Evolution may lead to speciation (A-level only) Flashcards
Genetic variation
There is huge variation between individuals in the same species.
E.g. A golden retriever looks completely different from a pug but they are both part of the species Canis familiaris.
This variation is caused by differences in the genetic code.
This is called genetic variation.
Genetic variation happens when individuals in the same species have different alleles.
Alleles are different versions of the same gene.
Environmental variation
Environmental factors can also contribute to phenotypic variation.
The genotype of an individual interacts with the environment.
E.g. If an individual has the alleles for being tall but is fed a nutrient-poor diet, they will not grow as tall as an individual with the same alleles and a more nutrient-rich diet.
Causes of genetic variation
Mutation
Recombination
Independent segregation
Random fertilisation
Mutation
Mutation is the main source of genetic variation.
Mutations are changes in the base sequence.
Changes may cause the structure of proteins encoded by DNA to be altered.
Some mutations are harmful (e.g. the mutation that causes disease), some are beneficial and some have no effect on survival.
Recombination
Meiosis is the process that produces haploid gametes from diploid cells.
During meiosis, the genes on homologous chromosomes are reshuffled through a process called recombination or crossing over.
Recombination produces new combinations of genes.
This increases genetic variation.
Independent segregation
Meiosis also involves the independent segregation of chromosomes into haploid cells.
The chromosomes in a pair of homologous chromosomes are randomly separated and this creates genetic variation.
Random fertilisation
During sexual reproduction, the gametes of two unrelated individuals are fused to produce a diploid individual.
This process is called random fertilisation.
Random fertilisation produces genetic variation because pairs of chromosomes from two separate individuals are combined.
Whether an individual is capable of surviving or not is influenced by the following factors:
Predation
Disease
Competition
Predation
Predation can decrease the probability of survival.
If an individual is exposed to high predation, they are more likely to be eaten by a predator.
If an individual is better at avoiding predators, they are more likely to survive and reproduce.
The genes that allow an individual to avoid predation are more likely to be passed onto offspring.
Disease
Disease can decrease the probability of survival.
If an individual is better at combatting disease or avoiding infection, they are more likely to survive and reproduce.
The genes that allow an individual to avoid disease are more likely to be passed onto offspring.
Competition
Competition can decrease the probability of survival.
Competition can exist between species (interspecific) or within species (intraspecific).
If an individual is better at outcompeting other individuals, they are more likely to survive and reproduce.
The genes that allow an individual to outcompete are more likely to be passed onto offspring.
Natural selection
Natural selection is the process where the frequency of alleles in a population changes over time.
Natural selection is a process that gives rise to evolution.
Selective advantage
Genetic variation exists between individuals in a population.
Some individuals will be more likely to survive (e.g. by being better at fighting disease) than others.
Individuals that are better at surviving than others have a selective advantage.
Producing offspring
Individuals with a selective advantage are more likely to survive to reproduce than others.
This means that the genes of an individual with a selective advantage are more likely to be passed onto offspring than the genes of an individual without a selective advantage.
Increasing allele frequencies
Individuals with a selective advantage are more likely to pass on their beneficial alleles than other individuals.
The next generation is more likely to have alleles that provide a selective advantage than alleles that do not.
This generation is also more likely to survive to reproduce and pass on their genes.
This causes the alleles that provide a selective advantage to increase in frequency in the population.