Introduction à la Génétique des Populations

Study Notes

Introduction to Population Genetics

Population genetics studies the distribution and changes in allele and genotype frequencies within populations.
It aims to understand the factors that maintain or alter allele and genotype frequencies across generations.

Hardy-Weinberg Equilibrium (HW)

In a large population, where matings are random (panmixia), there's no migration or selection, and mutation rates are constant, genotype frequencies remain stable over generations.
This equilibrium is described by the equation p² + 2pq + q² = 1
- p represents the frequency of allele A.
- q represents the frequency of allele a.
- p² is the frequency of homozygous genotype AA.
- 2pq is the frequency of heterozygous genotype Aa.
- q² is the frequency of homozygous genotype aa.

Applications of Hardy-Weinberg Equilibrium

Studying species evolution and migration.
Genetic Medicine:
- Knowing an allele's frequency in a population allows calculating genotype frequencies for AA, Aa, and aa.
- Knowing a disease's prevalence lets estimate allele and genotype frequencies of the related gene.

Deviation from Hardy-Weinberg Equilibrium

Factors that affect the equilibrium:
- Inbreeding (consanguinity): Increases the frequency of homozygous genotypes.
- Mutation hotspots: Specific regions in the genome where mutations occur more frequently.
- Natural Selection: Favors or disfavors certain genotypes.
- Migration: Influences allele and genotype frequencies through gene flow.
- Genetic drift: Random fluctuations in allele frequencies, particularly in small populations.

Inbreeding (Consanguinity)

Inbreeding is defined as mating between genetically related individuals.
Inbreeding coefficient (F):
- Chance of an inbred individual inheriting two identical copies of a gene from a common ancestor.

Mutations Hotspots

Areas in the genome where mutations occur more frequently than the average across the genome.
Examples: Neurofibromatosis type 1 (NF1) and Duchenne muscular dystrophy.

Natural Selection

Genotypes' viability and fertility are impacted by environmental and genetic factors.
Selection against dominant or X-linked traits: Affected individuals often don't transmit their mutated allele due to low viability or infertility.
In some cases, heterozygotes have an advantage against certain environments, and may have higher reproductive success.

Migration

Movement of individuals between populations leads to changes in allele frequencies.
Small population migrations lead to greater changes.
Founder effect: Migration of a small population to a new region carries a limited gene pool, which leads to significant changes in allele frequencies in the new population.

Genetic Drift

Random changes in allele frequencies over generations, significant in small populations.
Loss or fixation of allele can occur in small populations.

Effect of Founder

Higher frequency of specific alleles in a population, stemming from a small group of individuals.

Description

Ce quiz explore les principes de base de la génétique des populations, y compris l'équilibre de Hardy-Weinberg. Vous apprendrez comment les fréquences alléliques et génotypiques se stabilisent dans des populations de grande taille. Découvrez l'importance de ces concepts dans l'évolution des espèces et la médecine génétique.