Natural selection and genetic modification revision notes

What is Genetic Engineering?

Genetic engineering is the deliberate modification of an organism's genome using biotechnology. This involves directly altering the DNA to change the characteristics of an organism. The primary goal is usually to introduce new, beneficial traits or to remove undesirable ones. This process differs from traditional selective breeding, which relies on natural reproduction and selection over many generations.

How Genetic Engineering Works

The basic steps include identifying a gene that codes for a desired characteristic, isolating this gene from the donor organism's DNA, and then inserting it into the DNA of the recipient organism, often using vectors like plasmids or viruses. Once integrated, the recipient organism (now a Genetically Modified Organism, or GMO) can express the new trait. Examples include inserting insulin-producing genes into bacteria for medical use, or genes for herbicide resistance into crop plants.

Applications and Ethical Considerations

Applications of genetic engineering are diverse, including producing pharmaceutical proteins (e.g., insulin), improving crop yields and pest resistance in agriculture, and developing disease-resistant animals. However, this technology also presents ethical debates. Concerns include the potential for unforeseen effects on ecosystems, the safety of consuming genetically modified foods, and questions about the 'naturalness' of altering an organism's fundamental genetic code. Regulations exist to manage these concerns.

From Five Kingdoms to Three Domains

The five kingdoms grouped organisms largely by appearance or nutrition, putting all prokaryotes into Monera. This approach missed deeper evolutionary differences that are not visible.

Role of Genetic Analysis

Modern methods, especially sequencing rRNA genes, showed profound genetic differences within prokaryotes. Instead of being one group, prokaryotes split into Bacteria and Archaea, each genetically distinct, resulting in the new three domains model.

What is the Pentadactyl Limb?

The pentadactyl limb is a five-digit limb structure found in many vertebrates. It is characterised by a consistent bone arrangement: one long bone (e.g., humerus), followed by two bones (e.g., radius and ulna), then a collection of smaller wrist/ankle bones (carpals/tarsals), leading to palm/foot bones (metacarpals/metatarsals), and finally the digits (phalanges).

Evidence for Evolution

The presence of the pentadactyl limb in diverse species like humans, bats, whales, and birds, despite their very different lifestyles and functions, serves as strong evidence for common ancestry. This structural similarity, known as homology, indicates that these organisms share a common evolutionary origin, with the limb structure modified over time through natural selection to suit specific environmental demands. This pattern suggests divergent evolution from a common ancestral form.

Examples of Diversification

While the underlying bone structure remains similar, the pentadactyl limb has adapted for various functions. For example, a human arm is adapted for grasping and manipulation, a bat's wing for flight, a whale's flipper for swimming, and a horse's leg for running. These adaptations demonstrate a common blueprint being modified, rather than entirely new structures evolving independently, supporting the idea of a shared ancestor.

What is Selective Breeding?

Selective breeding (also known as artificial selection) is the process by which humans choose individual organisms with desirable characteristics and breed them together. The offspring that inherit these desired traits are then chosen for further breeding, repeating the process over several generations. This aims to enhance specific traits within a population.

Process of Selective Breeding

The steps typically involve: 1. Identifying a desirable trait. 2. Choosing parents that exhibit this trait strongly. 3. Breeding these parents. 4. Selecting offspring that show the trait most strongly. 5. Repeating the process over many generations to intensify the trait. This leads to cumulative changes in the population.

Impact on Food Plants

Selective breeding has profoundly impacted food plants. Examples include developing wheat varieties with higher grain yield, rice with improved nutritional content, and fruits with increased size or sweeter taste. It also helps cultivate crops resistant to common pests and diseases, ensuring more reliable food production and reducing reliance on chemical treatments. This has been crucial for feeding a growing global population.

Impact on Domesticated Animals

For domesticated animals, selective breeding has created breeds optimized for various human needs. Dairy cows are bred for high milk production, chickens for rapid growth or egg-laying capacity, and sheep for wool quality or meat yield. Dogs have been selectively bred for specific temperaments and abilities, such as herding, guarding, or companionship. These changes often make the animals highly specialized for their purpose.

Advantages and Disadvantages

Advantages include increased food production, improved quality of products, and development of disease-resistant strains. Disadvantages can arise from reduced genetic diversity, making populations more vulnerable to new diseases or environmental changes. Inbreeding, which can occur, may also lead to hereditary disorders being more common within a population due to limited gene pool.