Biology 4250 Evolutionary Genetics

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Biology 4250 Evolutionary Genetics

• Dr. David Innes
• Dr. Dawn Marshall
• Lab. Monday Feb. 5
• Room SN-2092

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Outline of topics 1. Introduction/History of
Interest in Genetic Variation (Ch. 1,2) 2. Types
of Molecular Markers (Ch. 3) 3. Molecular
Evolution (Ch. 4) 4. Individuality and
Relatedness (Ch. 5) 5. Population Demography,
Structure Phylogeography (Ch. 6) 6.
Phylogenetic Methods Species Level Phylogenies
(Ch. 8) 7. Speciation, Hybridization and
Introgression (Ch. 7) 8. Sex and Evolution (Ch.
5) 9. Forensic Applications (Ch. 5) 10. Human
Evolutionary Genetics 11. Conservation Genetics
(Ch. 9)
Background
Applications
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Individuality and Parentage

• Human Forensics
• Ramets and Genets (sexual and asexual)
• Genetic chimeras
• Gender ascertainment
• Genetic parentage

More detail
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Individuality and Parentage

• Sexual reproduction genetic variation large
• amount of genotypic variation
• - every individual in a population
  genetically
• unique

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Genetic Consequences

• Sexual high genotypic diversity
• Asexual low genotypic diversity
• Mixtures intermediate diversity
• Genetic markers ? used to infer mode of
• reproduction

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Detecting Asexual Reproduction

• Population sample
• (a) deviation from HWE
• (b) association among loci
• (c) genotypic diversity
• (d) combined analysis
• 2. Compare offspring and mother genotypes

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Detecting Asexual Reproduction

• Examples
• 1. Seaweed (Enteromorpha linza)
• 2. Dwarf Birch (Betula glandulosa)
• 3. Moss (Polytrichum juniperinum)
• 4. Water Flea (Daphnia pulex)

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Mode of Reproduction
Sexual
Asexual
Fixed Heterozygotes
22 MLG
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Detecting Asexual
1. Number of MLG (Clones) 2. GDR genotypic
diversity ratio 3. log p from a X2 for
HWE p 0.05 1.3 p 0.0001 4.0
FP- sexual
OP- asexual
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Other Asexual Invertebrates
Sea stars fission sexual recruitment Corals
fission, fragmentation - asexual
planula larvae - sex Sea anemones
fission, planula larvae, clones
distributed 100s of km -variation in
sex/asex among species
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Asexual Vertebrates
Whiptail lizard
Parthenogenetic clones derived from hybrids
between sexual species (often polyploid)
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Asexual Vertebrates
Avise (2005) Fig. 5.4 Parthenogenesis
Gynogenesis Hybridogenesis
Poeciliopsis
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Age of Clones

• clonal genotypes ecologically successful
• expect clonal genotypes to be short lived
• - lack of recombination (evolutionary
  potential)
• - accumulation of deleterious mutations
  (Mullers
• 
  Ratchet)
• Asexual taxa ? recent origin
• Exceptions? ? Bdelloid rotifers
• 360 spp.
  No males

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Mullers Ratchet Stochastic loss of least loaded
clone Mutation genetic load always increasing
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Meselson Effect

• Diploid asexuals
• - no recombination
• - alleles at each locus should diverge
  over
• 
  time

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• Method
• Sequence alleles of a gene in asexual and sexual
  species
• Count frequency of synonymous substitutions

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Sexual
Asexual
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Clonal Microorganisms

• Protozoa, Bacteria, Fungi
• agents of human disease
• asexual strains with particular medical
• characteristics
• sex and recombination new strains
• (resistance and virulence)

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Bacteria (E. coli)

• Genetic markers allozymes, DNA
• - limited of MLG
• - some MLG widespread
  geographically
• unassociated hosts
• Conclusion
• - reproduction clonal, occasional
  sex
• - periodic selection sequential
  replacement
• by genotypes with high fitness

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Genetic Chimeras

• High degrees of IGH, i.e. many different genetic
  lineages within an individual, have been detected
  in a number of different types of organisms.
  Thomson et al. (1991) sampled leaves from
  strangler fig trees (211 per tree) from several
  branches in 14 individuals of six species of
  figs. Thirteen of the individual trees (all
  species) showed multiple genotypes (28
  genotypes), including the trees where only two
  leaves had been sampled. All in all the 14 trees
  represented at least 45 genetic individuals.
• (IGH) intraorganismal genetic
• heterogeneity

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Genetic Chimeras
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Gender Ascertainment

• Use of genetic markers to identify males and
• females in non-dimorphic species
• - Determine sex in early life history stages
• - Data for studies on
• sex ratio, sexual selection
• Chromosomal sex determination
• XX XY ZZ ZW

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Gender Ascertainment
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Gender Ascertainment
Overall, selection on fledgling viability on the
basis of morphological traits and hatching date
was not confounded by an individual's gender.
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Individuality and Parentage

• Human Forensics
• Ramets and Genets (sexual and asexual)
• Genetic chimeras
• Gender ascertainment
• Genetic parentage