Final - Population Genetics Flashcards
Population genetics
- the study of the distribution of genes in populations and how the frequencies of genes and genotypes are maintained or changed from generation to generation
Population
- local group of organisms belonging to a single species
- composed of interbreeding individuals who share a common gene pool
Gene Pool
- the set of genes contained in an entire population
Allele frequency
- frequency of an allele in a population, as measured by its percentage of the total number of alleles at a particular gene locus
Genotype frequency
- percentage of individuals in a population who are homozygous or heterozygous for an allele at a particular locus
Hardy Weinberg Law
- can be used to determine allele and gentotype frequencies in a population.
- states these frequencies remain constant from one generation to the next under 5 conditions
5 conditions of Hardy Weinberg Law
- Large population size
- Random mating between individuals in the population
- No mutations in the alleles
- No migration into or out of the population
- No natural selection (i.e. all genotypes are equally viable and fertile)
Equation for Allele Frequency
p + q = 1
A) (a
Equation for genotype frequency
p^2 + 2pq + q^2 = 1
(AA) (Aa) (aa)
Equation for Frequency of Allele from genotype Frequency
Freq (allele) = Freq (homozygote) + 1/2 Freq (heterozygote)
B = BB + 1/2 Bb
p = p^2 + 1/2 pq
Frequency of phenotype => genotype => allele
p = Sqrt (p^2)
a aa
Recessive allele Frequency in males
= phenotype frequency, since males have only 1 X chromosome
Applications of Population genetics
- Use in genetic Counseling
- To plan genetic screening programs
- In molecular diagnostics testing
Consanguineous Mating
- interbreeding
- 2 individuals who share a common ancestor preceeding 2 or 3 generations
Assortive Mating
- based on factors like race, ethnic groups, culture differences, religious beliefs, intelligence, language
Inbred
- children from the result of consanguineous mating
Founder effect
- occurs when a population is formed by a small group of individual
- alleles carried by these “founder” are established in the new population
- ex: discovery of new island
Population bottleneck
- change in gene frequency that occurs when a population is suddenly reduced in size and then expands again
- ex: natural disaster = volcano
Genetic drift
- random changes in allele frequencies from generation to generation in small population
- caused by founder effect and population bottleneck
Fitness
- a measure of the relative survival and reproductive success of a specific individual or genotype
Race
- a subdivision of species that has come to differ in the frequencies of alleles it possesses
Factors leading to Change in Gene Frequencies
- Small population size
- subject to genetic drift
- race - Non- random mating
- assortive mating
- consanguineous mating - Natural Selection
- fitness - Mutation
- Migration - rapid introduction of new alleles
Heritability
- the degree to which a trait is inherited
- expressed as the proportion of variability caused by genetic differences
- ranges from H = 0 - 1.0
H = 1.0
- genetic differences = 100% of variation
- Environmental factors = contribute to 0%
H = 0
- Environmental factors = 100% of the variation
- genetic differences = contribute to 0%
Genetic variance
- phenotypic variability in a population due to differences in genotypes
Environmental variance
- phenotypic variability in a population due to differences in environmental factors
How monozygotic twins are used to determine heritability
Monozygotic= genetically identical = 100%
Dizygotic = share 50% of their genes
- if environmental factors play more of a role, the concordance value will be less than 100% in monozygotic twins and lower than 50% in dizygotic twins
Mutation and Polymorphism
- mutation rate = 1 mutation per 100,000 - 1 million copies of a gene
- 1 in 10 people is likely to have received a new mutation
- mutations established in > 1% of the population are known as polymorphisms
Multifactorial Traits
- traits that result from genetic variance (2 or more genes) and environmental variance (1 or more factors)
- exhibit continuous variation, in varying degrees along a continuum
- ex: height, weight, skin color, intelligence, diabetes mellitus, manic depression
