Variation and evolution

What factors produce variation between individuals

Genetic and environmental factors

4 types of variation

continuous, discontinuous, heritable, inheritable

discontinuous variation

variation that is categorised, can only appear in discrete values, is influenced by 1/2 genes (monogenic) and environmental factors have little effect

Continuous variation

variation that cannot be categorised, produces a continuous range in which a characteristic can take any value, influenced by multiple genes (polygenic) and often significantly affected by environmental factors

Heritable variation

the genetic differences between individuals

Non-heritable variation

acquired differences in the phenotypes of individuals that cannot be inherited

Evolution

the change in allele frequencies in a gene pool of a population over time

How does natural selection cause a change in allele frequencies over generations

organisms with advantageous characteristics are more likely to survive and pass their favourable alleles to offspring. Frequency of unfavourable alleles decreases/are no longer present

Selection pressures

environmental factors that drive evolution by natural selection. They limit population sizes and can change the frequency of alleles in a population

Examples of selection pressures

predation, disease, competition, environmental conditions

How can allele frequencies be expressed

as a percentage or proportion of the total number of all alleles for that gene

2 types of competition

interspecific - different species, intraspecific - same species

Gene pool

all the different alleles of all the individuals in a population at one time

Genetic drift

variations in allele frequencies in small populations due to chance (rather than as a result of selection pressures)

Founder effect

when a small number of individuals become isolated, forming a new population with a limited gene pool. Allele frequencies aren’t reflective of the original population.

Hardy-Weinberg principle

a model that allows the estimation of the frequency of alleles in a population, as well as whether allele frequency is changing over time.