7. Genetics, Populations, Evolution & Ecosystems: Key Terms

• Abiotic factors**:** Non-living components of an ecosystem, such as temperature, light intensity, moisture, soil pH, and oxygen levels.
• Adaptation**:** A characteristic of an organism that improves its chances of survival in its environment.
• Allele**:** A specific version of a gene.
• Allele frequency**:** The proportion of a particular allele within a population's gene pool.
• Allopatric speciation**:** Speciation that occurs when two populations are geographically isolated, preventing interbreeding.

• Autosomal linkage**:** The occurrence of two or more genes on the same autosome, making them more likely to be inherited together due to reduced crossing over during meiosis.
• Autosome**:** A chromosome that is not a sex chromosome (X or Y).
• Belt transect**:** A method for studying the distribution of organisms along a line, using quadrats placed at intervals to measure abundance and diversity.
• Biodiversity**:** The variety of species, genes, and habitats within a given area.
• Biotic factors**:** Living elements of an ecosystem, including food availability, pathogens, and predators.
• Carrying capacity**:** The maximum population size that an ecosystem can support over a prolonged period, determined by biotic and abiotic factors.

• Chi-squared test**:** A statistical method used to assess whether observed inheritance patterns are significant.
• Climax community**:** The final, stable community of organisms established at the end of ecological succession.
• Codominant**:** A condition where both alleles in a heterozygous individual equally influence the phenotype.
• Community**:** The combined populations of different species living in the same habitat and interacting with each other.

• Conservation**:** The active management of ecosystems and biodiversity to preserve natural resources, often involving succession control.
• Degrees of freedom ($χ²$ test)****: The number of categories in a dataset minus one.
• Dihybrid inheritance**:** The inheritance of two different genes, located on separate chromosomes, determining two distinct traits.
• Diploid**:** Refers to a cell containing two complete sets of chromosomes, one from each parent.
• Directional selection**:** A type of natural selection favouring individuals with one extreme phenotype, shifting population traits in a specific direction.
• Disruptive selection**:** A form of selection favouring individuals with extreme phenotypes, reducing the prevalence of intermediate forms.
• Dominant**:** An allele that is always expressed in the phenotype, represented by a capital letter.
• Ecosystem**:** A dynamic system comprising biotic (living) and abiotic (non-living) components and their interactions in a specific area.
• Epistasis**:** A relationship where the expression of one gene is influenced by another gene.
• Evolution**:** The gradual change in allele frequencies in a population over time due to mechanisms like natural selection.
• Gene**:** A section of DNA coding for a polypeptide or functional RNA.
• Gene pool**:** The total collection of different alleles present in a population.
• Genetic drift**:** Random changes in allele frequencies, particularly significant in small populations.
• Genetic variation**:** Differences in genetic makeup within a population, caused by mutations, meiosis, or random fertilisation.
• Genotype**:** The genetic makeup of an organism, describing its alleles.
• Habitat**:** The specific environment where an organism lives.
• Hardy-Weinberg principle**:** A model predicting allele frequencies in a population will remain constant if conditions such as no mutations, no natural selection, no migration, large population size, and random mating are met. The equation is:

$$p^2 + 2pq + q^2 = 1.0$$

where is the dominant allele frequency, and is the recessive allele frequency.

• Heterozygous**:** Having two different alleles for a particular gene (e.g., Ff).
• Homozygous**:** Having two identical alleles for a gene (e.g., ff).
• Interspecific competition**:** Competition between members of different species.
• Intraspecific competition**:** Competition between members of the same species.
• Locus**:** The specific position of a gene on a chromosome.
• Mark-release-recapture**:** A method for estimating population sizes of mobile species by marking, releasing, and recapturing individuals. Population size is estimated using:

$$\text{Population size} = \frac{\text{(Number marked in 1st sample) × (Number caught in 2nd sample)}}{\text{Number of marked individuals recaptured}}$$

• Monohybrid inheritance**:** The inheritance of a single gene.
• Multiple alleles**:** When a gene has more than two possible alleles.
• Natural selection**:** The process by which beneficial alleles increase in frequency in a population due to environmental pressures, first described by Charles Darwin.
• Niche**:** The role and position of an organism within its ecosystem, including its interactions with other species and the environment.
• Phenotype**:** The observable characteristics of an organism, resulting from the interaction between its genotype and environment.
• Pioneer species**:** The first species to colonise bare or hostile environments, such as lichens on bare rock.
• Population**:** All individuals of the same species living in a specific area at the same time.
• Predator**:** An organism that hunts and consumes other organisms.
• Prey**:** An organism that is consumed by predators.
• Quadrat**:** A square frame used in ecological sampling to measure organism abundance and distribution. It may be a point quadrat or a frame quadrat.
• Random sampling**:** A technique to avoid bias in sampling by using random coordinates or locations.
• Recessive**:** An allele expressed only in the absence of a dominant allele, represented by a lowercase letter.
• Selection pressures**:** Environmental factors, such as predation or competition, that influence the survival and reproduction of organisms, driving natural selection.
• Sex-linkage**:** A gene located on a sex chromosome ($X$ or $Y$), affecting inheritance patterns.
• Speciation**:** The formation of new species due to the evolution of reproductively isolated populations. Types include allopatric and sympatric speciation.
• Species**:** A group of similar organisms capable of interbreeding to produce fertile offspring.
• Stabilising selection**:** A type of selection favouring intermediate phenotypes and selecting against extremes, maintaining population traits.
• Succession**:** The gradual change in a community of organisms in a particular area over time.
• Sustainable**:** The ability to maintain resources or conditions for future generations.
• Sympatric speciation**:** Speciation occurring within the same geographic area due to reproductive isolation.
• Systematic sampling**:** A sampling method using regular intervals (e.g., along a belt transect) to measure organism abundance and distribution in an area of gradual change.
• Variation**:** Differences among individuals due to genetic factors, environmental factors, or a combination of both.