Genetic diversity,adaptation and types of selection Flashcards
What is genetic diversity
Genetic diversity is described as the total number of different alleles in a population.
What is a population
A group of individuals of the same species that live in the same place and can interbreed.
When is genetic diversity reduced
When a species has fewer different alleles.
Why is genetic diversity important to a species survival
- The greater the genetic diversity, the more likely it is that some individuals will survive an environmental change.
- This is because genetic diversity means that there is a wider range of alleles and therefore wider range of characteristics.
- The more characteristics there are, the higher the probability that an individual will have one that suits it to an environmental change and be able to survive and reproduce.
Summarise how natural selection/evolution works
Not all individuals survive to reproduce. The individuals that do are likely to have characteristics that better suit them to their environment and so have allowed them to survive. These characteristics will be passed onto the offspring- so evolution and adaptation occurs.
Describe how natural selection and reproductive success affects allele frequency in populations
- Within any population of a species there will be a gene pool containing a wide variety of alleles
- random mutation of alleles within this pool may result in a new allele of a gene which in most cases will be harmful.
- In certain environments, however, the new allele of a gene may give its possessor an advantage over other individuals in the population.
- These individuals are better adapted so are more likely to survive in their competition with others.
- These individuals are more likely to obtain the available resources and so grow more rapidly and live longer. As a result, they will have a better chance at breeding.
- only those individuals that reproduce successfully will pass their alleles on to the next generation.
- therefore the new, advantageous allele is more likely to be passed onto the next generation.
- over many generations the frequency of the ‘advantageous’ allele will increase and the others will decrease.
What are the two key types of selection
Directional selection and stabilising selection
Describe simply what directional selection is
Selection that favours individuals that vary in one direction from the mean of the population. It changes the characteristics of a population.
Describe simply what stabilising selection is
Selection that favours average individuals. It preserves the characteristics of a population.
What is selection
The process by which organisms that are better adapted to their environment tend to survive and breed, whereas those less adapted tend not to.
Which type of characteristics are more influenced by the environment
- Characteristics that are influenced by more than one gene (polygenes) are more influenced by the environment than ones determined by a single gene.
- Most characteristics are influenced by more than one gene.
What is a normal distribution curve
A graph that shows the variation in individuals of a population about a mean.
What are phenotypes
The observable physical and biochemical characteristics of an organism.
Describe directional selection and the affect this has on normal distribution curves
- If the environmental conditions change, the phenotypes that are best suited to the conditions are likely to survive.
- Some individuals, which fall to either the left or right of the mean, will possess a phenotype more suited to new conditions and are more likely to survive and reproduce.
- They will therefore contribute more offspring to the next generation than other individuals.
- Over time, the mean will move in the direction of these individuals and the position of the curve will shift (to either the right or left)
- Directional selection therefore results in phenotypes at one extreme of the population being selected for and those at the other extreme being selected against.
Describe stabilising selection and the affect this has on normal distribution curves
- if environmental conditions remain stable, it is individuals with phenotypes closest to the mean that are favoured.
- These individuals are more likely to pass their alleles onto the next generation.
-Those individuals with phenotypes at the extremes are less likely to pass on their alleles. - Stabilising selection tends to eliminate phenotypes at the extremes and results in phenotypes near the mean being selected for and those at BOTH extremes being selected against.
- This means the normal distribution curve stays roughly in the same position around the ideal mean.
