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Lecture 13

BIOC63Fall2013 Lecture 13 and 14.docx

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University of Toronto Scarborough
Biological Sciences
Karen Williams

BIOC63Fall2013 Lecture 13 and 14: Conservation Genetics Genetic diversity vs. Fitness  The more genetically diverse an individual is, the more fit for survival  positive correlation between individual fitness and genetic diversity Population fitness and population size  English primrose populations  the larger the population size the larger the offspring (cumulative cm)  Increased population size = increased genetic diversity = increased fitness What is conservation genetics?  Application of genetics to preserve species as dynamic entities capable of coping with environmental change (global warming, changing patterns of precipitation, invasive species etc.) Origin of Genetic Variation  Genetic variations comes from mutations = random DNA changes due to: 1. Spontaneous mutations  errors during mitosis and meiosis 2. Radiation  UV radiation can induce mutations 3. Viruses  their own DNA into cells 4. Mutagenic chemicals 5. Crossing over  secondary source of mutations – splicing of genes in different combinations and etc. may end up in a beneficial trait Effect of mutations  Most mutations are silent (neutral)  Many are deleterious  And only a few are advantageous Modification of Genetic Diversity  Crossing over  modified the original variation in the parents to a possible new one in the offspring  Genetic drift  chance loss of alleles in a population = DECREASE in variation  Gene flow  dispersal among populations (emigration decreases genetic variation and immigration increases it)  Non-random mating  unequal contributions to reproduction, may result from assortative mating (like mates with like) or female choice  Changes in population size  especially decrease in population Genetic diversity, the basics  Locus = location on chromosome where gene is  Gene has 2 or more versions (alleles)  Homozygous = same allele for a gene  Heterozygous = different alleles for the same gene Three fundamental  Within individual variation  loci, chromosomes, organism = heterozygosity (2 alleles at a given gene or locus)  Variation within a population  allele diversity and heterozygosity   Variation among populations  allele diversity and heterozygosity 1  Measurement of Genetic Diversity  H T H +PD PT  HT = total genetic diversity  HP = average within population diversity  DPT = is average divergence among populations Natural species genetic diversity   mean total heterozygosity varies across taxa  Mobile taxa have lower differences among populations, presumably due to increased gene flow  Biggest difference is due to how mobile individuals Genetic diversity: basis of evolution  With genetic variation in a population individuals with best genetic alleles leave most offspring  Increase of good alleles in next generation = survival of the fittest Genetic variation and Conservation Biology 1. Rate of evolutionary change in a population : proportional to amount of genetic diversity available  No variation in a population = population has low chance of adapting to changes in environment = higher chance of population going extinct  Peppered moth Example  under natural conditions, population made up of 2 months  peppered moth and melanic (darker so it is less hidden) 2  due to air pollution, bark turns darker so the melanic moth is now hidden and the other stands out so it falls pray to birds   1850-1970: air pollution, few tree lichens  most are melanic (first map)  recently: cleaner air, more tree lichen  melanic population dropped (2 ndmap)  if this moth did not come in 2 morphs (was less genetically varied) then the population might have gone extinct due to air pollution 2. Heterozygosity, or high genetic diversity, is positively related to fitness  two different alleles at a given gene or locus  2 to choose from and one may be better  if one allele is defective or bad, the other can still be functional, and the organism may still survive  heterozygosity and fitness components:  in trout  the greater the heterozygosity the increased the CF (condition factor = high CF  more fit)  clams  shell length increases with heterozygosity  oysters  O2 consumption decreases with heterozygosity  trout  less asymmetric traits with increased heterozygosity  elk  as heterozygosity increases, lifetime breeding success increases  butterflies  probability of extinction decreases as heterozygosity increases 3. Global pool of genetic diversity = total of genetic possibilitites  loss of diversity  decreased ability to respond to environmental change  populations of mountain here are adapted to different conditions (one lives south and one lives north)  With changing environmental climate, some of the individuals would survive better than others , but overall the species it self would not go extinct How is Genetic diversity assessed?  Multitude of different genetic markers  2 bands = heterozygous for that gene  How is population size measured?  Nc  census N = count all individuals  Ne  effective N = effective population size: N individuals in a population contributing genes to the next generation  commonly much smaller than Nc Reasons for Ne < Nc  Age structure: mature vs. immature  only some individuals are going to be adults that can mate  Sex ratio: often uneven  Unequal family size: you can have many small families, or a few large families, so you can have a lot of the adults mating or a few (big families = more related individuals)  Non-random mating  some of the males that can mate, DO NOT 3  Fluctuations in population size over time  environment and/or human induced Effect of sex ratio oneN  Ne = (4Nm x Nf)/ (Nm +Nf)  Nm and Nf  the number of breeding males and females  A) assume 500 mature adults, 50:50 sex ratio, random mating, equal reproductive success:  Ne = (4 x 250 x 250) / (250 + 250) = 500  often unrealistic because of dominance, and social structures  Example: gorillas  alpha males inseminates 100 females, while the beta males only sneak in one here and there so just because a male CAN mate, does not mean that he will because of the social structure of the pack  B) 1 male and 100 females, he mates with all of them  Ne = (4x100x1)/101 = 3.96  These 101 individuals are really the equivalent of almost 4 breeding individuals Genetic threats to small populations  Endangered species have small population sizes  Lower diversity in endangered species  For example: grey wolf = non endangered, diversity of 0.62 compared to Mexican wolf which is threatened and has diversity of 0.42   ex: English primrose  cumulative offspring size increases with population size   ex: Bighorn sheep 4   need an N of 101 or more in order to maintain the population Reasons for lower genetic variation in small populations  genetic drift  random loss of alleles (small populations have increased chance of having less genetic variance due either to o Founder effects  new populations founded by a few individuals   only subsample makes it to the sample o Bottleneck  mass mortality causes great reduce in population   Lower incidence of new mutations  Greater isolation (sometimes)  less gene flow among populations  genetic homogenization What is Genetic Drift?  Random change in frequency of an allele in a population over several generations   the smaller th
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