Natural selection and genetic modification Study Guide

Genetic engineering involves modifying an organism's DNA by inserting, deleting, or altering genes. It begins with isolating the desired gene and cutting it out using restriction enzymes, which recognise specific DNA sequences and create 'sticky ends' – short, single-stranded overhangs. A 'vector', such as a bacterial plasmid, is also cut with the same restriction enzyme, producing complementary sticky ends. The isolated gene is then mixed with the cut vector, and the complementary sticky ends anneal. An enzyme called DNA ligase forms phosphodiester bonds to permanently join the gene into the vector, creating recombinant DNA. This recombinant DNA is then introduced into a host cell (often bacteria), which can then express the new gene, producing the desired protein or trait.

Selective breeding, also known as artificial selection, is a process where humans intentionally choose organisms with desirable traits to reproduce, aiming to enhance those traits in subsequent generations. This process has been widely applied to both food plants and domesticated animals over thousands of years. For food plants, selective breeding has led to the development of varieties with higher yields, improved resistance to diseases and pests, better nutritional content, and enhanced growth rates. Examples include larger, sweeter fruits or grains that are easier to harvest. In domesticated animals, selective breeding has resulted in breeds with increased meat or milk production, improved wool quality, specific adaptations for draft work, or more docile temperaments. The key impact is that it allows for the acceleration of evolutionary changes to benefit human needs, by selecting for traits that would not necessarily be favoured by natural selection in the wild. While beneficial for humans, it can lead to reduced genetic diversity within species, making them more vulnerable to new diseases or environmental changes.