3.4.4 - genetic diversity and adaptation Flashcards
what is genetic diversity?
the number of different alleles of genes in a population
what does genetic diversity do?
enable natural selection to occur
what are the principles of natural selection?
- random mutations result in new alleles of a gene which causes variation in a gene pool
- many mutations are harmful but, in certain environments, the new allele of a gene might benefit its possessor, leading to increased reproductive success
- the advantageous allele is inherited by members of the next generation
- over many generations, the new allele increases in frequency in the population
what does natural selection result in?
species which are better adapted to their environment - the adaptions may be anatomical, behavioural or physiological
what are adaptations?
traits that have been selected for because they help increase an organisms’ chance of survival and reproduction
what are anatomical adaptations?
physical structures that have evolved to increase the chance of survival eg. giraffes having long necks so they can access food in the top levels of trees which other species can’t reach
what are physiological adaptations?
processes within the body that have evolved to increase the chance of survival eg. snakes producing venom to protect them from potential predators and which can be used to capture prey
what are behavioural adaptations?
actions that have evolved to increase the chance of survival eg. cheetahs evolving to ‘stalk’ (silently creeping before chasing) their prey to increase the chance they will successfully catch it
what are selection pressures?
environmental factors which affect the chance of survival of an organism
what are two types of natural selection?
directional selection and stabilising selection
what is stabilising selection?
natural selection which favours an average phenotype, so allele frequencies remain relatively constant over generations
where does stabilising selection occur?
in environments which don’t change
what is an example of stabilising selection?
human birth weights - very high and very low weights are selected against, leading to the maintenance of intermediate birth weights
what is directional selection?
natural selection which favours one extreme phenotype, so it produces a gradual change in allele frequencies over several generations
where does directional selection occur?
in environments which have experienced a change - this could be a new selection pressure or new advantageous allele
what is an example of directional selection?
antibiotic resistance in bacteria - only bacteria which are resistant to the antibiotics are selected for
