6.1 Variation & Evolution

Question 1

Describe how natural selection increases advantageous phenotypes

Answer 1

• Populations of species usually show a lot of genetic variation - this means that there’s a big mix of genetic variants (alleles) present in the population. Genetic variants arise when DNA randomly mutates. Occasionally, a genetic variant can have a big effect on an organism’s phenotype. However, most genetic variants have no effect on phenotype and some of them only have a small influence on a phenotype.
• Those genetic variants that do affect phenotype can give rise to characteristics that make an organism better suited to a particular environment . This means that the organisms that inherit these variants will have an advantageous phenotype.
• The resources living things need to survive are limited. Individuals in a community must compete for these resources to survive. Individuals with genetic variants that give advantageous phenotypes will have a better chance of successfully competing for resources, and so have an increased chance of surviving, reproducing and passing on their genes.

Question 2

What is the definition of evolution?

Answer 2

The change in inherited characteristics of a population over several generations, through the process of natural selection.

Question 3

What is speciation?

Answer 3

Speciation is when a new species is formed. Evolution by natural selection may mean that a species’ phenotype changes so much that a completely new species is formed (i.e. the old and new version of the species wouldn’t be able to breed together to produce fertile offspring).

Question 4

Describe how speciation can happen when a physical barrier isolated two populations of a species

Answer 4

Conditions on each side of the barrier will be slightly different so the phenotypes that are beneficial will be different for each population. Natural selection acts on each population to increase the proportion of the advantageous phenotype in that population, until they are so different that they can no longer breed together.

Question 5

What did Charles Darwin? (2)

Answer 5

• He noticed that there was variation in members of the same species and that those with characteristics most suited to their environment were more likely to survive.
• He also noticed that characteristics could be passed on to offspring.

Question 6

What did Wallace propose?

Answer 6

That evolution by natural selection might lead to the development of new species if populations of the same species become isolated from each other and live in different ecosystems.

Question 7

How has the theory of evolution by natural selection effected our understanding of classification?

Answer 7

If all living organisms have descended from a common ancestor, then we’re all related in some way. We now classify organisms (arrange them into groups) based on how closely related they are.

Question 8

How has the theory of evolution effected our understanding of antibiotic resistance?

Answer 8

We now understand the importance of finishing the course of drugs to prevent resistant bacteria spreading and we know we need to constantly develop new antibiotics to fight newly evolved resistant bacteria.

Question 9

How has the theory of evolution effected our understanding of conservation?

Answer 9

We now understand the importance of genetic variation and how it helps populations adapt to changing environments. This has led to conservation projects to protect species.

Question 10

Continuous and discontinuous variation

Answer 10

• Continuous variation is where the characteristic changes gradually over a range of values, such as height, body mass, and skin colour. These characteristics are usually influenced by multiple genes (polygenic).
• Discontinuous (discrete) variation is where the characteristic has distinct forms, with no overlap. For example, eye colour is discontinuous because you have either blue, green, or brown eyes. These characteristics are usually only influenced by one or two genes.

Question 11

Who was Charles Darwin?

Answer 11

Charles Darwin was a 19th century biologist, who is credited with developing and proposing the theory of evolution.