Topic 4: Variation: Genetic Diversity

Natural selection – 4 stages

1. Variation

2. Selection pressure – who lives who dies due to change

3. Adaptation – leading to variable survival

4. Reproduction – pass on advantageous alleles

Variation (driven by mutation)

Random mutations, new alleles created, genetic diiversity increases

Selection pressure

• Environmental changes occur

• Predatation levels rise

• Disease breaks out

• Competition for resources heightens

Adaptation

Certain alleles become advantageous, Possesses beneficial phenotypes, these individuals are more likely to survive, overcome the specific environmental selection pressure

Reproduction

Pass on advantageous alleles, allele frequency increases over many generations

An allure is a variant form of a gene.

Different alleles can result in different observable traits

Genetic diversity is the total number of different alleles in a population.

This leads to variation as different combinations of alleles means different proteins are produced, resulting in different characteristics

Genetic diversity influences natural selection as organisms with advantageous traits are more likely to survive, reproduce, and pass on their alleles, influencing the gene pool

The more successful and organism is at a reproducing, the more likely its alleles will be passed onto the next generation, increasing the allele frequency

Directional selection

Shifts the curve in the direction of the favoured extreme, extreme phenotype. E.g. being larger is useful to not be prayed on, so alleles for taller heights favoured, Being antibiotic resistant is advantageous so Population tends to have high proportion of antibiotic resistant alleles

Disruptive selection

Extreme ends of spectrum are both advantageous. It is the middle ground that does not offer an advantage. Middle ground is therefore selected against. E.g. camouflage – light and dark or big and small within a species, like mice.

Stabilised selection

This is where extremes are bad, middle is more advantageous. Average phenotype is favoured, narrows the curve i.e. low birth mass – too low baby dies, too large birthing difficulties.

Genetic diversity

The total number of different alleles in a population

How can genetic diversity be increased?

• crossing over

• Mutation

• Random fertilisation

• Independent segregation

The process of natural selection includes these key steps

1. There is variation in characteristics within a species

2. More genetic variation emerges within a population due to random mutations

3. Individual with alleles that code for traits that are advantageous for survival are more likely to reproduce

4. These advantageous alleles are passed down to offspring

5. Overtime, these beneficial alleles become more common in the population

This mechanism leads to populations becoming more adapted to their environment over generations

Natural selection is an ongoing process that enables organisms to adapt to environmental changes

How antibiotic resistance arises

1. Some bacteria develop random mutations that provide resistance to antibiotics

2. When antibiotics are used, only the resistant bacteria survived, while the others die off

3. The resistant bacteria reproduce, passing on resistant alleles to their offspring

4. Overtime the proportion of resistant alleles increases, leading to mostly resistant bacteria

Antibiotics

• inhibit DNA synthesis

• Inhibit protein synthesis – 70s Ribosomes

• Inhibit or destroy cell walls

Mutations can alter conditions to prevent antibiotics from working

1. Changes protein on membrane – Preventing entry

2. ‘Pump’ To remove chemicals from the cell

3. Enzymes to destroy antibiotics

4. Alterations of protein that the antibiotic would have bound to so can no longer bind

This resistance complicates treatment options, increases healthcare costs

And raises mortality rates in humans