Selection Flashcards
Natural Selection
Phenotypic variation occurring on a trait due to survival and reproduction of particular traits
What are the four forms of selection?
Directional selection
Disruptive selection
Stabilizing selection
Frequency-dependent selection
Is heritability negative or positive for phenotypes under selection?
Positive
What is directional selection?
Selection occurring in a single directions altering the mean but not changing the variance
What is disruptive selection?
No change in the mean
Increases the variance
What is stabalizing selection?
No change in mean, decrease in variance
Frequency dependent selection?
Survival of one trait depends on who you are around
Negative frequency dependent selection:
If the trait is rare it does really well creating a super dynamic system
Positive frequency dependent selection:
The more common the trait is, the better it does (eventually becomes fixed)
How does gene flow effect natural selection?
NEED TO ASK FRANCO
How does genetic drift effect natural selection?
if you have a small population, genetic drift has large effect and causes alleles to go to fixation so no selection is occuring
what does (s) represent?
the selection coefficient
What does evolution depend on?
The size of the population relative to the selection coefficient
In what case does selection overcome drift?
s>1/4Ne
How are advantageous alleles lost?
Due to drift if small population because drift is random! This is also how deleterious alleles can become fixed
Does adaptation happen through mutations of large or small effect?
Small effect
Fishers model
Displays why it is easier to get adaptations of small effect mutations because the path to “the best trait” is more controlled
What does a selective sweep do to variation?
reduce genetic variation near the locus under selection
What is a selective sweep?
reduction or elimination of variation among the nucleotides in neighboring DNA of a mutation as the result of recent and strong positive natural selection.
Candidate Genes
those loci hypothesized to be under selection.
MC1R: melanocortin-1 receptor
The gene that controls skin color. Evolved 1.2 million years ago
UVA
Degrades folate
Neural tube disorders
Spermatogenesis
Skin cancer
UVB
Cholesterol -> vitamin D Calcium absorption Immune function Reduces inflammation Modulation of cell growth
What form of selection is controlling melanin?
Directional? Cholesterol -> vitamin D Calcium absorption Immune function Reduces inflammation Modulation of cell growth
How many genes affect skin pigmentation?
six
Meme
an element of a culture that may be passed from one individual to another by nongenetic means, especially imitation.
Cultural evolution determine by:
Transmission errors (mutation) Statistical effects in small populations (drift) Differential transmission of variants depending upon their utility (selection) Transmission of variants between populations (migration)
Dual Inheritance System
The phenotype is determined by genetic and cultural traits
These inheritance systems interact to influence the transmission of genes and memes
Niche Construction
Cultural evolution alters the environment
Natural selection favors genetic mutations that facilitate the adoption of adaptive cultural practices
Cultural evolution may also constrain genetic evolution, and vice versa
Neolithic Transition
Farming produces 10-100 times more human-consumable calories per acre than hunter-gathering
Salivary amylase gene (AMY1) CNV
Lactose Persistence
Prior to the domestication of animals, only mothers provided milk
Lactase is not expressed in adults in other primates and varies among human populations.
Lactase persistence has been proposed to have evolved in response to selection generated by the advent of dairying practices during the Neolithic transition.
Which came first – lactase persistence (LP) or dairying?
Dairy but only populations with LP can dairy
Lactase
Enzyme expressed in small intestine
Breaks down lactose into glucose & galactose
