B - Genetics, populations, evolution and ecosystems

• Abiotic factor is a non-living, physical condition in an ecosystem such as temperature, light, soil conditions and pH.
• Adaptation is an increase in an individual's chances of survival and reproduction through altering or adjusting structure or habits, often occurring through natural selection.
• Allele is a different version of a gene.
• Allele frequency is how often an allele occurs in a population.
• Autosomal-linkage is when two or more genes with loci on the same autosome (i.e. not a sex chromosome) are linked.
• Biotic factors are the effects of activities of living organisms on other organisms such as food availability, predation and competition.
• Carrying capacity is the maximum number in a population that can be sustainably supported in an ecosystem.
• Climax community is a fairly stable, final community at the end of succession.
• If two genes are closer together on an autosome, they are more likely to be split during chromosomal crossover.
• During meiosis, genes are not separated by independent segregation.
• Scientists believe that these species evolved from two species found on mainland USA.
• The Caribbean species could have evolved through geographical isolation, separate gene pools, no interbreeding, gene flow (between populations), variation due to mutation, different selection pressures, differential reproductive success, and change in allele frequency.
• Scientists may use percentage cover rather than frequency to record the abundance of a particular species present.
• On islands in the Caribbean, there are almost 150 species of lizards belonging to the genus Anolis.
• Abiotic factors that can affect an organism's environment include temperature, light intensity, availability of water, mineral content, pH, water-holding and drainage capacities of soil.
• In a diploid organism, the alleles at a specific locus may be homozygous or heterozygous, for example, in a sister chromatid pair, one chromatid has H allele, other has h allele.
• In mammals, females have two X chromosomes (XX), while males have one X and one Y (XY).
• Codominant alleles are alleles that are both expressed in the phenotype, i.e. neither is recessive.
• Ecological niche is the role of a species within its habitat, governed by adaptation to both abiotic and biotic conditions.
• Epistasis is when the allele of one gene masks the expression of another gene in the phenotype.
• Evolution is the change in allele frequencies (in a population) over time.
• Gene is a sequence of bases on a DNA molecule located on chromosomes that instruct protein synthesis.
• Types of variation: Discontinuous (result of genetic factors), Continuous (result of environmental factors)
• What the Hardy-Weinberg principle predicts: Frequencies of alleles in a population don't change from one generation to the next
• Factors causing variation in population size: Effect of abiotic factors, Interactions between organisms
• Assumptions made when using the mark-release-recapture method: No significant population changes due to immigration/emigration, Marking hasn't affected survival chances, Marked animals have mixed with the population, No significant population changes due to deaths/births
• Economic consequences of the spread of a major pest species: Cost of control/removal, Cost of restoring habitat/conservation, Loss of income from tourism/recreation
• Reasons for conserving woodlands: Protecting habitats/niches, Protecting endangered species, Reducing greenhouse effect, Source of medicines/chemicals/wood, Reducing erosion/eutrophication
• Definition of allopatric speciation: Geographical isolation due to physical barriers
• The mark-release-recapture method can be used for estimating population size by capturing a large sample of organisms, marking them, releasing them back into the habitat, and then capturing a second sample and counting the total number caught and the total number marked
• Ways in which new species may arise: Isolation (geographically or reproductively), Genetic variation, Natural selection, Time
• Natural selection arises from variation in individuals of the same species and selection pressures such as predation, disease, and competition, resulting in differential survival and reproductive success
• Other sources of genetic variation: Random fertilisation of gametes, Fusion of gametes is a matter of chance and independent of each other
• Sex-linked: Gene with loci on a sex chromosome (X or Y)
• Species occupying different ecological niches have an advantage because they can utilize different resources and reduce competition within the same habitat
• Conditions for the Hardy-Weinberg principle: Organisms are diploid and reproduce sexually, Alleles are not sex-linked, No emigration or immigration, No mutations, No natural selection, Large population, Random mating
• Primary succession: Pioneer species adapted to hostile abiotic conditions colonize the environment, make conditions less hostile, new species outcompetes pioneer species, biodiversity and complexity of ecosystem increase until climax community is reached
• Types of succession: Primary succession, Secondary succession
• Population: All the organisms of one species in a particular habitat (at the same time)
• Definition of genetic bottleneck: Large reduction in population size leading to reduced genetic diversity