population genetics - lecture 14 Flashcards
what is a locus?
The position in the genome being considered
what are alleles?
alternative DNA sequences
what are SNPs?
Single Nucleotide polymorphisms
How do we get phenotypic difference?
Genes with different alleles that lead to different phenotypes produce genetically- based phenotypic variation
How to determine the alleles frequency?
Frequency of A = number of A alleles/ Total number of alleles
What is the definition of evolution?
change in allele frequencies over Time
What are genotypic frequencies?
Number of individuals with the genotype divided by total number of individuals
How to calculate the genotype frequencies for (AA)?
f(AA)= nAA/N
5 assumptions of the hardy- Weinberg model
- population is very large
- Random mating
- No migration
- no selection
- No mutation
The method behind the Hardy - Weinberg model
Two alleles in a diploid individual are randomly and independently sampled from an infinitely large pool of games
Predicted Genotype frequencies for the Hardy- Weinberg model
Freq. homozygous A (AA)= p^2
Freq. homozygous a (aa)= q^2
Freq. heterozygote (Aa)= 2pq
what are the 2 Hardy - Weinberg model predications
1 - Allelic frequencies of a population do not change due to random mating
2- Genotypic frequencies are the product of allele frequencies ,and will be at these frequencies after a single generation of random mating
How may categories of non random mating are there? which disrupt the H-W assumption
- positive assortative mating = similar individuals tend to mate with each other
- Negative assortative mating= different individuals tend to mate with each other
- inbreeding = individuals tend to mate with relatives
what happens when inbreeding occurs?
- offspring produced by inbreeding are more likely to have two alleles that are identical by descent
- These individuals are homozygous, so inbreeding increases homozygosity and reduces heterozygosity
How is the proportion of inbreeding measured?
inbreeding coefficient F = probability that two alleles are identical by descent
What does F stand for?
proportional reduction in the frequency of heterozygotes compared to that expected in the H-W model
What is the inbreeding depression?
Heterozygosity can be advantageous , but inbreeding reduces the percentage of it.
Therefore, inbreeding can lead to reduced fitness
How can allele frequencies change?
- Genetic drift
- Natural section
- Migration
What is genetic drift?
Random changes in allele frequencies
why does genetic drift occur?
In a finite population, the composition of a selected allele frequency will often deviate from that of the parental gene pool
what is the expected amount of error due to genetic drift?
1/2N
What is a population bottleneck?
When populations go through drastic reductions in population size, it can produce huge ‘ drift events’
what is the founder effect ?
when a new population is founded by very few individuals , the allele frequencies can be very different from the original population
What is fitness?
The average contribution to the next generation made by an individual or genotype
what is overdominance?
Heterozygote has highest fitness. selection maintains both alleles in the population
What is migration?
Movement of alleles from one population to another
what are the advantages of migration?
- Prevents populations form becoming genetically different
- increases the genetic variation within populations
