Speciation

Question 1

Define a species

Answer 1

Organisms that can reproduce to make fertile offspring

Question 2

What are the basics of speciation?

Answer 2

-if 2 populations become separated, the flow of alleles is reduced
-differing environments will lead to differing advantageous genes and the populations will evolve along separate lines
-unable to reproduce successfully if the populations are reintroduced
-separate species each with their own gene pool

Question 3

Explain what allopatric speciation is and the different stages

Answer 3

= Evolution of a new species occurring as a result of a physical barrier e.g geographical barrier
1) the separation of 2 populations of 1 species through a barrier
2) there will be different selection pressures in the two populations, therefore different allele frequencies will occur
3) the 2 populations can’t breed with each other because of the physical barrier, so there is no transfer of alleles between the populations
4) eventually the frequency of alleles in the 2 populations become so different that members of the 2 populations can no longer breed together to form fertile offspring, and so new species are made

Question 4

Explain what sympatric speciation is

Answer 4

-when populations living together become reproductively isolated, either before fertilisation (prezygotic) (isolated by a barrier so gametes never from an embryo) or after mating (postzygotic)

Question 5

What are the 4 different types of isolation in sympatric speciation?

Answer 5

1. Temporal = breeding times slowly separate between 2 populations until can no longer breed with one another as not fertile
2. Behavioural = something changes in behaviour such as a different bird song which attracts new females
3. Mechanical = physically are not able to mate due to size difference etc
4. Gametic = only form of prezygotic isolation in which mating occurs, but is unsuccessful because the gametes are incomptable or not attracted to each other so no zygote is formed

Question 6

What is postzygotic isolation?

Answer 6

When individuals successfully mate and a zygote is formed, but the resulting offspring is unsuccessful e.g hybrid sterility, hybrid inviability or hybrid breakdown

Question 7

Explain what hybrid inviability is

Answer 7

-the hybrid offspring are either weaker then the parent species or totally inviable (can’t stay alive)
-this could be caused by minor or major genetic defects, and results in big decreases in reproduction

Question 8

Explain what hybrid breakdown is

Answer 8

-when we get successful mating with viable, fertile offspring in the first generation, but when the offspring try to have offspring, the second generation can be inviable, infertile or show reduced fitness

Question 9

Explain what hybrid sterility is

Answer 9

Even if the hybrid offspring is otherwise healthy, either one or both sexes is sterile so doesn’t have functional gametes to reproduce