3.4.4 genetic diversity and adaptation Flashcards
what is genetic diversity?
described as the total number of different alleles in a population
genetic diversity is reduced when a species has fewer different alleles
the greater the genetic diversity the more likely individuals in a population will survive an environmental change
how do differences between the reproductive success of individuals affect allele frequency in populations?
gene pool containing a wide variety of alleles
random mutations of alleles may result in a new allele of a gene, mostly harmful
however may be advantageous and lead to successful adaptation to environmental changes
what is selection?
process by which organisms that are better adapted to their environment survive and breed
different environmental conditions favour different characteristics
what is directional selection?
favours individuals that vary in one direction from the mean
changes the characteristics of the population
what is stabilising selection?
favours average individuals and preserves the characteristics of the population
describe selection
most characteristics are influenced by more than one genes (polygenic)
the effect of the environment on polygenes produces individuals in a population that vary about the mean
can be plotted on a graph
describe directional selection
occurs in populations exposed to change in environment
if environment changes, so will the phenotypes needed for survival
those with less common phenotypes, will be more likely to survive and reproduce
over many generations, the mean will move in the direction of these individuals
results in phenotype at one extreme of the population being selected for and the extreme being selected against
eg development of antibiotic resistance in bacteria
how is penicillin resistance directional selection?
random mutation of bacteria resulting in production of penicillinase
in the presence of penicillin, these mutants will have a competitive advantage and be more reproductively successful
over many generations and continued use of antibiotics, the mutant population will gradually replace the original population
frequency of alleles conferring antibiotic resistance will increase
what is stabilising selection?
occurs in populations which inhibit environments which remain reasonably constant
tends to eliminate extreme phenotypes so that the mean phenotype remains more or less constant from generation to generation
individuals with phenotype closest to the mean are favoured and more likely to pass alleles onto the next generation
what adaptations of natural selection are there?
- anatomical eg shorter ears and thicker fur in artic foxes compared to foxes in warmer climates
- physiological eg oxidising of fat rather than carbohydrate in kangaroo rats to produce additional water in a dry desert environment
- behavioural = autumn migration of swallows from the UK to Africa to avoid food shortages
