6.2 Variation and evolution (Combined)

Question 1

What is variation?

Answer 1

Differences in the characteristics of individuals in a population is called variation

Question 2

What are the causes of variation within a species?

Answer 2

● Genetics

● Environment

● A mixture of both of the above

Question 3

What is genetic variation?

Answer 3

● Variations in the genotypes of organisms of the same species due to the presence of different alleles

● Create differences in phenotypes

Question 4

What creates genetic variation in a species?

Answer 4

● Spontaneous mutations

● Sexual reproduction

Question 5

What is a mutation?

Answer 5

A random change to the base sequence in DNA which results in genetic variants. They occur continuously.

Question 6

State the three types of gene mutation

Answer 6

● Insertion
● Deletion
● Substitution

Question 7

How may a gene mutation affect an organism’s phenotype? (3)

Answer 7

● Neutral mutation does not change the sequence of amino acids. Protein structure and function are the same. No effect on the phenotype

● Mutation may cause a minor change in an organism’s phenotype e.g. change in eye colour

● Mutation may completely change the sequence of amino acids. This may result in a non-functional protein. Severe changes to
phenotype.

Question 8

What is the consequence of a new phenotype caused by a mutation being suited to an environmental change?

Answer 8

There will be a rapid change in the species

Question 9

What is evolution?

Answer 9

● A gradual change in the inherited traits within a population over time

● Occurs due to natural selection which may result in the formation of a new species

Question 10

Outline the theory of natural selection

Answer 10

All species of living things have evolved from simple life forms that first developed more than 3 billion years ago.

1. Genetic variation exists due to spontaneous mutations
2. Selection pressures (e.g. competition, disease) exist
3. Random mutation gives an organism a selective advantage
4. The organism is better adapted into the environment and survives
5. The organism reproduces passing on its beneficial alleles
6. Frequency of advantageous alleles increase

Question 11

How do two populations become different species?

Answer 11

When their phenotypes become different to the extent that they can no longer interbreed to produce fertile offspring

Question 12

What is selective breeding?

Answer 12

The process by which humans artificially select organisms with desirable characteristics and breed them to produce offspring with similar phenotypes

Question 13

Outline the main steps involved in selective breeding

Answer 13

1. Identify a desired characteristic (e.g. disease resistance)
2. Select parent organisms that show the design traits and breed them together
3. Select offspring with the desired traits and breed them together
4. Process repeated until all offspring have the desired traits

Question 14

Give examples of characteristics selected for in selective breeding

Answer 14

● Disease resistance in crops

● Higher milk or meat production in animals

● Gentle nature in domestic dogs

● Large flowers

Question 15

What is the main advantage of selective breeding?

Answer 15

Creates organisms with desired features:

● Crops produce a higher yield of grain

● Cows produce a greater supply of milk

● Plants produce larger fruit

● Domesticated animals

Question 16

Other than in agriculture, where else is selective breeding useful?

Answer 16

● In medical research

● In sports (e.g. horse racing)

Question 17

Outline the disadvantages of selective breeding.(4)

Answer 17

● Reduction in the gene pool which will come (especially harmful if sudden and environmental change occurs)

● Inbreeding results in genetic disorders

● The development of other physical problems (e.g. respiratory problems in bulldogs)

● Potential to unknowingly select harmful recessive alleles

Question 18

What is genetic engineering?

Answer 18

The modification of the genome of an organism by the insertion of a desired gene from another organism.

Genes from chromosomes of humans and other organisms can be cut out and transferred to cells of other organisms.

This enables the formation of an organism with beneficial characteristics.

Question 19

Give an example of uses for genetically modified plants

Answer 19

● Disease resistance

● Produce larger fruits

Question 20

What is a use for genetically modified bacterial cells?

Answer 20

To produce human insulin to treat diabetes

Question 21

Describe the benefits of genetic engineering. (3)

Answer 21

● Increased crop yields for growing population (e.g. herbicide resistance, disease resistance)

● Useful in medicine e.g. insulin producing bacteria, antithrombin in goat milk, possibility to overcome some inherited disorders (being explored in medical research)

● GM crops produce scarce resources e.g. GM golden rice produces beta- carotene (source of vitamin A in the body)

Question 22

Describe the risks of genetic engineering. (4)

Answer 22

● Long-term effects of the consumption of GM crops unknown

● Negative environmental impacts e.g. reduction of biodiversity, impact on the food chain, contamination of non-gm crops forming ‘superweeds’

● Late onset health problems in GM animals

● GM seeds are expensive LEDCs may be unable to afford them or maybe become independent on businesses that sell them

Question 23

What is the name for crops that have had their genes modified?

Answer 23

Genetically modified (GM) crops e.g. those modified to be resistant to insect attack and herbicides

Question 24

What is Bacillus thuringiensis (Bt)?

Answer 24

● Insect larvae are harmful to crops

● Bt is a bacterium which secretes a toxin that kills insect larvae

Question 25

How is genetic engineering used to protect crops against insects?

Answer 25

● The gene for toxin production in Bt can be isolated and inserted into the DNA of crops

● Bt crops now secrete the toxin which kills any insect larvae that feed on it

Question 26

What are the benefits of Bt crops? (3)

Answer 26

● Increased crop yields (fewer crops damaged)

● Lessens the need for artificial insecticides

● Bt toxin is specific to certain insect larvae so it’s not harmful to other organisms that ingest it

Question 27

What are the risks of Bt crops? (3)

Answer 27

● Long-term effects of the consumption of Bt crops are unknown

● Insect larvae may become resistant to the Bt toxin

● Killing insect larvae reduces biodiversity

Question 28

Describe the process of genetic engineering. (Higher)

Answer 28

1. DNA is cut at specific base sequences by restriction enzymes to create sticky ends
2. Vector DNA cut using the same restriction enzymes to create complementary sticky ends
3. Ligase enzymes join the sticky ends of the DNA and vector DNA forming recombinant DNA
4. Recombinant DNA mixed with and ‘taken up’ by target cells

Question 29

What is a vector? (Higher)

Answer 29

A structure that delivers the desired gene into the recipient cell (e.g. plasmids, viruses)