10.3 Gene pools and speciation

Question 1

What is a gene pool?

Answer 1

All of the genes and their different alleles, present in an interbreeding population

Question 2

What does a large and small gene pool indicate?

Answer 2

Large: high amounts of genetic diversity, increasing the chances of biological fitness and survival, more genetic variation

Small: low amounts of genetic diversity, reducing biological fitness and increasing chances of extinction, more likely to inherit mutations

Question 3

What is genetic equilibrium?

Answer 3

When all members of a population have an equal chance of contributing to the gene pool
* individuals that reproduce contribute to the gene pool of the next generation

Question 4

What are 4 ways evolution can occur?

Answer 4

• Mutations - random changes to the structure of DNA introducing new alleles
• Selection pressures favouring the reporoduction of some varieties over others
• Gene flow (movement of alleles between population) emerging between different populations
• Genetic drift - changes in gene pool due to a chance/random event e.g. trampling/hunting

Question 4

What is the impact of random events on a small population?

Answer 4

A significant effect

Question 5

What does evolution require of in populations to do over time?

Answer 5

Evolution requires that allele frquencies change with time in populations
* Gene pools can be used to determine allele frquency - the proportion of a particular allele within a population

Question 6

What does evolution require of in populations to do over time?

Answer 6

Evolution requires that allele frquencies change with time in populations
* Gene pools can be used to determine allele frquency - the proportion of a particular allele within a population

Question 7

What are the 3 main types/patterns of natural selection?

Answer 7

• Stabilising
• Directional
• Disruptive

Question 8

What happens in stabilizing selection?

Answer 8

• Selection pressures act to remove extreme varieties
• Bell shape graph - normal distribution
• Natural selection that favours the average/intermediate phenotypes (positive selection) and extreme phenotypes are selected against (negative selection) and may be removed from gene pool all together
• Reducing genetic variation
• Occurs when the environment is stable

Question 9

What happens in disruptive selection?

Answer 9

• Selection pressures act to remove intermediate varieties, favouring the extremes
• Opposite extreme traits are favoured, average trait is eliminated
• Extreme phenotypes are favoured (positive selectional) and average/intermediate phenotype is selected against (negative selection)
• Relatively rare
• Occurs when there are fluctuations in the environmental conditions e.g. seasons

Question 10

What happens in directional selection?

Answer 10

• the population changes as one extreme of a range of variation is better adapted
• Natural selection where an environmental change gradually favours a new phenotype (e.g. peppered moths)
• Occurs when there is a gradual change in the environment

Question 11

What is speciation?

Answer 11

The formation of a new species by the splitting of an existing population

Question 12

What are two main types of isolating mechanisms that can cause speciation?

Answer 12

1. Geographical separation aka allopatric speciation
2. Reproductive aka sympatric speciation

Question 13

What is allopatric speciation?

Answer 13

The formation of two diferent species from one original species, due to geographical isolation
* populations are separated by geographical features such as lackes, rivers, oceans and mountains
* There is a barrier to gene flow between the populations
* The isolated populations are subjected to different selection pressures in two different environments so undergo independent changes to the allele frequencies within their gene pools as a reult of mutation, selection and genetic drift

Question 14

What is sympatric speciation?

Answer 14

The formation of two different species from one original species, due to reproductive isolation, while the population inhabit the same geographical location
* More common in plants than in animals
* Can be due to genetic changes e.g. change in chromosome number or mutation
-> Changes in flower structure
-> Changes in courtship behaviour

Question 15

What are two types of sympatric isolation?

Answer 15

Temporal and behavioural

Question 16

What is temporal sympatric isolation?

Answer 16

Populations may mate or flower at different seasons or different tymes of the day

Question 17

What is behavioural sympatric isolation?

Answer 17

When closely related individuals differ in their courtship behaviour, they are often only successful in attracting members of their own population

Question 18

Do populations have the same allele frequencies?

Answer 18

Different populations have different allele frequencies

Question 19

What are the two theories about the pace of evolutionary change?

Answer 19

• Gradualism
• Punctuated equilibrium

Question 20

What is gradualism?

Answer 20

It is the idea that species slowly change through a series of intermediate forms

Gradualism predicted that evolution occured by a long sequence of continuous intermediate forms. The absence of these intermediate forms was explained as imperfections in the fossil record

Question 21

What was gradualism confronted by? What was explained about it?

Answer 21

It was confronted by gaps in the fossil record i.e. an absence of intermediate forms
The absence of these intermediate forms was explained as imperfections in the fossil record

Question 22

What is punctuated equilibrium?

Answer 22

The idea that long periods of relative stability in a species are punctuated by periods of rapid evolution

Question 23

According to the theory of punctuated equilibrium, what do the gaps in the fossil record show?

Answer 23

• It might not be gaps at all, as there was no long sequence of intermediate forms
• Events such as geographic isolation (allopatric speciation) and the opening of new niches within a shared geographic range can lead to rapid speciation
• Rapid change is much more common in organisms with short generation times like prokaryotes and insects

Question 24

What is polyploidy?

Answer 24

• When an organism has more than two sets of homologous chromosomes
• A common source of reproductive speciation
• Has more chromosomes than they should have
• Occur more commonly in plants, though it does also occur in less complex animals

Question 25

What can polyploidy result from?

Answer 25

Hybridisation events between different species

Question 26

How can polyploids who’s chromosomes originate from the same ancestral species occur?

Answer 26

• When chromosomes duplicate in preparation for meiosis but then meiosis doesn’t occur. The result is a diploid gamete that when fused with a haploid gamete produces a fertile offspring.
• In other words, the polyploid has now become reproductively isolated from the original population

Question 27

What can polyploid plant mate with?

Answer 27

It can self pollinate or it can mate with other polyploid plants

Question 28

What speciation can polyploid lead to?

Answer 28

Sympatric speciation

Question 29

What are does the Allium genus include?

Answer 29

Onions, leeks, garlic and chives

Question 30

How do Allium reproduce?

Answer 30

Asexually

Question 31

How might polyploidy help?

Answer 31

• May confer an advantage over diploidy under certain selection pressures
• Can be used for human benefit e.g. agriculture, food production