Variation is the measurable difference between individuals of a species, produced by mutation, sexual recombination, polygenes, and environmental influences over development.
Variation means members of a species differ in traits, and it is a defining feature of life because populations are not exact copies.
Differences can arise from mutation, recombination, gene flow and environmental effects. Heritable variation supplies material for evolution; non-heritable differences can still affect an individual without changing the next generation’s gene pool.
Separate sources of variation:
Two genetically similar plants can grow to different heights in different light, while a DNA mutation can create a heritable difference in pigment.
Variation is not automatically an adaptation; it must be heritable and affect reproductive success to drive selection.
This objective is assessed through structured response, commonly using State.
State
Build the answer around this relationship: Variation occurs between individuals within every species.
Describing visible differences without naming a genetic or reproductive cause of variation.
Representative question
State, giving a reason, the type of variation shown by shell length.
a. (it shows) continuous variation;
b. as there are many intermediate lengths between the two extremes / normally distributed
OR
no distinct categories
OR
all shell lengths are possible (between the extremes);
b. bell shape curve is not sufficient.
2
Marking guidance:
max
For SL, A3.1 is really one evidence map. Variation explains why individuals differ. Morphology and binomial nomenclature help group and name organisms. The biological species concept uses interbreeding and fertile offspring, but boundaries can be difficult during gradual speciation. Chromosomes and karyograms add cellular evidence. Genomes, SNPs, genome size, and whole genome sequencing add molecular evidence. The skill is choosing the right evidence for the question.