5.19 Understand how allopatric or sympatric speciation occurs

What is gene flow?

where members of a species can pass genes from one member to another

Allopatric speciation

occurs where populations are geographically isolated from one another, preventing the groups from mating with each other, and so the populations have become geographically isolated.

Sympatric speciation

occurs where the two populations become reproductively isolated in the same environment without any geographical barrier, due to other isolating mechanisms.

Explain how two populations, isolated by a mountain range and in different climates, may form into two different species.

-Reproductive isolation most likely due to mountain range

-Prevents a group of individuals from breeding with the rest of the population

-Over time the two groups become different due to selection pressures, and random mutations accumulate

-Eventually, the two groups can no longer breed to produce fertile offspring and they become separate species

When the population is fairly small, there will be random changes in allele frequency, called ____

genetic drift.

genetic drift

changes in allele frequencies in the gene pool of a population which are purely due to chance events and not selection pressures

give 6 ways in which sympatric speciation can occur

ecological isolation, temporal isolation, behavioural isolation, physical incompatibility, hybrid inviability, hybrid sterility

temporal isolation

The species exist in the same area, but reproduce at different times

behavioural isolation

The species exist in the same area, but do not respond to each other's courtship behaviour

What is speciation?

the formation of a new species

Which is the most common method of speciation?

allopatric

What geographical features may isolate populations?

mountain range, river, stretch of ocean

ecological isolation

where the species occupy different parts of the habitat

physical incompatibility

species co-exist but there are physical reasons that prevent them from copulating

hybrid inviability

in some species, hybrids are produced, but they do not survive long enough to breed

hybrid sterility

hybrids survive to reproductive age, but cannot reproduce, e.g. mules

Explain how separation of the Arctic and Irish regions by sea may have contributed to the diversion of polar bears and Irish brown bears into 2 separate species (3)

-different conditions in each region

-therefore different selection pressures in each area

-restricted gene flow between separated populations and they are reproductively isolated

Explain how genetic mutation may have contributed to the diversion of polar bears and Irish brown bears into 2 separate species (4)

-gene mutation results in different alleles in the gene pool of one population

-therefore leading to different phenotypes in that population compared to the other

-if the allele is advantageous it will be passed on to offspring

-resulting in genetically unique population that can no longer interbreed with the other population to produce fertile offspring