Bio 3.5 ,, Modes

Reproductive isolating mechanism (RIM)

A barrier that prevents two organisms from differing species from mating and producing fertile offspring / prevents successful interbreeding / prevents gene flow.

Prezygotic RIM

Reproduction is prevented before fertilisation therefor preventing gene flow.

Postzygotic isolating mechanisms

Mechanisms that prevent the formation of fertile offspring, therefore preventing gene flow.

Examples of RIMS

Geographical isolation, behavioural or territorial isolation, temporal

The niche

The role of the organism within the environment.

Species

A species is a group of members in a population that can interbreed to produce fertile viable offspring.

Speciation

Is creation of a new species/ divergence of species from a common ancestor /that is reproductively isolated or due to gene flow being prevented.

Gene flow

When individuals move between populations, and this allows new mutations /new combinations of alleles to move into each population; thus the species does not diverge.

Cline

The continual increase or decrease in some characteristics between neighbouring populations. Which can be related to the change in biotic and abiotic factors in a given range.

Endemic species

Those found in one location and nowhere else.

Allopatric Speciation

When populations become geographically isolated, each are subjected to different selective pressures and reach a point where they are reproductively isolated and no interbreeding can occur if they were to come across each other.

Sympatric speciation

The formation of new species from a common ancestor in the same geographical area due to difference is in niche or behaviour.

Sympatric species

Species, which previously diverged from a common ancestor, and now exist in the same area but remain reproductively isolated.

Selection pressures

Are factors that affect fitness / reproductive success and include limits on resources(food, habitat, space, and mates) and the existence of threats (predators, disease, climate change).

Natural selection

Individuals with better adapted phenotypes / characteristics are more likely to survive and reproduce. Or Variation of alleles / phenotypes exists in populations.

Individuals

With better adapted phenotypes will have increased fitness compared to less suited individuals, so are more likely to reproduce and pass on their favourable alleles which will increase in the population (name a selection pressure for another A point).

Directional selection

Occurs when a phenotype towards one end of the range (extreme phenotype) is favoured over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype (identify example in the question.)

Disruptive selection

Occurs in a population when two or more phenotypes have higher fitness than intermediate phenotypes (Identify example in the question).

Stabilising selection

Occurs in a population when intermediate phenotypes have the highest fitness, rather than those at one or both extremes (Identify example in the question).

Genetic diversity

The variation of heritable traits in a population.

Genetic drift

The random fluctuations in the numbers of alleles in a population.

Founder Effect

a new population established by a very small number of individuals from a larger population

A mutation

A permanent alteration in the nucleotide DNA base sequence (of a gene).

Polyploidy

Where an organism has more than two homologous sets of chromosomes in their somatic cells.

Non-Disjunction

When the spindle fibres do not form and homologous chromosomes fail to separate causing more/or less chromosomes to be present in the gamete cells.