Gene Pools Flashcards
Species
Group of individuals that share many characteristics and are able to interbreed under natural conditions to produce fertile offspring.
Population
Group of organisms of the same species living together in a particular place at a particular time.
Evolution
The gradual change in the characteristics of a species overtime.
Variation
Differences that exist between individuals or populations of a species. (Mutations, random fertilisation, non-disjunction, crossing over, recombination and independent assortment).
Gene pools
Available genes to a population.
Allele frequency
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.
What are gene mutations
Changes in a single gene so that the traits normally produced by that are changed or destroyed.
How does a gene mutation occur
- Occur during DNA replication, through:
› Substitutions: One base replaces another, (transitions or transversions).
› Frame Shifts: One base is removed or added, (insertion or deletion).
Point mutation
A change in just one base. This could alter the protein produced.
Somatic mutation
A change in a gene in the normal body cells. It is not inherited.
Germline mutation
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.
What are chromosomal mutations
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.
What can cause a chromosomal mutation
deletion duplication inversion translocation non-disjunction
Deletion
Part of a chromosome is lost.
Duplication
A section of a chromosome occurs twice. This may happen if a chromatid breaks off and joins on to the wrong chromatid.
Inversion
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.
Translocation
Part of a chromosome breaks of and is re-joined to the wrong chromosome.
Non-disjunction
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).
What do mutagenic agents do
- Alter the DNA
- Affect the cells ability to reproduce.
- Cause cell death/apoptosis.
- Cause cells with faulty DNA reproduce (cancer).
Examples of mutagenic agents
radiation, certain medicines, viruses, x-rays.
Darwins theory of evolution
- 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.
What is random genetic drift
- 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.
The founder effect
- 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.
What is natural selection, what is it based on
- 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.
Struggle for existence
There is competition within and between species to obtain enough resources to exist/survive.
What is a selective agent
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.
Evolution and natural selection
› 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.
What is sickle cell anaemia
- 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.
Selection advantage of sickle cell
- 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.
Sickle cell in a gene pool with no selective agent
› 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.
Sickle cell persisting
› 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.
