Migration

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    Gene flow occurs when genes from one population migrate into another population through the movement of individuals and gametes. This helps equalize allele frequencies between populations and introduces new alleles, but also erodes genetic differences caused by local adaptation. The level of gene flow is measured by metrics like migration rate and migration variance, with higher values indicating faster homogenization of populations. While gene flow counters genetic divergence between populations, natural selection can also act to maintain differences under certain conditions.

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    Gene Flow + Migration

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    Gene flow occurs when genes from one population migrate into another population through the movement of individuals and gametes. This helps equalize allele frequencies between populations and introduces new alleles, but also erodes genetic differences caused by local adaptation. The level of gene flow is measured by metrics like migration rate and migration variance, with higher values indicating faster homogenization of populations. While gene flow counters genetic divergence between populations, natural selection can also act to maintain differences under certain conditions.

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    Gene flow occurs when genes from one population migrate into another population through the movement of individuals and gametes. This helps equalize allele frequencies between populations and introduces new alleles, but also erodes genetic differences caused by local adaptation. The level of gene flow is measured by metrics like migration rate and migration variance, with higher values indicating faster homogenization of populations. While gene flow counters genetic divergence between populations, natural selection can also act to maintain differences under certain conditions.

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    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    25 views2 pages

    Gene Flow + Migration

    Uploaded by

    random acc
    Gene flow occurs when genes from one population migrate into another population through the movement of individuals and gametes. This helps equalize allele frequencies between populations and introduces new alleles, but also erodes genetic differences caused by local adaptation. The level of gene flow is measured by metrics like migration rate and migration variance, with higher values indicating faster homogenization of populations. While gene flow counters genetic divergence between populations, natural selection can also act to maintain differences under certain conditions.

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    of 2

    GENE FLOW & MIGRATION

    White Clover (Trifolium repens)


    − CYP79D15 gene (cyanide-production)
     negative temperatures − plants do not produce cyanide
     low temperatures − plants produce cyanide

    I. PATTERNS IN SPACE
     Cline
    → gradual (smooth) change in an allele frequency or in the mean of a character over a
    geographical transect
    → can extend over large geographical scales or can be much shorter
    → product of local adaptation
     organisms evolve to be more well-suited to its local environment than other
    members of the same species
    → example:
    o altitudinal cline − yarrow plants mean height in different local populations
    o latitudinal cline − moose (Alces alces) average body mass in Sweden

     Gene Flow
    → incorporation of genes into a gene pool of one population from one or more other
    populations
    → erodes the differences in genes caused by selection and drift (balance)
    → gene pool − totality of genes of a given interbreeding population

    II. ROLES OF GENE FLOW IN EVOLUTION


    i. equalizes allele frequency
    − erode genetic differences between populations
    − may promote Hardy-Weinberg Equilibrium
    ii. introduces new alleles into a new population
    − gene flow, like mutation, equalizes alleles
    iii. results from dispersal of individuals and their gametes
     passive − move place to place with assistance (e.g., plants)
     active − move place to place without assistance (e.g., animals)

    III. MIGRATION VS. GENE FLOW


    • Evolutionary Biologists: synonym of gene flow
    • Other context: directed large-scale movements of organism; do not necessarily result in gene flow

    IV. HOW IS GENE FLOW MEASURED


    a. discrete or patchy populations (e.g., islands & mountain tops)
     Migration Rate (m) − fraction of individuals that immigrated from one to another population
    within the current generation
    → example: 1000 individuals in a population with 120 immigrants
    𝑛𝑛𝑛𝑛. 𝑜𝑜𝑜𝑜 𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖
     𝑚𝑚 = | m = 0.12
    𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝
      m = quicker genetic differences are erased
    b. spatially continuous populations
     Migration Variance (σm2) − square root of the mean of the squared distances (birth places
    of mother and their offspring)
    → example: Sceloporus olivaceus
     σm2 = 9800 m2 | σm = 99 m
      σm2 = quicker genetic differences are erased
    GENE FLOW & MIGRATION

    V. GENETIC DIVERGENCE BETWEEN POPULATIONS


     Genetic Divergence − gradual accumulation of difference in gene pools of genetically separated
    populations (physical/biological barriers)
    → natural selection, genetic drift, mutation can contribute to divergence
    → countered by genetic flow
     FST - statistic used to describe genetic divergence between 2 or more populations
    → if the FST is 0: populations are genetically identical
    → if the FST is 1: population is fixed for a different allele
     many species with broad geographic ranges
    → FST increase with the distance between 2 populations
    → pattern called isolation-by-distance

    VI. GENE FLOW & SELECTION


     both gene flow & local selection at work  allele frequencies evolve
     gene flow is weak relative to selection
    → allele frequencies evolve to what selection favors
     gene flow is strong relative to selection
    → gene swamping − genetic drift overwhelms local adaptation
    → allele frequencies equalize
     selection can also maintain differences, if it’s acting in all population

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