How It Works: How Variation Arises
Part of Variation — GCSE Biology
This how it works covers How It Works: How Variation Arises within Variation for GCSE Biology. Genetic and environmental variation in organisms It is section 4 of 10 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 4 of 10
Practice
25 questions
Recall
20 flashcards
How It Works: How Variation Arises
Variation between individuals arises from three main sources: genetics, environment, and mutations. Sexual reproduction is the primary mechanism for generating genetic variation. During meiosis, chromosomes are shuffled — homologous chromosomes pair up and exchange segments in a process called crossing over, and then separate randomly into gametes. This means each gamete contains a unique combination of alleles. When two gametes from different parents fuse at fertilisation, the resulting offspring has a novel combination of alleles from four grandparents, ensuring no two individuals (except identical twins) are genetically identical.
Mutations are spontaneous, random changes in DNA base sequence. Most mutations have no effect on the organism (they occur in non-coding DNA or are repaired by cellular machinery). Some mutations are harmful — they produce non-functional proteins. Rarely, a mutation is beneficial and may be selected for by natural selection. Mutations are the ultimate source of all new genetic variation in a population; without them, only existing allele combinations would be possible.
Environmental variation arises because development and phenotype are influenced by the conditions in which an organism lives. Identical twins share the same genome, but differences in diet, exercise, disease exposure, and lifestyle mean they can have measurably different heights, weights, and even facial features as adults.