Biology (0610) Variation and Selection Revision Note

This document covers variation and selection for CAIE IGCSE Biology, focusing on how differences arise within species and how they influence survival. Variation is explained as differences between individuals, caused by genetic factors, environmental influences, or both. Two types are highlighted: continuous variation (a range of phenotypes like body mass or height) and discontinuous variation (distinct categories like blood groups or seed colour). Mutations are described as genetic changes that create new alleles, with meiosis, random fertilisation, and mating also contributing to diversity. Ionising radiation and chemicals are noted as mutagenic agents. The section on adaptive features describes structural traits that enhance survival: xerophytes adapted to dry environments with deep roots, spines, and rolled leaves; and hydrophytes adapted to aquatic environments with divided leaves, air spaces (aerenchyma), and stomata on the upper surface. Selection is explained through natural and artificial processes. Natural selection ensures that individuals with advantageous traits survive and reproduce, passing their genes on, illustrated with antibiotic-resistant bacteria. Artificial selection is directed by humans, breeding organisms with desirable traits such as high milk yield in cows, stronger crops, or specific dog breeds. This guide provides a complete overview of adaptation, evolution, and selective breeding.