Variation and Evolution

Question 1

What is heritable variation?

Answer 1

Heritable variation is caused by differences in genes and so can be passed on from parent to child e.g. hair/eye colour

Question 2

What causes heritable variation? (DNA explanation)

Answer 2

Differences in the genotypes of organisms of the same species due to the presence of different alleles. It creates differences in phenotypes.

Question 3

What is environmental variation?

Answer 3

Environmental variation is caused by the environment in which the organisms has developed. E.g. scars, piercings from diet, lifestyle, climate

Question 4

What is continuous variation?

Answer 4

Continuous variation is where there is a continuous range with no ‘categories’ e.g. height, weight

Question 5

What is discontinuous variation?

Answer 5

Discontinuous variation is where there are distinct groups e.g. gender, eye colour, blood group

Question 6

What causes differences in offspring?

Answer 6

Offspring are genetically different from their parents as a result of sexual reproduction which involves an egg fusing with a sperm in the process of fertilisation. Meiosis produces genetically different gametes.

Question 7

What happens during fertilisation?

Answer 7

One gamete from each parent fuses to form a zygote. Genetic information is mixed to form a unique individual.

Question 8

What is a zygote?

Answer 8

Full set of chromosomes

Question 9

What does asexual reproduction do?

Answer 9

Asexual reproduction does not create genetic variation as it involves mitosis which produces genetically identical daughter cells known as clones.

Question 10

What is a mutation?

Answer 10

A random change in the structure of a gene.

Question 11

What can cause a mutation?

Answer 11

A variety of factors e.g. exposure to some chemicals and ionising radiation.

Question 12

What happens to mutations in gametes?

Answer 12

They will be passed on to the next generation

Question 13

What happens to mutations in body cells?

Answer 13

They will not be passed on to the next generation.

Question 14

What may mutations cause?

Answer 14

Mutations may cause a complete change in the sequence of amino acids. This could result in a non-functional protein and severe changes to phenotypes. (formation of harmful alleles)

Question 15

What is cystic fibrosis?

Answer 15

A recessive condition resulting in the production of sticky mucus that affects the lungs and digestive system which makes breathing and digestion difficult.

Question 16

What does it mean for the CF gene to be recessive?

Answer 16

The disease only appears when an individual has the allele for this gene on both chromosomes.

Question 17

Some people have one CF allele and one “normal” allele. What does this mean?

Answer 17

These people are heterozygous for the recessive CF trait and will not suffer from the disease but can pass it on to any children they have. These people are called carriers.

Question 18

What is gene therapy?

Answer 18

The name given to a range of techniques that can be used to remove the effects of a harmful allele.

Question 19

What 2 methods of gene therapy are there?

Answer 19

Introducing a “healthy” allele into the person’s DNA.
“Switching off” the harmful allele.

Question 20

What does introducing a healthy allele into the person’s DNA do?

Answer 20

It replaces the faulty allele and if the harmful allele is recessive a healthy dominant allele will counteract it. The recessive allele does not have to be removed.

Question 21

What does “switching off” a harmful allele do?

Answer 21

This can be done in various different ways including the introduction of a completely new gene into the body.

Question 22

What are the ethical issues of gene therapy?

Answer 22

The process is very expensive.
Some religious groups believe that humans should never alter the genes of living organisms.

Question 23

What is evolution?

Answer 23

The process by which living species have gradually changed and developed from earlier forms over a long period of time.

Question 24

What does evolution result in?

Answer 24

Organisms becoming better adapted to their environment.

Question 25

Who proposed the theory of natural selection?

Answer 25

Charles Darwin and Alfred Russel Wallace in 1858

Question 26

What is natural selection?

Answer 26

• All populations vary due to past mutations
• Most organisms reproduce therefore there is competition
• Variations are more likely to survive better in their environment
• The organisms that survive breed and pass on their genes
  -The next generation will have more of the beneficial variations and the beneficial characteristics become more common eventually spreading
  Species then evolve

Question 27

Common limitations of models of natural selection?

Answer 27

Object doesn’t move - Prey move
Only one colour - Environment is not one colour and prey are more similar in colour

Question 28

What does extinction mean?

Answer 28

When a species becomes extinct all members of the species have died.

Question 29

What can cause extinction?

Answer 29

The organism has failed to adapt quickly enough to its environment.
Outcompeted by better adapted species
The environment suddenly changes.

Question 30

What can cause a superbug?

Answer 30

When natural selection happens very quickly.

Question 31

What is a superbug?

Answer 31

These are bacteria that have become resistant to the antibiotics normally used to treat infections.

Question 32

How does taking antibiotics create superbugs?

Answer 32

When you take antibiotics there will always be a few bacteria that are naturally resistant and will survive. This can lead to the resistant ones to multiply given time, the whole population of bacteria will be resistant to the antibiotic.

Question 33

Natural selection is rapid in bacteria because…

Answer 33

They reproduce very rapidly and the level of exposure to antibiotics is very high because a huge number of antibiotics are used.

Question 34

What is causing an increase in bacterial resistance to antibiotics?

Answer 34

Overprescription and antibiotic misuse.

Question 35

What is the genome?

Answer 35

The name given to all the genetic information in an organism. It includes all the genes and their sequence on all the chromosomes and th DNA base pairs that make up those genes.

Question 36

What is the Human Genome Project?

Answer 36

An international scientific research project that worked out the sequence of chemical base pairs in human DNA, identifying all the genes.

Question 37

When was the Human Genome Project completed?

Answer 37

2003

Question 38

How is the Human Genome Project extremely important?

Answer 38

Some genes are known to directly cause disease and knowing their existence and location allows the possibility of altering them or counteracting their effects.
Allows the possibility of creating targeted drugs or viruses that would attack cells containing a mutated cancer-causing gene.