Unit 1.7 Evolution

Question 1

What is evolution?

Answer 1

The changes in organisms over generations as a result of genomic variations.

Question 2

Where do genomic variations arise from within a population?

Answer 2

From random mutations within the population

Question 3

What role do selection pressures play in evolution?

Answer 3

Selection pressures increase the gene frequencies of any new characteristic that is beneficial to the species

Question 4

what is L.U.C.A

Answer 4

The last universal common ancestor, that supposedly all life on earth can be traced back to

Question 5

Explain what is meant by selection?

Answer 5

• Selection: firstly selection occurs this causes the non-random change in the frequencies of some genetic sequences within a population, for instance some genetic sequences’ frequencies increase because they are selected for. Where other genetic sequences’ frequencies decrease as they are selected against.

Question 6

Explain what is meant by natural selection?

Answer 6

• Natural selection: Natural selection can be defined as the non-random increase in the frequency of DNA sequences that increase survival, and reduction in deleterious sequences.

Question 7

What is meant by a quantitative trait?

Answer 7

A measurable phenotype (remember that the phenotype is the physical appearance of an organism as a result of the proteins that are produced by the organism’s genome)

Quantitative traits vary among individuals, over a range, to produce a continuous distribution of phenotypes.

Question 8

Continuous variables are due to _______________

Answer 8

polygenic inheritance

Question 9

What are the types of selection that can occur?

Answer 9

• stabilising selection
• directional selection
• disruptive selection

Question 10

What happens in stabilising selection?

Answer 10

The average phenotype is selected for, and extreme phenotypes are selected against. This type of selection occurs in an unchanging environment.

As a result the average phenotype remains stabilised and genetic diversity in the population decreases

Question 11

What happens during Directional selection?

Answer 11

In directional selection one of the extreme phenotypes is selected for. the other extreme and average are selected against.
This type of selection occurs due to a change in the environment that favors one of the extreme phenotypes.
The result of directional selection is the shift of a population’s mean value towards the extreme that is being selected for.

Question 12

What happens during disruptive selection?

Answer 12

Both of the extreme phenotypes are selected for and the average phenotype is selected against. This type of selection again occurs in a changing environment.
As a result of disruptive selection the population is split into two distinct groups.

Question 13

What is meant by the term gene transfer?

Answer 13

The transfer of genes from one organism to another

Question 14

What are the two types of gene transfer?

Answer 14

Horizontal and vertical gene transfer

Question 15

What is meant by vertical gene transfer?

Answer 15

The transfer of genes down from parent to offspring, this occurs either by sexual or asexual reproduction and happens in both prokaryotes and eukaryotes.

Question 16

How are genes transferred vertically in eukaryotes?

Answer 16

by sexual reproduction, genes are passed down from parent to offspring in this way. The genomes of both parents will be different and the genes that are inherited by each offspring will be different hence there will be variation down the generations in eukaryotes through vertical gene transfer

Question 17

How are genes transferred vertically in prokaryotes?

Answer 17

by asexual reproduction such as mitosis or binary fission, in this way offspring have exactly the same genome as their parent. no variation down generations by vertical gene transfer in prokaryotes

Question 18

What is meant by horizontal gene transfer?

Answer 18

Genes are transferred across from one cell to another within the same generation, in prokaryotes this is done as bacteria can exchange plasmids horizontally between members of the same population.

Horizontal gene transfer results in variation within a species of bacteria.

Horizontal exchange of genetic material can result in rapid evolutionary change in a species.

Question 19

Does natural selection occur faster in eukaryotes or prokaryotes and explain your answer?

Answer 19

Natural selection occurs faster in prokaryotes because they can partake in horizontal gene transfer, this results in faster evolutionary change than in vertical gene transfer. This horizontal gene transfer allows natural selection to occur more rapidly in prokaryotic cells.

Question 20

What is a species?

Answer 20

A species is a group of organisms that is capable of interbreeding to produce fertile offspring, and which does not normally breed with other groups.

Question 21

What is a gene pool?

Answer 21

the sum total of all the different genes of a particular species, if there are changes in the gene pool then evolution will occur.

Question 22

What is speciation?

Answer 22

the generation of a new biological species by isolation, mutation, and selection.

Question 23

What is meant by the term isolation in terms of evolution?

Answer 23

Isolation occurs when two subpopulations of the same species become isolated from each other, this is vital as it ensures that there is no gene flow between the sub populations.

Question 24

What are the different types of speciation?

Answer 24

• Allopatric speciation
• Sympatric speciation

Question 25

What is meant by allopatric speciation?

Answer 25

Speciation in which gene flow is prevented by a geographical isolation barrier. (river, mountain, desert) This type of speciation occurs in different habitats.

Question 26

What is meant by Sympatric speciation?

Answer 26

Speciation that occurs when two species arise within the same habitat. For this to occur other isolation barriers must be in place to prevent the gene flow between the sub populations. These isolation barriers are behavioral or ecological.

Question 27

Which type of speciation is promoted by disruptive selection?

Answer 27

Sympatric speciation, as both extremes within the population are selected for hence each extreme will split into a sub-population within the same habitat and behavioral and ecological barriers will form over time between the sub populations preventing gene flow.

Question 28

Over what timeframe does evolution and speciation occur?

Answer 28

Over a very long time,
as mutations must arise in each sub population and, different types of selection will occur in each population.

This is true for vertical gene transfer, however in bacteria this process can occur rapidly due to them being able to exchange plasmids in horizontal gene flow.

Question 29

define evolution?

Answer 29

The changes in organisms over generations as a result of genomic variations within a species.

Question 30

What must be true for speciation to occur?

Answer 30

The gene flow between sub-populations must be prevented by an isolation barrier.