- a mechanism in which physically, physiologically, environmentally and generally adapted organisms survive and reproduce
- organisms best suited in the environment survive and reproduce to pass on their allele in the net generation.
- organisms that are not suited in the environment do not survive and reproduce hence they don’t continue to exist (extinction).
- environmental factors may result in other organism best suited for surviving and other die
- Such environmental factors exert selection pressure
Types of selection
- Artificial Selection
- Natural Selection
How mutation can affect phenotype.
- gene) example ; (sickle cell / PKU )
- change in gene / DNA / base change ;
- different amino acid ;
- different polypeptide / different protein / non-functional protein ;
- (chromosome) example ; (Down’s, Turner’s syndromes)
- structural changes in chromosomes ;
- change in number of chromosomes ;
- change in sets of chromosomes / ref. polyploidy ;
How the environment may affect the phenotype of an organism.
- phenotypic variation results from interaction of genotype and environment
- environment may limit expression of gene(s) ;
- e.g. for size / mass / height ;
- because, food / nutrients / ion, missing / malnutrition ;
- named, nutrient / ion / mineral, missing ;
- environment may, trigger / switch on, gene ;
- ref. low temperature and change in animal colour ;
- ref. high temperature and, curled wing in Drosophila / gender in crocodiles ;
- ref. UV light and melanin production ;
- ref. wavelength of light and, flowering / germination / fruit colour ;
- other named trigger plus example ;
- environment effect usually greater on polygenes ;
- environment may induce mutation affecting phenotype ;