Population genetics Flashcards
What is a species?
A species is a group of individuals of common ancestry which closely resemble each other and are capable of interbreeding to produce fertile offspring. They will have similar morphological, physiological, biochemical and behavioural features. They will be reproductively isolated from other species.
Does “p” represent?
Frequency of a dominant allele in a population.
What does “q” represent?
The frequency of the recessive allele in a population.
What is the equation for allele frequencies?
p + q = 1
What is the Hardy Weinberg equation?
p^2 + q^2 + 2pq = 1
What does the Hardy Weinberg principal predict?
The Hardy Weinberg principal predicts that the gene pool in a population will not change from one generation to the next.
{This means allele frequencies remain constant over time, the population is said to be in Hardy Weinberg equilibrium.}
What conditions are needed to apply the Hardy Weinberg equation?
- The population is a large one
- There is random mating (no individual has a selective advantage)
- There is no mutation (no new alleles are introduced)
- There is no migration.
What are the sources of genetic variation in a population?
- Mutation
•Gene mutation- introduces new alleles into the population.
• Chromosome mutation- occurs when chromosomes fail to separate during meiosis, so that extra (or occasionally fewer) chromosomes appear in the affected individual.  - Meiosis
Produces a variety of genetically different haploid cells through segregation of alleles, independent assortment of chromosomes and crossing over. - Sexual reproduction
• particularly where cross-fertilisation is ensured, is the most important means of promoting genetic variability in populations.
• it involves the joining of genetic material from the haploid cells from two genetically different individuals.
•meiosis and sexual reproduction act to shuffle combinations.
How is genetic variability maintained?
By diploidy.
Diploidy shelters rare recessive alleles because heterozygotes are important reservoirs of genetic variation in populations
If heterozygotes have a selective advantage they would increase in number but would always interbreed to produce homozygotes.
What is polymorphism?
Polymorphism is the presence of two or more distinct forms in a population.
How is Polymorphism maintained in a population?
- Predation
Predators tend to hunt the most common form (easier to see) until it becomes the least common form. Then, another form becomes the favoured prey allowing others to increase in the population. - Heterozygotes
If heterozygous was selected (more likely to survive), then while heterozygotes increase in frequency, they would always interbreed to produce more homozygotes.
What is natural selection?
Natural selection is the process by which individuals that are better adapted to their environment survive and breed, while those less well adapted fail to do so. The better adapted organisms are more likely to pass on their characteristics (alleles) to succeeding generations. Therefore, the frequency of the allele that gives the selective advantage will increase in the population.
What is evolution?
The change in genetic composition of the population.
Explain stabilising selection.
Occurs where environmental conditions are largely unchanging.
It favours the model or intermediate forms and acts against extremes.
Stabilising selection does not lead to evolution.
Stabilising selection maintains the adaptive norm.
It reduces variation in phenotype.
[Graph gets narrower]
Explain directional selection.
Occurs with changing environmental conditions.
The majority of an existing form may no longer be best suited to the environment.
Some extreme forms may have a selective advantage in the changed conditions. They will contribute more offspring, and the alleles these offspring possess, to the next generation.
The result is a change in the genetic composition of the population (evolution).
