Evolutionary Processes Flashcards
locus
A location where a gene can occur
allele
A particular version of a gene
- Complex organisms usually have two alleles at each locus
heterozygous
An organism with different alleles at a particular locus
homozygous
An organism with two copies of the same allele at a particular locus
genotype
collection of an individual’s genes
phenotype
collection of an individual’s physiological and physical traits
Dominant vs Recessive
If individuals with genotype XY have the same phenotype (on average) as those with XX, we say that X is a dominant allele and Y is a recessive allele
incompletely dominant
If XY individuals have an intermediate phenotype (between XX and YY), we say X and Y are incompletely dominant.
Hardy-Weinberg equilibrium assumptions
- Random mating within a closed population
- No differences in fitness between genotypes
- No mutation
- No drift
null model
tells us what to expect if complicating effects are absent
Directional selection
moves a population in a particular direction
ex: giraffe necks
Multi-directional selection
Directional selection can change through time with the environment
ex: finch beaks get thicker when food scarce and smaller when food abundant
Stabilizing selection
tends to keep the population where it is
- begins as directional, then meets target and stabilizes
ex: human birthweights
Disruptive selection
favors phenotypes different from the average value
ex: animals that get eaten a lot may want to look different from peers
- may lead to speciation
speciation
the formation of new species
Balancing selection
tends to maintain allele diversity
Heterozygote advantage
when heterozygotes have higher fitness
Frequency dependence
when rare types have higher fitness
Genetic drift
change in allele frequencies due to random sampling
- Some individuals have more offspring than others due to chance events
- Offspring receive certain parental alleles, and not others
Founder effects
occur when a new population is started by a small number of individuals
Bottlenecks
occur when a population becomes small, then large again
lost
An allele may drift to a frequency of 0
- disadvantageous alleles are often lost
fixed
An allele may drift to a frequency of 1
- Advantageous alleles are usually fixed
Gene flow
movement of alleles from one population to another
Mutations
heritable errors in copying DNA
Sex
- does not directly change allele frequencies
- not a source of new alleles but it is a source of new combinations
Inbreeding
mating between close relatives
- commom in smaller pop
- more homozygous loci
- usually leads to decrease fitness
Sexual selection
Occurs when there is heritable variation in traits related to success in obtaining mates
Sexual dimorphism
trait differences between males and females
Investment in reproduction
Who invests more? Results?
females invest much more in each offspring than males do
- If females invest a lot in each offspring, they can maximize fitness by being choosy
about mates
- If males invest little in each offspring, they can maximize fitness by mating as much as possible
Variation in reproductive success
Who has higher VRS and the effects of such?
Males often have greater variation in reproductive success than females do
(means that winning contests is more impor- tant to male fitness)
- Side-effect of the fact that females usually invest a lot in each offspring:
– Reduces potential total number of offspring – Makes females desirable to males
