natural selection Flashcards
explain what Darwin deduced about natural selection
-Not all individuals are as likely to reproduce as each other. Individuals that have a random mutation of an allele which increase their chance of survival are more likely to survive and reproduce, therefore passing this gene on. As a result, the ones without the gene die out and the frequency of this allele increases in the population over a number of generations. This eventually leads to evolution.
in what 3 ways does natural selection lead to organisms being better adapted to their environment?
-BEHAVIOURAL: the way an organism acts (eg mating or migration)
-PHYSIOLOGICAL: the processes which occur inside the organisms body
-ANATOMICAL- the structural features or an organisms body
what factors apart from mutations can affect allele frequencies in a population?
The founder effect, genetic drift, the bottleneck effect
explain the founder effect
the founder effect occurs when only a small number of individuals from a large parent population start a new population. As this new pop is only made up of a few individuals from the OG pop, not all of the gene pool is present. As a result, the changes in allele frequency may occur in a different direction and this is completely due to chance.
explain genetic drift
When a population is significantly small, chance can affect which alleles get passed on to the next generation. Over time, some alleles can be lost or favoured. when there is a gradual change in allele frequencies in a small population due to chance and not natural selection, this is genetic drift
explain the bottleneck effect
Occurs when a previously large population suffers a fall in numbers due to an unselective event such as an environmental change (eg flood). This reduces the genetic diversity in the population as alleles are lost or over-represented. This means that it is less likely that the population can adapt to changes in the environment.
what are selection pressures?
environmental factors that affect the chance of survival of an organism
what can selection pressures affect?
allele frequencies
what are the 2 types of selection?
stabilising and directional
what is stabilising selection?
natural selection that keeps allele frequencies relatively constant over generations. It favours the average phenotype and is against extreme phenotypes and preserves the populations characteristics. Keeps things the same unless there’s a change in the environment.
what is directional selection?
natural selection that produces a gradual change in allele frequencies over several generations. One extreme phenotype is selected over another. This usually happens when there is a change in the environment or a new advantageous allele has appeared in the population.
define the term evolution
the change in adaptive features of a population over time as a result of natural selection
