Population genetics Flashcards
1
Q
Define population genetics
A
- The study of allele and genotype frequency distribution and change
2
Q
Which evolutionary processes influence population genetics?
A
- Natural selection
- Genetic drift
- Mutation
- Gene flow
3
Q
Define a locus
A
- A specific position of a specific chromosome where a particular gene or genetic marker is located
4
Q
Define an allele
A
- An alternative form of gene or DNA marker that is located at a specific locus (a variation of the same sequence of nucleotides at the same place on a DNA molecule)
5
Q
Define a genotype and a phenotype
A
- Genotype: the genetic make-up of an individual at a specific gene or DNA marker (the genetic makeup of an organism - it describes an organism’s complete set of genes)
- Phenotype: observable, physical characteristics due to genetic make-up
6
Q
State three types of genotype
A
- Homozygote: Possess the same alleles at a specific locus
- Heterozygote: Possess different alleles at a specific locus
- Polymorphism: Multiple forms (alleles) of a gene in a population
7
Q
Outline the Hardy-Weinberg principle
A
- The conclusion that if a population is in genetic equilibrium, then:
- The frequencies of the alleles will not change from one generation to the next
- That genotype frequencies can be predicted from allele frequencies
- A simple formula to predict this for Mendelian loci
8
Q
Expand the Hardy-Weinberg equation
A
- Alleles are represented by p and q: (p + q) = 1 - where p and q are proportions of each allele
- p is the dominant allele frequency
- q is the recessive allele frequency
- Genotype frequency prediction for offspring = (p + q)2 = 1
- Thus, p2 + 2pq + q2 = 1
9
Q
How would you use the HW formula?
A
- As we cannot know the exact figures for genome frequency (p2, 2pq and q2), we use HW to estimate the numbers
- Only if we have allele frequency data for the necessary population
10
Q
Outline the conditions for HW equilibrium
A
A population will only be in genetic equilibrium if:
- The population is infinitely large
- Random mating occurs
- No migration
- No natural selection
- No mutation
11
Q
Outline polymorphism
A
- The presence of two or more variant forms of a specific DNA sequence that can occur among different individuals or populations
- The most common type of polymorphism involves variation at a single nucleotide
- Generally not disease causing
- An example of discontinuous genetic variation (such as blood types)
12
Q
What is allele frequency?
A
- The proportion of chromosomes that contain a specific allele (the relative frequency of an allele at a particular locus in a population)
- Different alleles at a locus can be determined by sequencing
- Expressed as a fraction or percentage
13
Q
What does it mean to be autosomal recessive?
A
- It is a** pattern of inheritance characteristic** of some genetic disorders
- “Autosomal” means that the gene in question is located on one of the numbered (non-sex) chromosomes
- “Recessive” means that two copies of the mutated gene (one from each parent) are required to cause the disorder
14
Q
How would you use the HW equation to estimate an autosomal recessive disease?
A
- The frequency of the disease causing allele (q) is derived from the incidence (I) of the disease in the population (often the disease incidence is known, and you must calculate allele and genotype frequencies)
- This relationship allows the estimation of the allelic and carrier frequencies in autosomal recessive (AR) disorders
15
Q
What does it mean to be autosomal dominant?
A
- It is a pattern of inheritance characteristic of some genetic disorders
- “Autosomal” means that the gene in question is located on one of the numbered, or non-sex, chromosomes
- “Dominant” means that a single copy of the mutated gene (from one parent) is enough to cause the disorder
