mutations and speciation Flashcards
define mutation
A permanent change in the DNA sequence
define mutagen
anything that causes a mutation e.g. radiation, poisons, diet and viruses
define somatic mutations
mutations that occur in normal body cells. These cannot be passed to offspring
define germline mutations
occur in gametes (egg or sperm) and can be passed to offspring
define point mutations
changes to 1 – 3 nucleotides
define chromosomal mutations
changes to large sections of the DNA
define silent mutations
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.
define missense mutations
changes to DNA that put the incorrect amino acids into the protein. This may end up being harmful or very occasionally beneficial.
define nonsense mutations
result in the stop codon being inserted and the protein not being fully formed (mostly harmful)
define frame shift mutations
inserts/deletes one or more nucleotides which moves the order of the rest of the code
what are the 4 different types of point mutations
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
what are the 6 different types of point mutations occurring at CHROMOSOMAL LEVEL
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.
define evolution
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.
list the six ways how changes to a gene pool are created
Mutation
Natural selection
Random genetic drift
The founder effect
Migration
Isolation and speciation
explain what natural selection is
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.
explain what random genetic drift is
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.
explain what the founder effect is
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
explain what migration is
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
explain what isolation is
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
explain what speciation is
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
give some examples of natural selection in human populations
skin colour
sickle cell anaemia
body types (somatotypes)
what are bottlenecks
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.
