Lecture 7 Flashcards
Random Genetic Drift
Changes in allele frequencies caused by the random sampling of genes
Scientist that worked on random genetic drift
Sewell Wright
4 features of genetic drift
- Unbiased
- Loss of genetic diversity
- Causes populations to become more different
- All gene copies trace back to single ancestor (MCRA)
Name an experimental example of random genetic drift
Drophilia populations some became fixed for mutations others lost it after many generations
What is a gene tree?
A way to show the ancestries of copies of a gene
Gene tree examples in humans
- Mitochondrial MRCA (eve), 150 kya
- Y chromosome MRCA (adam), 200 kya
Difference in DNA sequence are a result of ______
Mutations of the gene tree
Describe the relationship between genetic drift and population size
Inverse, as populations increase genetic drift decreases, as populations decrease genetic drift increases
What is N(c)
Effective population size
What is an effective population size?
The size of an idealized (constant) population that would have the same amount of drift as the population of interest
Relationship between effective population size and genetic drift
1/N(c)
What size would a population need to be, to not experience genetic drift?
infinitely large
What is a population bottleneck
Entire population is reduced in size and a new population is formed by few individuals
Consequences of a population bottleneck
Loss of genetic diversity and rare alleles become more common
What are 3 examples of a population bottleneck?
- elephant seals nearly hunted to extinction have low genetic diversity
- Native human populations far from Africa have low genetic diversity compared to within Africa
- Polydactyly rare allele in Amish became prevalent
Can selection and genetic drift act at the same time?
Yes
When can drift be ignored?
When the strength of selection is far larger than 1/N(c)
What is inbreeding load?
The fixation of deleterious mutations by drift in small populations
What is a wild example of genetic drift?
- Small population of vipers was declining but reversed by introduction of snakes from another population
- Wooly mammoths last days on island
