mutations and speciation

Question 1

define mutation

Answer 1

A permanent change in the DNA sequence

Question 2

define mutagen

Answer 2

anything that causes a mutation e.g. radiation, poisons, diet and viruses

Question 3

define somatic mutations

Answer 3

mutations that occur in normal body cells. These cannot be passed to offspring

Question 4

define germline mutations

Answer 4

occur in gametes (egg or sperm) and can be passed to offspring

Question 5

define point mutations

Answer 5

changes to 1 – 3 nucleotides

Question 6

define chromosomal mutations

Answer 6

changes to large sections of the DNA

Question 7

define silent mutations

Answer 7

changes to the DNA that have no effect on the individual. This is because the changes in sequence still codes for the same amino acids, which is still functional, or it affects a portion of DNA that isn’t being read by the cell.

Question 8

define missense mutations

Answer 8

changes to DNA that put the incorrect amino acids into the protein. This may end up being harmful or very occasionally beneficial.

Question 9

define nonsense mutations

Answer 9

result in the stop codon being inserted and the protein not being fully formed (mostly harmful)

Question 10

define frame shift mutations

Answer 10

inserts/deletes one or more nucleotides which moves the order of the rest of the code

Question 11

what are the 4 different types of point mutations

Answer 11

Substitution: swapping one letter for another

Insertion: an extra letter is added in

Deletion: a letter is removed

Inversion: 2 letters are swapped in position

Question 12

what are the 6 different types of point mutations occurring at CHROMOSOMAL LEVEL

Answer 12

Deletion: a portion of the chromosome is removed

Duplication: a section of the chromosome is repeated

Inversion: a section is inverted in its correct locus (location) but backward

Translocation: a portion from 2 chromosomes are swapped with a section of a different chromosome

Nondisjunction: the homologous chromosomes don’t separate correctly, resulting in one daughter cell with 2 chromosomes and the other with none.

Question 13

define evolution

Answer 13

Theory that all living things are descended from previously living, simpler organisms

Process if observed when we see a permanent genetic change to a population’s gene pool.

Question 14

list the six ways how changes to a gene pool are created

Answer 14

Mutation

Natural selection

Random genetic drift

The founder effect

Migration

Isolation and speciation

Question 15

explain what natural selection is

Answer 15

There is variation in a population

Those who possess a trait that gives them a SURVIVAL ADVANTAGE in their environment are more likely to SURVIVE, REPRODUCE and PASS their genes onto the next generation,

INCREASING FREQUENCY of the favourable traits in the next generation

Occurs because:
- More offspring are produced then can survive
to maturity
- There exists significant VARIATION in
characteristics in a population
- Between members of the same species, there
is a ‘STRUGGLE TO EXIST’ or competition for
limited resources

Survival of the fittest: The individuals most likely to survive and reproduce in the struggle for existence are those best suited to the environment
- The favourable feature would become more
frequent in each successive generation
- Similarly, unfavourable characteristics would
not give an individual a selective advantage
and therefore they would be less likely to
survive and pass these on
- The frequency of unfavourable characteristics
in a gene pool should reduce over a number of
generations
- An individual doesn’t change over time but the
frequency of alleles in the population changes
over time.

Question 16

explain what random genetic drift is

Answer 16

happens more often in small populations

breeding is by chance

this can mean that some individuals might not breed at all and their genes are lost

this has a large impact on small populations

small changes would normally be swamped in large interbreeding population

only when populations become isolated will small changes in variation cause them to diverge into new species.

Question 17

explain what the founder effect is

Answer 17

Founder effect is a case of genetic drift, change in allele frequencies in small isolated populations due to random events.

The gene pool of an isolated population will be a random subset of the gene pool of the parent population

Shows that chance events can affect gene frequencies in unexpected ways.

Alleles that are common in the parent population might now be vary rare, or vice versa

Question 18

explain what migration is

Answer 18

The movement of populations, groups or individuals

New individuals may enter a population by migration from another population

If they reproduce within the population, they can bring new alleles to the local gene pool

This is called gene flow

Question 19

explain what isolation is

Answer 19

Isolating mechanism: any factor that acts to reduce or block the flow of genes between two populations

Geographic isolation:

• Physical barriers which prevent interbreeding between populations
• E.g. mountain range, glacier, ocean or island

Sociocultural isolating mechanisms

• Cultural barriers which prevent interbreeding between populations
• E.g. educational background, culture, religion

Question 20

explain what speciation is

Answer 20

Isolating mechanisms provide barriers to gene flow between populations – there are potential pathways for speciation

Species begin when small parts of a larger population are isolated from the parent population

Because they are geographically isolated, members of this small population can only interbreed with one another

Mutation and re-combinations within this isolated population can lead to entirely new varieties, and new combinations of existing traits.

The population may experience genetic drift, a random fluctuation in the proportion of a particular allele in a small, inbred population

Natural selection favours some combinations of alleles over other combinations.

Over time, the effect of natural selection, genetic drift, mutation and recombination can become isolating mechanisms

When the isolated population is reunited with the parent population, they can no longer interbreed. They have become reproductively isolated, and can now be considered a new species

Question 21

give some examples of natural selection in human populations

Answer 21

skin colour

sickle cell anaemia

body types (somatotypes)

Question 22

what are bottlenecks

Answer 22

sharp reduction in the size of a population due to environmental events such as famines, disease and natural disasters.

Such events can reduce the variation in the gene pool of a population, therefore a small population with smaller gene diversity remains to pass on genes to future generations.