AOS 3 - Biology - Adaptations

Define gene pools

Gene pools are the complete set of all genes and alleles present within a particular population or species

What is the importance of a diverse gene pool?

Larger gene pools will contain a variety of genes and alleles, leading to a greater number of genotypes and phenotypes resulting in increased genetic diversity

Define mutations

Mutations involve permanent changes to the DNA sequence of an individual

What factors cause mutations?

Radiation (UV (from sunlight), X-rays)

Infectious Agents (Viruses, Bacteria)

Chemicals (Carcinogens (cigarettes), Processed foods + preservatives, Cosmetics + cleaning products)

How can mutations be catergorised?

As advantageous, neutral or disadvantageous based on the mutation’s overall effect on the survivability of the individual.

Where do mutations need to occur to make them heritable?

They need to occur in an individual’s germline cells (cells that generate gametes (sex cells), not somatic cells (body cells) as gametes contain the genetic information that is passed on to the offspring.

What are point mutations?

These describe the changes to a single nucleotide.

What are the types of point mutations?

Substitution

• Silent (amino acid remains the same)

• Missense (different amino acid)

• Nonsense (introduces a premature stop codon, creating a termination sequence)

Frameshift Mutation

• Insertion (nucleotide added to the sequence)

• Deletion (nucleotide removed from the sequence)

What are block mutations?

Involve changes to larger sections of DNA, potentially causing significant changes

When do block mutations usually occur?

During the process of meiosis

Define aneuploidy

when an individual has either one extra or one too few chromosomes

Define polyploidy

when an individual has more than two sets of chromosomes

Define environmental selection pressures, and provide examples

factors within the environment that influence the survivability of a species.

Examples include predation, disease, competition, and climate change

What is natural selection?

Organisms more suited to a particular environment are considered to have high genetic fitness due to the presence of their advantageous phenotypes

Overtime, because the fitter organisms have selective advantage they survive increasing the advantageous allele frequency in future populations

State the four conditions of Natural Selection

1. Variation

2. Selective pressure

3. Selective advantageous

4. Heritability

*discuss all four when explaining natural selection

What occurs at Variation?

Individuals in population vary genetically, which leads to phenotypic differences

What occurs at Selective Pressure?

An environmental selection pressure that impacts the survivability of organisms within a population and their ability to reproduce

What occurs at Selective advantageous?

Individuals with phenotypes that are fitter or more advantageous under the environmental selection pressure are given a selective advantage, allowing them to survive and reproduce

What occurs at Heritability?

The advantageous trait must be heritable, allowing it to be passed on from the parents ot their offspring. Therefore, over time, the frequency of the advantageous allele will increase

Define genetic variation

Differences in DNA sequences between individuals of the same species, leading to diverse traits/differences - this results from mutations, geneflow, sexual reproduction

How do selective pressure affect genetic diversity?

Selective pressures drive adaptations, and if a positive response is created, the frequency of advantageous traits will increase, at the expense of other disadvantages ones.

High genetic diversity increases the chance of possessing favourable alleles, aiding the species in surviving selection pressures.

Low genetic diversity exposes them to extinction due to the inability to adapt.

Define evolution

the change in genetic makeup of a population successive generations

define genetic drift

in response to random events, allele frequencies can change drastically and affect a population’s overall genetic diversity

What is the bottleneck effect?

• When a large portion of a population is wiped out by a random event (natural disaster)

• This decreases the population size, impacting allele frequencies - lower genetic diversity

What is the Founder effect?

• when a smal, unrepresentative sample of individuals seperate from the larger population, colonising in a new region

• The new populations genetic diversity is low

How does genetic drift reduce genetic diversity?

Through the random removal of alleles from the gene pool

It also increases the risk of inbreeding and lowers the adaptative potential

• Bottleneck reduces through random events

• Founder reduces through the establishment of a new population with a small un-representative sample

Define gene flow

The movement of alleles between different populations (either through migration or inbreeding)

Define immigration

When individuals enter a population, adding their alleles to the gene pool

Define emigration

Individuals exit a population, removing their alleles

Define a species

A group of individuals who are able to breed with eachother and produce viable offspring

Define speciation

The process by which populations genetically diverge until they become different species

→ this occurs when enough genetic differences have developed due to mutations, natural selection, gene flow and genetic drift

What are isolating mechanisms?

The pre-reproductive and post-reproductive mechanisms that prevent different species from interbreeding to produce fertile/viable offspring

What are the types of pre reproductive mechanisms that isolate populations causing speciation?

• geographical

• ecological

• temporal

• behavioural

• structural

What are the types of post-reproductive mechanisms that isolate populations causing speciation?

• gamete mortality

• zygote mortality

• hybrid sterility

Define allopatric speciation

involves the formation of new species as a result of a geographical barrier

How do geographical barriers cause the formation of new species?

A geographical barrier prevents gene flow, with different selection pressures causing genetic differences to develop until the two populations can no longer interbred

What is sympatric speciation?

Doesn’t rely on geographical barriers to prevent gene flow, it occurs within populations sharing the same locations where different selection pressures act on different phenotypes causing new species to develop.

Define selective breeding

When the selection pressure is human-induced, and there is a desired trait that humans are selecting for (or removing from the populations)

What are the requirements for selective breeding?

Variation: natural phenotypic variation within the population

Selection Pressures: the favourable trait is selected by humans, who they pressure and establish a breeding population with the trait-genetically controlled

Heritability: as the favourable trait is heritable, it will increase in allele frequency due to repeated selection reinforcements.

What is the main type of selective breeding, and the others?

Main: selecting for a trait you want

Others: selecting against the trait you want + selecting against the trait you don’t want