Midterm Questions Flashcards
What role have chromosome variations played in evolution (3)
- Duplications = new functions emerge/ loss of function
- Inversions = reduce recombination
- Polyploidy = speciation
What is differential selection
Different phenotypes have different relative fitness as they are subject to different selection pressures
Stronger selection pressure will change allele frequencies more quickly
Often see a cline/gradient across environments
How does selection for a rare allele, influence the allele frequency over time
If rare allele is dominant then evolution by selection is fast
If the rare allele is recessive then evolution by selection is slow
How do selection and mutation work together
Mutations create new alleles which can be beneficial, deleterious, or neutral
Selection acts on beneficial and deleterious alleles, allowing them to either increase or decrease in frequency
Deleterious alleles remain due to the mutation-selection balance, mutations produce more
Explain and give an example of the homogenizing effect of gene flow
Gene flow mixes alleles from different populations together making the populations more similar to each other
(Ex. Bladder campion example)
How does gene flow increase genetic variation in a population
Allows new alleles to move into the population
How does drift decrease genetic variation
As we lose alleles in the population, the genetic variation decreases. Drift causes alleles to be fixed or lost (and if one allele is fixed, any others are lost)
Why does heterozygosity decrease with drift
Drift causes one allele to go to fixation while any others are lost. If there is only a single allele, there can be no heterozygotes. Even if more than one allele remain, the loss of an allele reduces how many options there are to make heterozygotes
why do we need variation
Variation is required for natural selection (it is what natural selection acts upon)
It allows for different adaptations to occur
How do we quantify variation
Heterozygosity, number of alleles, % polymorphism, and haplotype diversity
What maintains variation in a population
Mutation, recombination, gene flow, and hybridization
What are some problems with phenotype vs. Genotype
Genotype and phenotype are not always equivalent
A phenotype may not reflect genotype (phenotypic plasticity, environmental affects, maternal effects, or genomic imprinting)
A genotypic difference may not necessarily be a phenotypic difference (ex. Heterozygotes in a regular dominance relationship)
Describes two types of natural selection
Sexual selection = kind of natural selection which mating preferences influence the traits of the organisms (ex. Deer with large antlers)
Ecological selection = natural selection that operates on a species inherited traits without referring to mating or secondary sex characteristics (ex. Mice in sand)
