87 Starter What is speciation The evolution of new species from existing species Learning Objectives Define speciation Describe geographical isolation Explain how geographical isolation can lead to the formation of new species ID: 320309
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Slide1
Speciation
8.7Slide2
Starter
What is speciation?
The evolution of new species from existing species.Slide3
Learning Objectives
Define speciation
Describe geographical isolation
Explain how geographical isolation can lead to the formation of new speciesSlide4
Speciation - Species
What is the definition of a species?
A group of individuals that share similar genes and can breed together to produce fertile offspring.
Each species will have a number of populations
Usually, individuals will breed with individuals in the same population Slide5
How could 2 populations become different species?
Over time they become so different that they can no longer interbreed
Therefore they stop interbreeding
Allele frequencies will change in the different populations
Selection pressures will be different in different areas
Populations become separated
Write out these into the correct order of what would happen to cause speciation.Slide6
How could 2 populations become different species?
Populations become separated
Therefore they stop interbreeding
Selection pressures will be different in different areas
Allele frequencies will change in the different populations
Over time they become so different that they can no longer interbreedSlide7
Population of individuals
= individual organismSlide8
(2)
Population become geographically separateSlide9
(3) Physical barriers stop interbreeding between populations. = MountainSlide10
(3) Populations adapt to new environments.Slide11
(3) Differences accumulate in the gene pool leading to development of new species.Slide12
Examination questions
1) What is
stabilising
selection ?
2) What is directional selection?
3) What is speciation?
4) The following table shows the results of an investigation into hair length in golden hamsters in a climate where the temperature is decreasing. Hair length is controlled by a single gene with two alleles. H represents the allele for short hair, which is dominant over the allele for long hair, represented by h.
a) Describe the relationship between the frequency of the recessive long hair allele and temperature. Suggest an explanation for this relationship. (4 marks)
b) What type of selection is responsible for this change in allele frequency? (1 mark)
Average temperature/ °C
Frequency of h allele
22
0.11
210.13190.19180.20160.23Slide13
Answers
Selection that tends to eliminate the extremes of the phenotype range within a population. Arises when environmental conditions are stable.
Selection that operates towards one extreme in a range of variation.
The evolution of two or more species from existing species.Slide14
Answers
4a) As temperature decreases from 22°C to 16°C the frequency of h, the long hair allele, increases from 0.11 to 0.23 (1 mark)
This could be because the allele for long hair is more beneficial at colder temperatures (1 mark).
Hamsters with the h allele will have a greater chance of surviving and passing on their genes, including the beneficial h allele (1 mark)
A greater proportion of the next generation will inherit the beneficial allele and the frequency of the h allele will increase (1 mark).
4b) Directional selection (1 mark)Slide15
Hangman
Pick a genetic key word, once it has been guessed you must give the definition of the word