Biology Topic 4 [3.4.4 onwards]: variation and relationships between species

define genetic diveristy

the number of different alleles of genes in a population

how does genetic diversity affect natural selection?

genetic diversity is a factor that enables natural selection to occur

what is natural selection?

• the process where organisms with advantageous traits for their environment are more likely to survive and reproduce, passing on those traits to their offspring

• this results in species that are better adapted to their environment. These adaptations may be anatomical, physiological or behavioural

what is evolution?

The gradual change in a population's characteristics over time due to natural selection acting on genetic variations. 

outline the process of natural selection

• random mutation results in new alleles of a gene

• in certain environments, this allele is advantageous to the possessor, so the individual has increased reproductive success

• individuals without the allele are selected against by the selection pressure, so are outcompeted by mutated individuals

• mutated individuals pass the advantageous allele onto their offspring

• as a result, over many generations, the new allele increases in frequency in the population

what is directional selection?

• when the environment favours a particular extreme of a trait

• over time, the mean of the popular shifts in favour of that extreme

• e.g. when a population is bacteria is exposed to an antibiotic, bacteria that mutate and gain the allele for antibiotic resistance will reproduce and survive

• this leads to a gradual increase in the antibiotic resistance of the population

what is stabilising selection?

• when an environment favours the intermediate phenotype, and selects against the extremes.

• this typically occurs in a stable environment

• e.g. babies with low birth weights are prone to infection and have thermoregulation issues, whilst babies with high birth weights have issues during delivery.

• thus, babies with intermediate birth weights are selected for

what are anatomical adaptations?

• physical features of an organism that improve survival

• e.g. giraffes having long necks

what are physiological adaptations?

• changes in internal biochemical processes

• e.g. snakes producing venom

what are behavioural adaptations?

• patterns of behaviour that increase the chance of survival

• e.g. mating calls, migratory behaviour

how do we know if two organisms belong to the same species?

if they are able to interbreed and produce fertile offspring

what is courtship behaviour?

• sequence of actions carried out by an organisms to attract a mate of the same species and opposite sex

• necessary precursor to successful mating

why is courtship behaviour important?

• helps organisms to identify potential mates of the same species

• allows animals to assess the health of a prospective mate

• can lead to the formation of a bond pair

• helps synchronise mating behaviours (release of egg and sperm at the same time, increasing chances of fertilisation)

• indicates sexual maturity

what is a phylogenic classification system?

• arranges species into groups based on their evolutionary origins and relationships

• uses a hierarchy in which smaller groups are placed within larger groups, with no overlap. these groups are taxa (taxon: singular)

what is a taxon composed of?

domain > kingdom > phylum > class > order > family > genus > species

what is a binomial?

genus, species