What are mutations
non-repaired alterations in the nucleic acid sequence of a genome
Relevance of mutations
- fuel of evolution
- silent mutations occur at a steady rate
- # of accumulated mutations is proportional to the time they’ve been accumulating for
What is genetic drift?
stochastic changes in allele freq due to sampling variation b/w generations
Significance of genetic drift (5)
- only significant in finite populations
- caused by chance events
- causes loss of genetic diversity over time
- inc freq of deleterious alleles
-inversely proportional to population size
what is a stochastic change/ event?
random events that cannot be predicted.
eg random survivors of a tornado will change the population’s allele freq due to chance
Sampling with replacement
taking a random sample from a generation, forming the new gen
significance of sampling with replacement
- you can determine the state of new populations by sampling previous generations with replacement
- cannot get diversity of original population back when a trait is lost due to random sampling
effects of genetic drift on a small population
- as pop’n gets smaller, sampling with replacement has a more exaggerated effect
- in very small populations, alleles get fixed faster
when an allele has no adaptive advantage, what forces are in effect?
only genetic drift (allele freq can change by chance), selection does not play a role as there is not selective advantage of the allele
effect of genetic drift on freq and variance of an allele
freq: stays stable over time (around 0.5)
variance: increases each generation
What is identity by descent?
probability that 2 alleles chosen at random come from the same ancestral allele in the prior generation
what happens to rate of loss of heterozygosity depending on population size?
rate of loss of H increases as population size decreases. Larger populations maintain H for longer
what is effective population size?
size of a population under HWE that transfers the same amount of H as the actual population
ie the randomly mating individuals
what is the census population?
the total individuals in a population
Causes of reduced heterozygosity (genetic drift)
(7) IABUUFP
1) inbreeding
2) assortative (non-random) mating
3) breeding systems
4) unequal sex ratios
5) unequal # of offspring
6) fluctuations in population size
7) population bottlenecks and founder events
what is inbreeding + significance
mating between relatives
increases probability of identity by descent -> increases homozygosity
how does inbreeding affect fitness?
severe inbreeding can cause physical, emotional and intellectual disabilities -> decreases fitness
what are fluctuations in population size?
a periodical change in population size that can be due to disease, hunting habits, weather etc
what is a population bottle neck?
an event causes a huge drop in population. Further gens are produced based on this small population
what is a founder event?
a small group leaves the population to start a new one somewhere else.
define natural selection
differential reproductive success of genotypes
what does differential reproductive success mean?
how advantageous a trait is
two types of natural selection
Directional and balancing selection
describe directional selection (3+ what are the types)
- selecting for or against a phenotype
- decreases genetic diversity
- 2 types:
- positive selection
- negative selection
