Speciation topic - 1. Natural selection to polyploidy

Mutation

A permanent change in the base sequence of DNA to produce new alleles

Natural Selection

Living things adapting to a change in the environment. Living things with alleles that allow for adaptation to the selection pressures will survive and reproduce successfully. Living things without these alleles will not reproduce successfully.

Meiosis

Cell division whereby gametes are produced. It leads to genetic variation through independent assortment, crossing over/recombination and segregation.

Genetic drift

A change in the allele frequency of a population as a result of chance events rather than natural selection.

founder effect

change in allele frequencies as a result of the migration of a small subgroup of a population from the original population.

bottleneck effect

A change in allele frequency following a dramatic reduction in the size of a population. Usually as a result of a natural disaster.

Stabilising selection

a type of natural selection in which genetic diversity decreases as the population stabilises on a particular trait value - mean of the range often selected for.

directional selection

Natural selection in which individuals at one end of the phenotypic range survive or reproduce more successfully than do other individuals.

disruptive selection

natural selection in which individuals at the upper and lower ends of the curve have higher survival (fitness) than individuals near the middle of the curve for a particular trait.

Species

A group of similar organisms that can breed and produce fertile offspring.

Speciation

Process by which a species give rise to one or more new species

Allopatric speciation

The formation of new species in populations that are geographically isolated from one another.

Geographical barriers

formed by canyons, mountain ranges; bodies of water, deserts, and other features organisms can't cross

Reproductive isolation

Separation of species or populations so that they cannot interbreed and produce fertile offspring

Sympatric speciation

The formation of new species in populations that live in the same geographic area.

Pre-Zygotic isolation

mating and fertilization are prevented (no zygote formed)

Temporal isolation
(TIME - seasonal)

Gene flow prevented due to species having different times of day to mate, or month, year, seasons

Ethological isolation
(Behavioural)

Species don't recognise courtship, mating behaviour, so not attracted.

Structural isolation
(mechanical)

Animals sexual organs not shaped to 'fit' and prevents mating. Flowers in plants determine which organism can act as pollinator

Gamete incompatibility

Something that stops zygote forming. Sperm not attracted to egg (biochemical differences)

Post-zygotic isolation

Isolating mechanisms after zygote formed.

Hybrid

Living thing formed from sperm and egg fusing of a different species.

Hybrid inviability
(Non-viability)

Embryo produced from different species fertilisation usually dies

Hybrid sterility

Hybrid offspring that survive usually STERILE, so can't produce gametes to reproduce themselves.

Hybrid breakdown

Hybrid survives, is able to produce viable gametes, but offspring they produce have serious genetic problems. Reduces their fitness and ability to reproduce etc.

Polyploidy

To have 3 or more sets of chromosomes (3n or 4n). Can happen if something goes wrong in meiosis in gametes. This leads to instant speciation.

If full chromosome sets in gametes join together a tetraploid is made (4n). This will be able to grow, but could reproduce asexually. More common in plants that animals.

Autopolyploidy/
autoploidy
('auto' means 'self')

Polyploidy happens within same species due to non-disjunction. Hybrid may be sterile (3n) or fertile (4n, 6n)

Allopolyploidy
('allo' means 'others')

Mating between 2 different, but closely related species. Hybrid maybe sterile (3n), but fertile hybrid maybe produced later on.

Tetraploid

Cell contains 4 more than normal haploid number of chromosomes. Tetraploid are fertile.

Non- disjunction

During MEIOSIS, spindles cause wrong number of chromosomes to be pulled to poles. Gamete have more/less than normal number of chromosomes.