Gene Pools

Question 1

Species

Answer 1

Group of individuals that share many characteristics and are able to interbreed under natural conditions to produce fertile offspring.

Question 2

Population

Answer 2

Group of organisms of the same species living together in a particular place at a particular time.

Question 3

Evolution

Answer 3

The gradual change in the characteristics of a species overtime.

Question 4

Variation

Answer 4

Differences that exist between individuals or populations of a species. (Mutations, random fertilisation, non-disjunction, crossing over, recombination and independent assortment).

Question 5

Gene pools

Answer 5

Available genes to a population.

Question 6

Allele frequency

Answer 6

How often do alleles occur in the gene pool. If frequency changes substantially can cause change in species. Mutations can cause a change in the gene pool.

Question 7

What are gene mutations

Answer 7

Changes in a single gene so that the traits normally produced by that are changed or destroyed.

Question 8

How does a gene mutation occur

Answer 8

• Occur during DNA replication, through:
  › Substitutions: One base replaces another, (transitions or transversions).
  › Frame Shifts: One base is removed or added, (insertion or deletion).

Question 9

Point mutation

Answer 9

A change in just one base. This could alter the protein produced.

Question 10

Somatic mutation

Answer 10

A change in a gene in the normal body cells. It is not inherited.

Question 11

Germline mutation

Answer 11

A change in the hereditary material in the egg or sperm that becomes incorporated into the DNA of every cell in the body of the offspring.

Question 12

What are chromosomal mutations

Answer 12

Involves all of a part of a chromosome and therefore affect not just one but a number of genes. Chromosomal mutations cause abnormalities so severe that miscarriage often occurs early in the pregnancy.

Question 13

What can cause a chromosomal mutation

Answer 13

deletion
duplication 
inversion 
translocation 
non-disjunction

Question 14

Deletion

Answer 14

Part of a chromosome is lost.

Question 15

Duplication

Answer 15

A section of a chromosome occurs twice. This may happen if a chromatid breaks off and joins on to the wrong chromatid.

Question 16

Inversion

Answer 16

Breaks occur in a chromosome and the broken piece joins back in, but the wrong way around. This changes the order of genes on the chromosome and may disrupt the pairing of homologous chromosomes during meiosis.

Question 17

Translocation

Answer 17

Part of a chromosome breaks of and is re-joined to the wrong chromosome.

Question 18

Non-disjunction

Answer 18

During meiosis, a chromosome pair does not separate and one daughter cell has an extra chromosome and one has a missing chromosome. These are sometimes referred to as aneuploidy (a change in chromosome number).

Question 19

What do mutagenic agents do

Answer 19

• Alter the DNA
• Affect the cells ability to reproduce.
• Cause cell death/apoptosis.
• Cause cells with faulty DNA reproduce (cancer).

Question 20

Examples of mutagenic agents

Answer 20

radiation, certain medicines, viruses, x-rays.

Question 21

Darwins theory of evolution

Answer 21

• There are more individuals born, than what can survive.
• There is a struggle for existence/competition as there is not enough resources for everyone.
• The fittest will survive, breed and pass on their alleles. Therefore, is the environment changes/selection pressures change, different individuals may be better suited, causing a change in the species.

Question 22

What is random genetic drift

Answer 22

• A random change in a species. Population must be small to have an effect.
  › An individual dies, some alleles are lost from the gene pool, causing a change in subsequent generations.

Question 23

The founder effect

Answer 23

• A small group breaks away from the main population and starts a new population. May only take a small portion of the gene pool so species develop differently.

Question 24

What is natural selection, what is it based on

Answer 24

• The process by which a species becomes better adapted to its environment; those individuals with favourable characteristics have a survival advantage and pass on these characteristics onto subsequent generations.
• Based on Darwin’s, survival of the fittest, organisms best suited to the environment survive, breed and pass on their alleles.

Question 25

Struggle for existence

Answer 25

There is competition within and between species to obtain enough resources to exist/survive.

Question 26

What is a selective agent

Answer 26

Factor that causes death of individuals with a particular characteristic, but has no effect on those without the characteristic or a factor that favours certain characteristic and organisms without that characteristic will die.

Question 27

Evolution and natural selection

Answer 27

› When selection pressures change, different organisms/phenotypes may be better suited therefore it will survive, breed and pass on there alleles. The original species are ‘not selected’ anymore, so its alleles begin to reduce in frequency. This results in a change in the gene pool/allele frequencies which can result in a change in a species. This is evolution.

Question 28

What is sickle cell anaemia

Answer 28

• A lethal recessive disease, two alleles must be inherited from both parents for the offspring to inherit the disease. If two are inherited, results in death.
• Causes red blood cells to become c-shaped (sickled), this reduces their ability to carry oxygen.

Question 29

Selection advantage of sickle cell

Answer 29

• This provides a selection advantage to carriers of sickle cell anaemia, in areas with malaria. The c-shape prevents the malaria parasite taking over the red blood cells and killing it.

Question 30

Sickle cell in a gene pool with no selective agent

Answer 30

› In a gene pool with no selective agent. People who get sickle cell anaemia would die and remove their alleles from the gene pool. Therefore, the number of sickle cell alleles will decrease, eventually numbers would get so low, it would be unlikely for carriers to meet, removing the disease from the gene pool.

Question 31

Sickle cell persisting

Answer 31

› If a lethal recessive disease persists in a population there must be a reason. Being a carrier must provide a selection advantage. People who are carriers for sickle cell are protected against malaria and therefore they will survive breed and pass on alleles, keeping sickle cell allele frequency constant in population.