2.4 Variation and Evolution

Question 1

Continuous variation

Answer 1

continuous range with no categories e.g. height

Question 2

Discontinuous variation

Answer 2

there are distinct groups

Question 3

heritable variation

Answer 3

caused by having different sets of genes as characteristics are controlled by genes

Question 4

variation definition

Answer 4

difference in characteristics between individuals of a species or between species

Question 5

environmental variation

Answer 5

caused by influence of the environment

Question 6

sexual reproduction

Answer 6

egg fuses with sper (fertilisation)
mothers genes are mixed with fathers
this gives rise to variation

Question 7

asexual variation

Answer 7

one individual produces offspring that are genetically identical to it - clones

Question 8

mutation definition

Answer 8

a change in the structure of a gene

Question 9

how is rate of mutation increased

Answer 9

ionising radiation / some chemicals

Question 10

gene therapy defintion

Answer 10

techniques used to remove the effects if a harmful allele
by introducing a healthy dominant allele or ‘switching off’ a harmful one.
Putting copies of the normal allele into the cells of a person who has the disorder

Question 11

Properties of mutations

Answer 11

these changes occur naturally, randomly and often
most have no effect, but some can be beneficial or harmful

Question 12

What is a “carrier” of a genetic disease

Answer 12

Heterozygous for the recessive trait - Cc - carry the faulty allele but appear healthy

Question 13

Problems and ethical issues with gene therapy

Answer 13

problems
- the alleles may not go into every target cell
- the alleles may join with the chromosomes in random places, so they do not work properly
- treated cells may be replaced naturally by the patient’s own untreated cells (not permanent cure)
ethical issues
- research is expensive
- some religious groups believe we shouldn’t alter genetics

Question 14

Why are mutations important

Answer 14

Without them organisms would never change

Question 15

Why is heritable variation important

Answer 15

Without it, species could never become adapted to their environment

Question 16

Limitations of modelling natural selection

Answer 16

• model prey does not move
• with card - background is flat not textured

Question 17

Explaining natural selection - 1- Overproduction - explanation

Answer 17

Most animals and plants have more offspring that can survive - offspring are in a “battle for survival”

Question 18

Explaining natural selection - 2- Variation - explanation

Answer 18

The offspring are not all the same - they show variation

Question 19

Explaining natural selection -3 - survival of the fittest to breed - explanation

Answer 19

Some varieties are better equipped for survival than others - these are more likely to survive to breed

Question 20

Explaining natural selection - 4- breeding - explanation

Answer 20

Those that survive will breed and pass on their heritable characteristics to the next generation (more in this generation will have these characteristics)

Question 21

Explaining natural selection - 5- species evolved - explanation

Answer 21

Over generations the best characteristics have become more common and will eventually spread to all (majority) individuals

Question 22

3 reasons extinction can happen

Answer 22

1- the organism as failed to adapt to its environment (virtually unknown)
2 - The organism has adapted to its environment to some extent, but another similar organism has adapted better. The less successful organism cannot compete and will eventually die out.
3 - The organism has adapted to its environment successfully, but the environment suddenly changes and the organism cannot survive or adapt to the new conditions

Question 23

Antibiotic resistance steps

Answer 23

1- A few bacteria are resistant to the antibiotic
2- Antibiotic is applied
3- Most susceptible bacteria are killed
4-bacteria multiply (increasing resistant numbers)
5- Antibiotic applied again
6- The few remaining susceptible bacteria are killed and the resistant bacteria multiply
7- Antibiotic is now ineffective against resistant bacteria

Question 24

Examples of natural selection happening over a shorter time period (evidence that evolution is ongoing)

Answer 24

Antibiotic resistance in bacteria
Pesticide resistance
Warfarin resistance in rats

Question 25

Explain warfarin resistance in rats

Answer 25

• resistant rats survive and non resistant rats die
• surviving rats have less competition and population grows
• the resistant rats survive to reproduce and pass on their resistant genes so the resistant population grows

Question 26

What is a genome

Answer 26

all the genetic information of an organism

Question 27

Why is human genome mapping important

Answer 27

Some genes cause or increase susceptibility to certain diseases
Knowing the location of these genes allows us to alter them, counteract their effects, or create new and targeted forms of treatment