Changing Environments


Typical genetics deals with constant (or consistent) conditions

  • if there is selection,
    . . . -multiply the Hardy-Weinburg values by fitness, w = survival probability
    . . . . {AA, Aa, aa} = {wAA*p2, wAa*2pq, waa*q2}
  • since w is constant
    . . . -the same percentage survives every generation and
    . . . . with sufficient time, if wAA or waa is smallest of the w-values,
    . . . . that genotype will disappear from the population!

    Imagine a mutation that gives a tropical plant species the ability to withstand up to one hour exposure to minimum temperatures, and which occurs 10% of the time:

    n = 1
    exp
    F-1
    .81 .18 .01
    geno-
    type
    AA Aa aa
    min
    Temp
    32 oF 30 oF 28 oF
    w32 1.00 0.80 0.60
    w30 0.80 1.00 0.80
    w28 0.60 0.80 1.00

    In the 'normal' environment,
    where winter nighttime temperatures do not drop below 32 oF:
    n = 1
    geno-
    type
    AA Aa aa q
    w 1.00 0.80 0.60
    min
    Temp
    32 oF 30 oF 28 oF
    exp
    P-1
    810 180 10 0.100
    exp
    F-1
    810 144 6 0.081
    exp
    F-2
    844 119 3 0.065
    exp
    F-3
    874 96 2 0.051
    exp
    F-4
    899 78 1 0.041
    exp
    F-5
    919 62 1 0.033
    exp
    F-6
    935 50 0 0.025
    exp
    F-7
    949 39 0 0.020
    exp
    F-8
    960 30 0 0.015
    exp
    F-9
    969 23 0 0.012
    exp
    F-10
    976 18 0 0.009

    Starting with the P-1 generation {AA, Aa, aa} = {810, 180, 10}

  • if environment changed to winter nighttime temperatures drop to 28oF
    . . . q would rise as . . . . . . p declines
    . . . q approaches 1.00; . . . p approaches 0.00



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    © 2004 Prof. LaFrance, Ancilla College