selection Flashcards
3 types of selection
- stabilising
- directional
- disruptive
define selection pressures
environmental factors that limit the population of a species
give 3 selection pressures
predation
disease
competition
define evolution
change in the allele frequencies in a population
define allele frequency
number of times an allele occurs in a population
why do some organisms have a high reproductive rate
ensure large populations survive to breed due to lots of predation
how do species with low reproductive rates ensure survival of the species
high levels of parental care and therefore lower death rates
explain the process of stabilising selection
selecting for optimum and against extreme phenotype
no/ reduce evolutionary change
no environmental change (stable environment/environmental conditions are constant)
preserves average phenotype by favouring average individuals
explain the process of directional selection
allele frequency changes (changes phenotype of population in 1 direction)
evolution occurs
driven by an environmental change
selecting against 1 extreme
explain the process of disruptive selection
selecting for extreme of a population and against intermediate (mean)
great evolutionary change - speciation
why is allele frequency of subsequent generation different from the previous
organisms better adapted to their environment survive and pass on favourable alleles
explain why it is an advantage for organisms well adapted to their environment to not produce offspring identical to themselves
environmental conditions change over time and having a wide range of alleles therefore phenotypes in the population means that some will have the combination of genes needed to survive
explain the process of natural selection
there is variation within a population
individuals with phenotypes providing a selective advantage are more likely to survive
these reproduce and pass on genes to next generation
increase in frequency of selected allele in the gene pool
explain how evolutionary change over a long period of time has resulted in a great diversity of species
organisms adapt to their environment
many different environments results in many different adaptations and therefore genetic diversity
Explain the role of variation in natural selection
Variation is important in natural selection as environmental conditions change over time.
A wide range of genotypes and therefore phenotypes in a population will mean some have the characteristics to survive in most new sets of circumstances
