Variation And Evolution

Question 1

Variation

Answer 1

Differences within a population

Question 2

Species

Answer 2

A group of organisms capable of interbreeding to produce fertile offspring

Question 3

Classification

Answer 3

Grouping organisms based on specific characteristics

Question 4

Causes of variation

Answer 4

•Sexual reproduction- meiosis, fertilisation of gametes, independent assortment
•Mutations

Question 5

Mutations

Answer 5

Changes in amount or structure of dna

Question 6

Causes of mutation (mutagens)

Answer 6

•Radiation eg. ultraviolet radiation from the sun
•Chemicals eg. benzene
•Viruses eg. Epstein-Barr virus can cause mutations resulting in Burkitt’s lymphoma (a cancer)

Question 7

Gene/point mutations

Answer 7

A change in a single base pair within a gene, e.g. haemophilia

Question 8

Chromosome mutations

Answer 8

A change in the structure a chromosome or a change in the number of copies of a particular chromosome e.g. Triple X syndrome (a female with Triple X syndrome will have 3 X chromosomes in each cell instead of 2)

Question 9

Evolution

Answer 9

Inheritable changes within a species in response to the environment over a long period of time

Question 10

Who presented Theory of natural selection

Answer 10

Darwin and Wallace

Question 11

What is theory of natural selection

Answer 11

They observed that there are large numbers of offspring produced, but the population size stays the same overall i.e. not all offspring survive.
• Their explanation:
• There is competition between organisms for a limited resource (e.g. territory, mates, food, water).
• There is variation within species i.e. members of the same species have different characteristics that may make them better/worse suited to winning the competition for the limited resource.
• The better adapted organisms for this competition survive, while the less adapted organisms die. (Survival of the fittest)
• The better adapted organisms interbreed and pass on this adaptation to their offspring.
• Over time, this adaptation becomes more common, causing the non-adapted organisms to disappear from the population.

Question 12

Evidence of evolution

Answer 12

Fossils: fossils show differences when compared with modern organisms

Embryology: Different organisms have similar embryo stages i.e. they have a common ancestor

Anatomy: Different species have similar anatomical structures e.g. limbs, but these limbs are specifically adapted for the survival of that species. For example humans have hands for gripping and tool use, whereas dolphins have broader ‘limbs’ for swimming

•Biochemistry- Different species have similar metabolisms

Question 13

What is meant by the term evolution

Answer 13

The genetic changes in a population over time in response to the environment

Question 14

Outline the theory of evolution by natural selection

Answer 14

There is competition between species
-The more adapted members survive (survival of the fittest)
-The organisms that do not have the adaptation die
-The adapted members interbreed and pass on this adaptation to the offspring
-This gives the offspring the adapted genotype
-Over time this adaptation becomes more common
-The genotype of the population has changed

Question 15

Describe evidence in support of evolution from one named source.

Answer 15

Fossils: more modern fossils are more complex, showing that there have been changes in the genotypes of the population, causing the population to have different characteristics and features

Question 16

In the context of natural selection, explain how numbers in a population remain relatively constant despite the production of many offspring

Answer 16

-In a population, there is competition between members for scarce resources, such as food, water, shelter.
-There are genetic differences (different genotypes) between members in a population.
-The members of a population who are best adapted to the environment survive. The members who are not adapted die out.
- The adapted organisms reproduce and their offspring also carries the adaptation.
-The rate at which organisms are dying out is equal to the rate at which offspring is being produced
(birth rate = death rate). Therefore, the population remains constant.

Question 17

Name either of the scientists responsible for the Theory of Natural Selection

Answer 17

Charles darwin

Question 18

Explain the following terms as used in genetics: species, variation.

Answer 18

A species is a group of similar organisms that are capable of interbreeding with each other, but not with other such groups, to produce fertile offspring.

Variation means that there are differences between members of a species.

Question 19

Give one cause of genetic variation.

Answer 19

Sexual reproduction

Question 20

Give an account of the Theory of Natural Selection. Name the scientists who are associated with the theory and refer to any one observation that prompted its development.

Answer 20

The theory of evolution by means of natural selection is based on 3 observations and two conclusions derived from these observations.

They were coined by Charles Darwin and Alfred Russel Wallace.

They observed that inherited variations occur in populations and that these variations may arise from sexual reproduction, mutations and also genetic engineering.

Thus, they have concluded that there is a struggle for existence and if more offspring are produced, then the environment cannot support them all, meaning competition for resources will occur.

They also concluded that these organisms that have variations will enable them to adapt better to their environment, therefore surviving and reproducing.

• They will pass their variations onto the next generation and organisms with unfavourable variations will not survive.