P2 Speciation and Individual Variation

Question 1

How does speciation occur?

Answer 1

• For speciation to occur, there must first be reproductive isolation.
• This can be a result of geographical separation or variations caused by random mutations, eg. creating differences in courtship behaviour or flowering seasons.
• As a result the two new populations have separate gene pools.
• Within each new population, there is genetic variation caused by random mutations. As a result of natural selection, different alleles are selected for and passed on, changing allele frequencies in each population, until the two populations become so different that they cannot interbreed to produce fertile offspring, becoming two different species.

Question 2

What is allopatric speciation?

Answer 2

When speciation arises from geographical separation - two new species located in different habitats.

Question 3

What is sympatric speciation?

Answer 3

When speciation arises from fertilisation or courtship behaviour - two new species are located in the same habitat.

Question 4

What are the two types of natural selection?

Answer 4

1. Stabilising selection - favours intermediate phenotypes. Eg. human babies with an intermediate weight are more likely to survive, reproduce and pass on the allele for intermediate birth weight, shifting the allele frequency in favour of this allele over many generations.
2. Directional selection - favours the extreme of the phenotype. Eg. bacteria with antibiotic resistance are more likely to survive, reproduce and pass on their allele for resistance, meaning over many generations allele frequency shifts towards this extreme.

Question 5

What is genetic drift?

Answer 5

• The process by which allele frequencies change due to chance.
• Genetic drift has the largest impact in small populations, because there is a higher risk of certain alleles reducing to a very low number, or being wiped out completely.

Question 6

What are the two types of genetic drift?

Answer 6

1. Genetic bottleneck: occurs when the size of a population dramatically decreases eg. due to an event like a forest fire.
2. The Founder effect: when individuals in a large population break away and form a new population.

Question 7

What is artificial selection?

Answer 7

When farmers or breeders selectively breed plants or animals with desirable characteristics.

Question 8

What are the steps of artificial selection of animals/plants?

Answer 8

1. Males and females are selected with the desired characteristic.
2. The males and females with the desired characteristic are interbred.
3. From the offspring produced, farmers select males and females that also have the desired characteristic and interbreed them.
4. This process is repeated for several generations.

Question 9

What problems can artificial selection cause?

Answer 9

1. Selecting only desired characteristics reduces the gene pool and genetic variation of a population.
2. It can make selected for individuals more vulnerable to diseases.

• To make these problems less severe, farmers can interbred with a wild variety (phenotype found in individuals in the wild).
• Since they are the same species, wild variety and crop variety can still interbreed.
• This makes wild varieties a resource of genetic material (new alleles) increasing gene pool and genetic variation, meaning the population is able to better adapt to environmental change.

Question 10

How can artificial selection create ethical issues?

Answer 10

When animals, eg. dogs are selectively bred for aesthetic reasons, it can cause health issues for the animal.