speciation - unit 4 AOS 2

Question 1

speciation

Answer 1

• speciation is the process where population genetically diverge until they become different species.
• Populations of the same species living under different environmental conditions are likely to be subject to different selection pressures. This leads to natural selection, and the allele frequencies in their gene pools change, as different alleles are retained due to being advantageous.
• Over many generations, under different selection pressures, these populations can
  become increasingly different from each other in structure, physiology and behaviour.
  Eventually they can become so different that they form two distinct species.

Question 2

what are species

Answer 2

For sexually reproducing organisms, species are recognised as different when they are not able to interbreed under natural conditions, or, if they interbreed, the offspring are either inviable or, if they survive, are sterile (not fertile).

Question 3

isolating mechanisms

Answer 3

In order for speciation to occur, populations need to be separated and isolated in some way that prevents gene flow or interbreeding.

Question 4

pre-reproductive isolating mechanisms

Answer 4

geographical - a barrier such as mountain range may prevent species from breeding

temporal - the species may have different breeding times

behavioural - mating behaviour may differ

structural - physical differences can make mating difficult

Question 5

post reproductive mechanisms

Answer 5

gamete mortality - sperm may be unable to penetrate the ovum for fertilisation

zygote mortality - fertilisation may occur but the zygote does not survive

hybrid sterility - a viable offspring may be formed byt it will not be fertile.

Question 6

allopatric speciation

Answer 6

• Allopatric speciation occurs when a geographical barrier physically isolates the populations of an ancestral species, preventing gene flow
• Over many generations, the isolated populations are subjected to different environmental selection pressures, making them subject to natural selection or genetic drift.
• they will evolve in different directions and eventually reach a point of genetic divergence where they become different species and can no longer breed (speciation)

Question 7

sympatric speciation

Answer 7

• Sympatric speciation occurs when a population becomes reproductively isolated without being physically separated
• The reproductive isolation can be caused by temporal or behavioural factors, or caused by chromosomal abnormalities
• Over many generations, species living within the same population can be subject to different selection pressures.
• over time, they will genetically diverge and become two different species.

Question 7

Galapagos finches

Answer 7

• An example of allopatric speciation can be seen in the variety of beak types seen in the finches of the Galapagos Islands
• It has been hypothesised that the formation of these different species of Galápagos finches has largely been a result of allopatric speciation.
• different food sources on each island caused divergence in the beak shape
• This is because each of the islands is separated by the ocean, preventing gene flow.

Question 8

Howea palms

Answer 8

• An example of sympatric speciation can be seen in the different species of Howea palms on Lord Howe Island
• Evidence indicates that variations in soil preference have altered the two palms’ flowering time so that they flower at different times of the year.
• Different flowering times create the pre-zygotic mechanism of temporal isolation.
• This temporal isolation between the two populations of palms caused them to evolve along different pathways
• Over time, the gradual accumulation of genetic differences caused the populations of Howea palms to form separate species