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Genes Within Populations - Coggle Diagram

- - - - can be altered via natural selection, repeated mutations, incoming migrants, or simply by chance
    - - study of genetic variation within a population
- - - - no mutation takes place
      - no genes are transferred to or from other sources
      - mating is random
      - very large population size
      - no selection favoring one genotype over another occurs
      - assumes the original proportions of the genotypes in a population will remain constant if these 5 criteria are met
- - - - phenotypically similar individuals mate
      - causes frequencies of particular genotypes to differ greatly from those predicted by the H-W principle
      - does not change reproductive success, but changes with whom they mate
    - - phenotypically different individuals mate, produces an excess of heterozygotes
  - - - allele frequencies from the founding individuals are different from the population they came from
      - some individuals disperse and become founders of a new, isolated population
    - - mass population wipe, the few individuals remaining represent only a small portion of the original population's gene pool
      - even if population size rebounds, there is significantly less genetic variability
  - - - variation among individuals must result in differences in the number of offspring surviving in the next gen
      - phenotypic variation must have a genetic basis (if everybody has the same genes, the offspring will still all be the same)
      - phenotypic variation must exist among individuals in a population (no variation = no natural selection)
    - - genetic changes that decrease the probability of capture by a predator (ex. camoflauge)
    - - enzyme alleles; enzymes formed by these alleles function differently at different temperatures
    - - alleles that decrease uptake of insecticide, decrease # of target sites, enhance ability of enzymes to locate and detoxify insecticide molecules
- - - - energy + time each sex invests in producing and rearing offspring
      - females generally have a higher parental investment (eggs are larger, female mammals usually responsible for gestation and lactation)
    - - reproductive events are less expensive for males; they increase fitness by mating with as many females as possible
      - reproductive events are more costly for females; # of eggs limits success so they are choosy
  - - - competition for mates
      - ex. secondary sexual characteristics: peacock tail feathers, ram's horns
    - - competition between members of one sex (usually males)
      - occurs in areas where females feed/bear young, sometimes males compete with each other
    - - mate choice (the power to charm)
      - direct benefits
        
        for species where males help raise young, females can benefit by choosing a mate that provides the best care (the better the parent, the more offspring); in species where men provide territory/food/refuge, females benefit by being able to feed w/o disturbance
      - indirect benefits
        
        could lead to higher quality offspring (larger males may be healthier/live longer/fight disease better, skin pattern reflects diet/health)
      - handicap hypothesis
        
        why would peahens choose a mate with the fattest heaviest tail that'd weigh them down ?
        
        only genetically superior mates can survive with such a handicap
      - sensory exploitation
        
        evolution in males of a signal that exploits the tendency of females to be attracted to certain stimuli (ex. males become red b/c females are good at detecting red objects)
    - - morphological differences between sexes (i.e. males bigger than females for dominance)
    - - increase likelihood that a male's sperm with fertilize the female's eggs even if she's mated with multiple males
      - ex. sperm transfer organs ???
- - - - rare phenotypes are favored (fitness has a negative relationship with phenotype frequency)
      - can make rare alleles more common, maintaining variation
      - can occur as a result of predators forming a "search image" for more common phenotypes
      - can result from resource competition (genotypes differ in resources so rarer genotype has fewer competitors)
      - rare genotypes should become increasingly common --> selective advantage decreases correspondingly
    - - favors common forms and therefore eliminates variation
      - the rare a genotype becomes, the greater the chance it will be selected again
  - - - favors individuals with copies of both alleles, and thus helps retain both alleles in the population
      - ex. sickle cell anemia
- - - - allele for one gene may have multiple different effects depending on alleles present at other genes
      - interaction between alleles of different genes affects a single trait