Genetic changes in a population over time Flashcards
Gene pool
Is the sum of alleles within a given population
Population
Refers to an interbreeding (viable and fertile offspring) group of organisms of the same species living in the same region at the same time.
Allele frequency in a population
Gene pools are described by the frequencies (proportions) of the alleles of each gene present. The frequency of an allele within the gene pool is referred to as the allele frequency
Environmental selection pressures
External agents which influence the ability for an individual, population or species to survive through natural selection.
- Biological agents: Disease, competition, sexual selection
- Chemical agents: pollutants in soil, pollutants in water, drugs
- Physical agents: climate change, food shortage, availability for shelter
Biological vs physical fitness
- Biological fitness considers reproductive success and the contribution of alleles to future generations and the gene pool.
- Physical fitness is linked with health and athletic ability.
Natural selection
- There is variation within the population’s gene pool.
- There is a struggle for all individuals in the gene pool to survive due to environmental selection pressures.
- Individuals that are better adapted to their environment are more likely to survive and reproduce, passing their alleles on to the next generation.
- The alleles that allow for survival will be inherited by subsequent generations and they can increase in frequency in the gene pool over time.There is variation within the population’s gene pool.
Genetic drift
Is the change in allele frequency overtime, caused by unpredictable random events. This means that alleles passed on or retained may not be representative of the initial population. Has a larger effect on a smaller population.
Bottleneck effect
When the size of a population is drastically reduced for at least one generation. The few survivors that reproduce may by chance be an unrepresentative sample of the gene pool of the original population. Often due to natural disaster, disease, human activity of destruction
Founder effect
Occurs when a new colony is started by a few members from a larger population. Often has reduced genetic variation and unrepresentative samples of the original population
Gene flow
Gene flow is the movement of alleles between interbreeding populations or through immigaration or emigration. Interbreeding between population = genetic diversity, no interbreeding between population = genetic isolation
Emigration - exit a population
Immigration - come to a population
Mutation
Mutation = a permanent alteration in the DNA sequence of a gene that leads to the formation of new alleles.
Causes of mutations: can be spontaneous / induced by mutagens (agents that cause mutation)
Point mutations
single nitrogenous base change
- Silent mutations (does not result in a change in the amino acid)
- Nonsense mutations (results in a stop codon rather than codon for an amino acid)
- Missense mutations (change in one amino acid to another amino acid)
Frameshift mutations
Change that results in alteration to the reading frame as a result of an insertion or deletion of a base
- insertion or deletion
Chromosomal mutation
- Deletions - When a chromosome breaks in two places, losing the middle section, and the remaining sections rejoin.
- Inversion - When a chromosome breaks in two places, and middle piece turns around and joins up again - normal sequence of genes is reversed
- Translocation - When a piece of a chromosome breaks off and joins up with another chromosome
- Duplication - When a section of chromosome replicates (set of genes repeated, can be thousands repeats)
Populations with high genetic diversity
- Gene pool with a large number of alleles for each gene
- Diversity allows the population to be resilient to environmental changes - some individuals will be able to adapt to the changed conditions and survive.
- Tend to be large in size and have gene flow with other populations’ gene pools within its species.
→ From: Gene flow, mutations
Populations with low genetic diversity
- Decreases in the rate of interbreeding (reduce genetic diversity).
- This can limit the population’s ability to adapt to changing environmental conditions, and can make them vulnerable to becoming susceptible to disease and possible extinction.
- The bottleneck and founder effect play a significant role in lowering genetic diversity
- Generally smaller and do not have gene flow with other populations
→ From: Natural selection, genetic drift, bottleneck, (domesticated setting due to selective breeding) founder effect, inbreeding
Selective breeding programs
The deliberate manipulation of a species’ gene pool by selecting individuals with specific traits desirable to humans to breed (artificial selection)
Artificial selection can maintain features in a population that are economically important or aesthetically appealing but are disadvantageous in terms of survival and reproduction.
Populations with low diversity are more susceptible to being eliminated from diseases
Steps for selective breeding
- There is variation within the population’s gene pool.
- Humans select individuals with a desirable trait.
- These individuals breed (reproduce) and pass their alleles on to the next generation.
- The alleles that lead to the desired phenotype will be inherited by subsequent generations and they can increase in frequency in the gene pool over time.
Viral antigenic drift
When a point mutation alters a virus’s nucleic material, resulting in small changes to its antigens/ small and gradual changes in the genes encoding for viral surface antigens.
Viral antigenic shift
Occurs when two or more strains of a virus combine to form a new strain of the virus with antigens from each of the original strains/ sudden and significant change in the genes encoding for viral surface antigens.
Consequences of bacterial resistance
- With the number of bacteria with resistance to antibiotics rising globally, it is becoming more challenging to treat common infectious diseases
- Diseases which could once be treated with a dose of antibiotics can now be life-threatening to individuals with an antibiotic-resistant strain of infection because the bacteria can continue to reproduce in the body.
Challenges for treatment strategies and vaccination
- Objective to achieve herd immunity - may be select number of people that wont get vaccinated
- Risks and side effects of vaccines
- Don’t get boosters
- Refuse to comply with medical advice regarding isolating and when to get vaccinated etc..
