Week 5 Flashcards
(14 cards)
How do you determine whether a population is in Hardy-Weinberg equilibrium, even though it is rare to see in nature.
5
HWE is established after one generation of random mating. Following establishment of HWE, genotype and allele frequencies remain unchanged from generation to generation.
The Hardy-Weinberg principle only holds under a number of assumptions:
(1) Random mating
(2) Population is infinitely large (or can be treated as such)
(3) Population is closed
(4) No mutations
(5) No selection
Why do we study Hardy-Weinberg equilibrium, even though it is rare to see in nature?
Hardy-Weinberg Equilibrium is an ideal state that provides a baseline against which scientists measure gene evolution in a given population.
How does a population evolve (experience a change in allele frequency in the absence of selection)?
Genetic drift:
This is evolution simply due to random chance or random changes in the allele frequencies due to sampling error
Describe the relationship between population size and genetic drift.
All populations are finite in size and, therefore, genetic drift occurs to come degree in all populations. This violates the second HWE assumption.
Explain what happens to heterozygosity as the frequency of an allele approaches 1.
Heterozygosity declines as the frequency of one allele approaches 1
Define effective population size (Ne) and name the factors that can influence Ne
Effective population size is the number of individuals in an ideal population (in which all adults produce equal number of gametes) that produces the rate of genetic drift seen in the real population.
Influences on effective population size:
(1) male reproductive skew
(2) variation in number of progeny
(3) sex ratio
(4) natural selection
(5) cross-generational inbreeding
(6) fluctuations in population size (especially during founder effects)
Describe the neutral theory of molecular evolution.
A small minority of mutations are advantageous and fixed by natural selection. Many mutations are disadvantageous and eliminated by natural selection.
The vast majority of mutations that are fixed are effectively neutral and fixed by genetic drift.
Holds that mutations occur at a relatively constant rate, termed the molecular clock.
Neutral mutation rates are expected to be highest in non-functional DNA (pseudogenes) and higher in third-base positions than second-base positions in codons.
- Motoo Kimura
Explain the relationship between mutation rate, population size, and allele fixation
Provide evidence for neutral theory of molecular evolution.
- missed this slide *
Calculate an inbreeding coefficient
Inbreeding coefficient (F)– probability that a random pair of gene copies, inherited by offspring from two parents, is identical by descent.
F= (proportion of F1 generation with the autozygous allele) x (proportion of F2 generation with the autozygous allele)
- double check this info when recording is posted
Define autozygous and allozygous
Autozygous means identical by decent
Allozygous means two different alleles from two different origins
This is regarding inbreeding.
Parent gives an allele to both siblings, when they mate together the offspring has two of the same allele from the same origin.
Understand what happens to heterozygosity under inbreeding.
Heterozygosity under inbreeding greatly decreases.
What are the bottle-neck and founder effects?
A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due to environmental events.
the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population (think few butterflies migrate to an island and start a new population).
Do the practice question in the slides
