AS 91605 - Evolutionary processes leading to speciation

Selection pressure

factors or variables which cause a certain phenotype of an organism to have a better chance of surviving and reproducingin a given environment, influencing evolutionary change.

Natural selection

Natural selection is the process where organisms with traits that help them survive and reproduce are more likely to pass those traits on to the next generation resulting in changes in a population, with beneficial traits becoming more common.

Species

A group of organisms that normally interbreed to produce fertile offspring.

Speciation

The formation of new species through evolutionary processes, often due to genetic divergence and environmental factors.

Evolution

The change in the gene pool (and therefore the inherited characteristics ) of populations over successive generations.

sexual reproduction

Sexual reproduction is the process where organisms combine genetic material from two parents to produce offspring. It requires the production of gametes (sperm and egg) through meiosis, which creates new combinations of alleles. This increases genetic variation from one generation to another, making populations more diverse.

Independant Assortment

The process during meiosis where alleles for different genes line up independently of one another. Each homologous pair will separate independently into the gametes and each gamete will contain a random assortment of chromosomes leading to genetic variation in offspring.

Crossing Over

Occurs when homologous chromosomes line up where the inner chromatids can break off and join the chromatid of the other chromosome. This process transfers alleles from one chromosome to another to create recombinants.

Segregation

The process during meiosis where pairs of alleles are separated when the homologous chromosomes splits so that each gamete receives one allele from each pair leading to all daughter cells being unique.

Mutations

Mutation is a permanent change in the base sequence of DNAthat can lead to new traits in an organism. These changes can be caused by various factors, including environmental influences or errors during DNA replication.

Allele frequency

The number of one allele relative to the total number of alleles for that one gene.

Gene Flow

the transfer of genetic material(genes) from one population to another. Occurs in immigration and emigration.

Reasons of change in gene pool

Genetic drift, gene flow, mutation, non-random mating, and natural selection.

Founder effect

When a small number of individuals become geographically isolated from the original population.

Bottleneck effect

In a catastrophe such as natural disaster or human actions, populations may be reduced in number which means that the type of alleles present will decrease as well as the allele frequency.

Stabilising selection

The selection pressure selects the individuals with average traits and selects against the two extremes

Directional selection

When the selection pressure selects one end of the trait, and selects against the other end of the trait where the allele frequency shifts in one direction.

Disruptive selection

The selective pressure favours the two extremes of the trait. Average phenotypes are selected against.

Demes

A local population that has no or limited gene flow with members of other populations of the same species due to geographical or ecological isolation.

Cline

A cline is a gradual change in a trait or genetic characteristic of a species over a geographic area. This variation is usually caused by environmental differences, such as temperature, altitude, or food availability, leading to populations adapting to local conditions.

Ring Species

A special type of cline in which two ends of a cline join to form a loop. Each population can interbreed with nearby populations, but the ones at the two ends of the ring are too different to reproduce with each other.

Speciation and Reproductive isolation

When populations become isolated, the gene flow between these populations stop which leads to mutations and changes in allele frequencies between the populations (due to differing selection pressures). As divergence occurs, the populations become geographically isolated.

What is a reproductive isolating mechanism

any factor that reduces or stops gene flow and stops members from different species from breeding together and producing a fertile offspring.

RIM’s may either be - give examples

Prezygotic that is before fertilization

Postzygotic that is after fertilization

Geographical

were species occupy different areas with no geographical overlap - No geographical overlap means that two species or populations live in completely separate areas and do not share any part of their habitat.

Allopatric speciation

occurs when two populations of the same species become geographically isolated from each other. Natural selection, mutations, genetic drift and founder effect act differently on the two populations, leading to phenotype differences. If the two populations meet and are unable to breed, then it means speciation has occurred.