What is the biological importance of variation and what causes it?
Paragraph 1 — Mutation
Biggest source of new alleles.
Mutation can arise from:
substitution
insertion
deletion
chromosome mutation
Causes:
errors in DNA replication
mutagens (radiation / chemicals)
Importance as cause:
Creates new alleles.
Essay point:
Mutation is a major cause of genetic variation because it introduces new alleles into a population.
Paragraph 2 — Meiosis
Huge paragraph.
Variation caused by:
crossing over
independent assortment
During meiosis:
homologous chromosomes exchange alleles
chromosomes segregate randomly
Importance:
Produces genetically unique gametes.
Essay point:
Meiosis generates variation by producing gametes with different combinations of alleles.
Paragraph 3 — Environmental variation
Not all variation is genetic.
Examples:
diet affects mass
sunlight affects skin pigmentation
training affects muscle mass
This produces continuous variation.
Importance:
Phenotype depends on environment too.
Paragraph 4 — Natural selection and evolution
This is the most important paragraph.
Natural selection depends on variation.
Process:
Variation exists
Some phenotypes have selective advantage
Survivors reproduce more
Allele frequency changes
Without variation:
no selection
no evolution
Essay point:
Variation is essential for natural selection because selection cannot occur if all individuals are genetically identical.
Paragraph 5— Disease resistance
Variation improves population survival.
Examples:
immune receptor diversity
antibody diversity
Importance:
Some individuals better resist pathogens.
This reduces risk of entire population being wiped out.
Paragraph 6 — Agriculture / artificial selection
Good synoptic paragraph.
Humans exploit variation for:
selective breeding
crop improvement
disease resistance
Examples:
larger yield
drought resistance
milk production
Variation enables artificial selection.