Speciation 8.7

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

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

How could 2 populations become different species? Write out these into the correct order of what would happen to cause speciation. 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

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 interbreed

Population of individuals = individual organism

(2) Population become geographically separate

(3) Physical barriers stop interbreeding between populations (3) Physical barriers stop interbreeding between populations. = Mountain

(3) Populations adapt to new environments.

(3) Differences accumulate in the gene pool leading to development of new species.

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 21 0.13 19 0.19 18 0.20 16 0.23

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.

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)

Hangman Pick a genetic key word, once it has been guessed you must give the definition of the word