Evolution may lead to speciation

Question 1

Genetic diversity

Answer 1

• refers to the total number of different alleles in a population

Question 2

Population

Answer 2

• refers to a group of organisms of the same species occupying a particular place at a particular time - than can potentially interbreed.

Question 3

Species

Answer 3

• refers to a group of organisms that can interbreed to produce fertile offspring. They consist of one or more populations

Question 4

What can lead to natural selection?

Answer 4

• greater genetic diversity of a species

Question 5

What can was to greater genetic diversity of a species?

Answer 5

• greater number of different alleles within a species

Question 6

Why does greater genetic diversity of a species lead to natural selection?

Answer 6

• as high probability an individual possesses a characteristic suited to an environmental change

Question 7

Why did numbers of dark moths increase between 1848 and 1895?

Answer 7

1. Large genetic diversity (gene pool) of moths
2. Mutations occurred to make a darker moth
3. This created variation, and gave the darker moths an advantage who could camouflage better than lighter moths from the birds which ate them - they could compete for resources better and adapt better
4. Pale moths were eaten, and the dark moths survived and thrived. (survival of the fittest)
5. Dark moths reproduced and passed on its’ advantageous alleles (i.e., the mutation) to its offspring. Allele frequency for dark moth colour increases (allele for pale decreases)
6. Over time, more light moths died, and eventually 98% of moths became dark coloured; evolution had occurred.

Question 8

How does antibiotic resistance occur?

Answer 8

• by random mutation, some bacteria have an allele for resistance;
• use of antibiotics is the selection pressure: non-resistant bacteria die;
• resistant bacteria more likely to survive to reproduce and pass on their alleles;
• frequency of the resistance allele increases in the bacterial population;
• frequency of antibiotic resistance increases in the bacterial population;

Question 9

What is antibiotic resistance an example of?

Answer 9

• directional selection

Question 10

What is an antibiotic?

Answer 10

• chemical that kills, or inhibits the growth of, bacteria

Question 11

Suggest why antibiotic resistance often spreads in hospitals.

Answer 11

• More antibiotic use in hospitals (greater selection pressure);
• Patients often have weakened immune systems, so bacteria divide faster.

Question 12

Variation

Answer 12

• differences between individuals of the same species and of different species

Question 13

Sources of variation:

Answer 13

• Random mutation
• meiosis
• random mating in population
• random fertilisation of gametes

Question 14

Why does random mutation result in variation?

Answer 14

• can result in new alleles of a gene. Many mutations are harmful but, in certain environments, the new allele of a gene might bring a benefit that increases reproductive success

Question 15

Why does meiosis result in variation?

Answer 15

• crossing over of homologous chromosomes and independent segregation of homologous chromosomes) produces genetic variation.

Question 16

Genetic diversity

Answer 16

• the number of different alleles of genes in a population

Question 17

What is the difference between phenotypic variation and genetic variation?

Answer 17

• phenotypic variation is caused by both genetic and environmental factors

Question 18

What is continuous variation?

Answer 18

• Range of phenotypes between two extremes
• No distinct categories
• Tends to be quantitative
• Controlled by many genes
• Strongly influenced by the environment

Question 19

What is discontinuous (discrete) variation?

Answer 19

• Limited number of phenotypes with no intermediate values
• Data is in distinct categories
• Tends to be qualitative
• Controlled by a few genes (usually one)
• Unaffected by environment

Question 20

Genetic drift

Answer 20

• describes random changes in allele frequencies within a population
• Genetic drift can happen in any population but is only significant in small, geographically separated populations where variant/mutant alleles become progressively more common in the offspring

Question 21

population/genetic bottleneck

Answer 21

• a sharp reduction in the size of a population due to environmental events (e.g. earthquakes, floods, disease, or droughts) or human activities (such as genocide)

Question 22

Founder effect

Answer 22

• Reduced genetic diversity which results when a population is descended from a small number of colonizing ancestors. Allelic frequency is more representative of these original ‘founders’.

Question 23

In extreme cases, what can genetic drift lead to?

