Microevolution
Changes in allele frequencies in a population
Not creating a new species
Speciation
The process by which one species splits into 2 or more species
Genetic basis of evolution
Evolution occurs in populations
Some variation due to environment and some due to heredity
The change of the frequency of genes within a population over several generations.
Hardy Weinberg principle & equations
Principle: Allele and genotype frequencies do not changes, population at genetic equilibrium
What are mutations?
A change in an organism’s DNA.
New alleles can arise by mutation
Sexual recombination
Which genes from each parent will combine
Net change is minimal from generation to generation; mostly reshuffling
Natural selection
Differential success in reproduction
Major factor altering allele frequencies
Genetic drift
Random evolutionary changes in a population
Decrease genetic variation within a population
Increase genetic differences among different populations
Sexual Selection
Natural selection for mating success, not necessarily advantageous in environment
HW equations
Equation for allele frequency: p+q=1
P= dominant Q= recessive
Equation for genotype frequency:
p^2+2pq+q^2=1
P^2= homozygous dominant
2PQ= heterozygous
Q^2= homozygous recessive
How do mutations cause genetic variation?
Mutations in gametes can introduce new alleles that can be passed down to offspring. Change from generation is very small. Mutation rates are low in animals and plants, higher in prokaryotes.
Bottleneck effect
Number of individuals is drastically reduced by a disaster
Some alleles overrepresented and others underrepresented or even eliminated.
Founder effect
A few individuals become isolated from a larger population, bring with them only a small fraction of the genetic variability
Gene flow
Migration of breeding individuals between populations
May cause a population to lose alleles (decreased genetic variability) and other to gain some (increased genetic variability)
Types of selection
Directional selection: Favors individuals at one end of the phenotypic range
Disruptive selection: Favors individuals at both extremes of the phenotypic range
Stabilizing selection: Favors intermediate variants (acts against extreme phenotypes)
Intrasexual selection:
Direct competition among individuals of ONE sex for mates of the opposite sex
Intersexual selection
Occurs when individuals of one sex (usually females) are choosy in selecting their mates from individuals of the other sex
Asexual reproduction pros and cons
Pros: more efficient (less time,resources, energy)
Cons: No genetic differences = risk of total wipeout
Sexual reproduction pros and cons
Pros: Genetic differences that may aid in disease resistance
Cons: inefficient ( energy, time, resources)
