Topic 4 Flashcards
What is an overview of genetics?
gene = combination of two alleles
one allele per chromosome
usually one chromosome from each parent
What is genetic variation?
diversity of alleles in a population
often measured by determining proportion of heterozygotes or number of alleles at various locations
What is phenotype variation?
variety in visible expression of “types”
can be “types” (male/female) or continuous
What is statistical variation?
measure of difference from central tendency
What is evolution?
change in the frequencies in a population (gene pool) between generations
What are the five factors that cause evolution?
- Natural Selection
- Sexual Selection
- Mutations
- Gene Flow
- Genetic Drift
How does sexual selection cause evolution?
non-random mating: increases or decreases the probability that a specific individual will mate
due to preferred phenotypes, inbreeding, etc.
may decrease genetic variation
How do mutations cause evolution?
a change in an individual’s DNA
can be caused by error in DNA replication or by structural damage to DNA (radiation)
mutations are random (environment does not cause the “right” mutations to arise)
a mutation can be “good”, “bad” or neutral in the current situation
How does gene flow cause evolution?
transfer of genes (alleles) between populations
examples: interbreeding, migration
increased variation within a population
decreased variation between populations
How does genetic drift cause evolution?
changes in allele frequency due to chance (regardless of natural selection)
allele frequencies “drift” from one generation to the next
the impact of drift is greater in small populations
examples: bottleneck and founder effect
What is the founder effect?
new population established by a few colonizers
small fraction of the total genetic variation compared to the ancestral population and change in allele frequency (evolution)
What is the bottleneck effect?
only a few individuals survive
only these few reproduce in the next generation
gene frequency in the next generation is different than previous generation
rare alleles are more likely to be lost due to drift
What are the three mechanisms of natural selection?
- Directional Selection
- Disruptive Selection
- Stabilizing Selection
What is directional selection?
extreme phenotype is favored (highest fitness)
response to steady change in the environment
frequency distribution of alleles shifts
can cause loss of allelic varieties
loss of genetic variation
directional shift in the mean of the population (variance stays the same)
statistical/phenotype variance may stay the same
What is disruptive selection?
extremes are favored
results in polymorphism (2 or more divergent phenotypes)
maintains genetic variation