Answer 23

• Reduction in genetic variation
• Reduce the ability of the population to survive in a new environment
• May contribute to the extinction of a population or species
• Could lead to the production of a new species

Question 24

Speciation

Answer 24

• the separate evolution of two populations of the same species, to form two separate species

Question 25

Step 1 of forming new species

Answer 25

1. Isolation: Typically, a geographical barrier of some kind separates a population, restricting members from interbreeding

Question 26

Step 2 of forming new species

Answer 26

2. genetic variation: Restricted populations become genetically different from one another, particularly when mutations occur. Gene pools of both populations diversify

Question 27

Step 3 of forming new species

Answer 27

3. Natural selection: will lead to changes in the allele frequency of each population. The different phenotypes each combination of alleles produces will be subject to selection pressure, meaning each population is required to adapt to their local environments. This is called adaptive radiation – there are further changes in the allele frequency and the populations evolve

Question 28

Step 4 of forming new species

Answer 28

4. Speciation: two sub populations can no longer interbreed, creating two new, but closely related species, each with their own gene pool. They have become reproductively separated / isolated

Question 29

What are the two forms of speciation?

Answer 29

1. Allopatric speciation
2. Sympatric speciation

Question 30

Allopatric speciation

Answer 30

• refers to the form of speciation where two populations of the same species become geographically isolated

Question 31

Sympatric speciation

Answer 31

• refers to the form of speciation where new species form from the same original population in the same habitat; there is no geographical isolation

Question 32

Allopatric speciation

Answer 32

• Two populations of the same species end
  up in different habitats that are geographically isolated from each other;
• causes reproductive isolation since the two populations are physically separated - there is no gene flow between populations / gene pools
  remain separate;
• There’s different selection pressures in different habitats (biotic/abiotic factors)
• Mutations cause differences (refer to question) that lead to further reproductive isolation
• Different alleles are selected for and passed on in each population, leading to a change in the
  frequency of the alleles;
• Eventually the different populations cannot interbreed to produce fertile offspring; they have become two different species;

Question 33

Lord Howe Island in the Tasman Sea possesses two species of palm tree which have arisen via sympatric speciation. The two species diverged from each other after the island was formed 6.5 million years ago. The flowering times of the two species are different. Using this information, suggest how these two species of palm tree arose by sympatric speciation

Answer 33

• Occurs in the same habitat / are not geographically isolated;
• Mutations cause different flowering times; Reproductive separation / isolation, OR No gene flow OR gene pools remain separate;
• Different allele/s passed on OR Change in frequency of allele/s;
• Disruptive (natural) selection;
• Eventually different species cannot (inter)breed to produce fertile offspring;

Question 34

There are 9 subspecies of giraffe. These subspecies evolved when populations of giraffe were separated for long time periods. Each subspecies has distinct coloured skin markings. Some biologists have suggested that up to 6 of these subspecies should be classified as different species.
(a) Explain how different subspecies of giraffe may have evolved from a common ancestor. Use information from the passage in your answer.

Answer 34

• No interbreeding / geographic(al) isolation / reproductive isolation;
• Mutation linked to (different) markings/colours;
• selection/survival linked to markings/colours;
• adapted organisms breed;
• change/increase in allele frequency/ies;

Question 35

There are 9 subspecies of giraffe. These subspecies evolved when populations of giraffe were separated for long time periods. Each subspecies has distinct coloured skin markings. Some biologists have suggested that up to 6 of these subspecies should be classified as different species. Biologists compared mitochondrial DNA of the different subspecies of giraffe. They concluded that 6 of the 9 subspecies are separate species. Suggest how they came to this conclusion.

Answer 35

• (Compare DNA) base sequence / base pairing / (DNA) hybridisation;
• different in six (species) / similar in three (subspecies)

Question 36

Sympatric speciation

Answer 36

• Occurs in a population all in the same habitat with no geographical isolation (in different niches of that habitat);
• Mutations cause differences (refer to question) that lead to further reproductive isolation
• Different alleles are selected for and passed on in each population, leading to a change in the
  frequency of the alleles;
• Eventually the different populations cannot interbreed to produce fertile offspring; they have become two different species;