Topic 7 - Genetics, Populations, Evolution and Ecosystems Flashcards
Define genotype and phenotype.
Genotype: The genetic constitution of an organism (its alleles).
Phenotype: The expression of the genotype and its interaction with the environment
What are alleles?
Different versions of the same gene.
A gene can have multiple alleles (e.g., blood group alleles: IA, IB, IO).
Define dominant alleles
Alleles expressed in the phenotype even with one copy.
Define recessive alleles
Alleles only expressed in the phenotype if two copies are present
Define codominant alleles
Both alleles contribute to the phenotype
What do homozygous and heterozygous mean?
Homozygous: Two identical alleles at a locus.
Heterozygous: Two different alleles at a locus
How is a chi-squared (χ²) test used in genetics?
To compare observed phenotypic ratios with expected ratios, testing goodness of fit.
Used when sample size is large, data are frequencies, and categories are mutually exclusive.
Define population
A group of individuals of the same species, living in the same area at the same time, who can interbreed.
What is a gene pool?
The complete set of alleles of all individuals in a population
What does the Hardy–Weinberg principle assume? (5 assumptions)
Allele frequencies in a population remain constant from generation to generation, provided:
No mutation
Random mating
No selection
Large population
No gene flow
State the Hardy–Weinberg equation and define its terms
p² + 2pq + q² = 1
Where:
p = frequency of dominant allele
q = frequency of recessive allele
p² = homozygous dominant genotype
2pq = heterozygous genotype
q² = homozygous recessive genotype
What are the 3 sources of genetic variation?
Mutation (main source)
Meiosis (crossing over & independent assortment)
Random fertilisation
What is natural selection?
Organisms with advantageous alleles are more likely to survive, reproduce, and pass on their alleles.
Over generations, this increases the frequency of beneficial alleles.
Name and describe the three types of selection.
Stabilising: Favours the average phenotype
Directional: Favours one extreme
Disruptive: Favours both extremes
What is genetic drift and when is it significant?
A change in allele frequency due to chance. More significant in small populations as chance events have larger effects.
What is speciation and how does it occur?
Formation of a new species.
Occurs via:
Allopatric speciation: geographic isolation
Sympatric speciation: reproductive isolation within the same area
How does reproductive isolation lead to speciation?
Prevents gene flow between populations, allowing accumulation of genetic differences, eventually leading to inability to interbreed and produce fertile offspring
Define ecosystem and community.
Ecosystem: All living organisms (community) and non-living factors in an area.
Community: All populations of different species in a habitat.
What is a niche?
The role of a species within its habitat, including interactions with biotic and abiotic factors
What determines carrying capacity?
Abiotic factors (e.g., temperature, light)
Biotic interactions (e.g., competition, predation)
Methods for estimating population size?
Quadrats (random or transect-based): for non-motile organisms
Mark-release-recapture: for motile organisms
What does the mark release recapture method assume?
No migration, random mixing, marked individuals have same chance of survival
What is succession?
The process of change in species composition in an ecosystem over time.
Primary succession: Starts from bare rock
Climax community: Stable, final stage
How do organisms change the environment during succession?
By modifying abiotic conditions (e.g., soil formation), making it less hostile and allowing new species to colonise.
