9A - Gene Pool

Gene Pool: Collection of all genes and alleles within specific population - can be represented by allele frequencies (proportion of certain alleles)

Allele frequencies: The % of one allele of a gene compared to all other alleles of the same gene

Large gene pool means more genetic diversity

Mutations: Introduce new alleles via changes to DNA (changes can occur spontaneously or by mutagens (e.g. UV radiation, heavy metal, pesticides)

• Substitution

• Addition

• Deletion of single nucleotide bases (point mutation) or DNA blocks (block mutation)

  Mutation classification:

• Advantageous (enhance survivability)

• Deleterious (producion of abnormally functioning protein)

• Neutral

• Mutation in germline cells —> heritable

• Mutation in somatic cells —> not heritable

• Point mutation subtypes:

• Silent mutation: Degenerate nature of code with no effect

• Missense mutation: Substitution by changing code for single amino acid

• Nonsense mutation: Substitution end translation of a gene’s mRNA (codes for a stop codon)

• Frameshift mutation: Addition or minus of one or two nucleotides which alters readind frame (triplets) and causes disruption

• Block mutation subtypes:

• Definition: Alternation of structure of a chromose by deleting, duplicating, inverting, translocating nucleotides which occurs during meiosis

• Aneuploids: Chromosomal abnormality in which an organism possesses incorrect total chromosomes

• Polypoids: Incorrect sets of chromosomes (entire sets of chromosomes lost or gained)

9B- Environmental selection pressures

Selection pressures: Factors within the environment that influence the survivability of a species within an environment (examples: predation, disease, competition, climate change)

• Biological: Sexual selection, predation, infectious disease

• Physical: Climate change, food shortage

• Chemical: Pollutants in water and soil, drugs

  Increasing allele frequency of alleles which code for advantageous phenotypes

  Natural selection: When allele frequencies in a populations gene pool change due to an environmental selection pressure, creating a selective advantage for particular phenotypes

  Conditions of natural selection:

• Variation: Individual varying geneticially - phenotypic differences

• Selection pressures: Impacts survivability of organisms within a population and their ability to reproduce

• Selective advantage: Fitter phenotypes

• Heretiablity

Genetic diversity: Increase of advantageous alleles decreases genetic diversity

9C - Genetic drift and Gene flow

Genetic drift: Involves changes to a populations allele frequencies due to sudden and random occurences

Bottleneck effect: Large prtion of population wiped out by random event (natural disaster) - unique alleles lost means lower gentic diversity

Founder effect: Unrepresentative sample of individuals seperates from larger population to colonise new region and start new population - lower genetic diversity means inbreeding/lower adaptive potential

Gene flow: Introduction or removal of alleles between populations through either migration or interbreeding

• Migration: Can occur when populations are physically close together (immigration and emigration)

• Emmigration: movement out of a population

9D - Speciation

Speciation: The process by which populations genetically diverge until they become distinct species

Pre-zygotic isolation: Barriers between animals in ability to find a partner to mate with. Genetals are not compatible

Post-zygotic isolation: Operate after transfer of the sperm from male to female and are due to chromosomal and chemical imbalances between species.

• Recognised as different species if the can no longer interbreed with each other to produce viable and fertile offspring

• Recognised by comparing genetic composition through analysis of amino acid and DNA sequences

Allopatric speciation: Formation of new species as a result of a geographical barrier

1. Geographical barrier formed (mountain/river) and seperates population, preventing gene flow

2. Different selection pressures act upon each population favouring different phenotypes and allowing for genetic diversity to accumalate

3. Two populations can no longer interbreed to produce offspring due to suffcient genetic differences

   Example: Galapagos finches (seperated islands)

Sympatric speciation: Formation of new species in populations in same location

• Selection pressures act on different phenotypes

• Arise from genetic abnormalities during gamete formation producing polypoid variants (additional chromosome)

  Example: Howea plants (difference in soil)

9E - Selective Breeding

Selective breeding: Humans can selectivelydevelop desirable traits in plants and animals by altering the breeding process of a population

Requirment of selective breeding:

1. Variation

2. Selection pressures

3. Selection advantages

4. Heritability

• Selective breeding: Artifical and created by humans

• Natural selection: Environmental an naturally occuring

Selective breeding on genetic diversity

• Can lead to smaller gene pools and overexpression of deleterious alleles which can reduce adaptibility and fitness within population

• If poor breeding practices are implemented, selective breeding can cause human induced bottleneck

  • In large populations: Small percentage express traits desired by humans by reducing allele frequency will decrease

  • Reducing genetic diversity can lead to increased interbreeding which can increase deleterious alleles and lower adaptive potential

9F - Evolving Pathogens

Bacterial resistance to antibiotics

• Overuse of antibiotics has led to antibiotic resistant bacteria

  • Caused by natural selection - exposure to antibiotics serves as an environmental selection pressure

• Random mutations make certain bacteria resistant

  Antigenic Drift: Mutations in viruses can often cause changes to antigens - This cause in shape can make immune defences acquired less effective

  (more common in RNA due to no proof reading of bases)

  Antegenic Shift: Two different strands infect same individual at same time RNA antigens get shuffled - virus particles get new combinations

  (common in retroviruses such as influenza)