Evolution Flashcards
Evolution definition
changes in the heritable characteristics of organisms over generations
natural selection
organisms that are better adapted to their environment survive, reproduce, and pass on their advantageous alleles, causing advantageous characteristics to increase in frequency within a population
variation
small differences in DNA base sequences between individual organisms within a population
essential stages to talk about in regards to natural selection
Variation is present in a population
Selection pressures affect a population
Those with advantageous alleles are more likely to survive and reproduce
Advantageous alleles are passed to offspring
Advantageous alleles become more frequent in the population
speciation
development of new species from pre-existing species over time
what needs to happen from speciation to occur
two populations of the same species must be isolated from each other
When this happens, there can no longer be an exchange of genes between the two populations
two reasons why isolations of populations may occur
Geographical isolation
This leads to a type of speciation known as allopatric speciation
Random mutations that prevent them from interbreeding with each other
This leads to a type of speciation known as sympatric speciation
when does allopatric speciation occur
when populations of a species become separated from each other by geographical barriers
This creates two populations of the same species between which no gene flow is taking place
how does isolation occur in sympatric speciation
random changes in the alleles and therefore phenotypes of some individuals in a population prevent them from successfully breeding with other individuals in the population
Three examples of phenotype changes that lead to isolation
Seasonal changes
Some individuals in a population may develop different mating or flowering seasons to the rest of the population, i.e their reproductive timings no longer match up
Mechanical changes
Some individuals in a population may develop changes in their genitalia that prevent them from mating successfully with individuals of the opposite sex, i.e. their reproductive body parts no longer match up
Behavioural changes
Some individuals in a population may develop changes in their courtship behaviours meaning they can no longer attract individuals of the opposite sex for mating, i.e. their methods of attracting a mate are no longer effective
evidence for evolution
The fossil record
We can tell from fossils that organisms have changed significantly over millions of years
Fossils can show evidence for transitional species, showing how one species could evolve into another
Analysis of biological molecules such as DNA and proteins show similarities between species that indicate evolution of species from a common ancestor
If a bacterial infection is treated with an antibiotic, a bacterial individual with a random mutation for antibiotic resistance is likely to survive and reproduce
The antibiotic in this situation acts as a selection pressure
evidence from gene sequences for evolution
Comparing the sequences of equivalent genes in different species can show
The base sequences of some genes are very similar across many different
species; this indicates common ancestry
The level of similarity between base sequences of equivalent genes can give a measure of how long ago two species diverged from each other during speciation
