Explain why gene duplication is evolutionarily important.

Genetic diversity is the cornerstone of a species' survival and adaptation. Through gene duplication, the repertoire of genes within an organism's genome is expanded. This process provides the raw material for evolution, as it creates genetic variations that can lead to a variety of new physical features and abilities. Gene duplication contributes to genetic diversity in several ways: it increases the number of genes available for evolutionary modification and allows for backup copies to safeguard against deleterious mutations in essential genes.

Furthermore, duplicated genes can diverge over time, resulting in novel functions or enhancements to existing ones. Such diversity within the genome is vital as it offers a broader set of options from which natural selection can 'choose' in response to changing environmental pressures. This increased genetic toolkit equips species with the means to face an ever-changing landscape of ecological challenges.

The evolutionary significance of gene duplication cannot be overstated. It acts as a principal mechanism for introducing new genetic material into a population, which is essential for the long-term survival and evolution of organisms. When a gene is duplicated, it lifts the constraint of having to maintain its original function, thereby providing freedom for one copy to take on different roles or become specialized. These innovations can lead to increased fitness, the development of complex gene families, and the emergence of new species.

Gene duplication events have been pivotal in the development of vital biological systems, such as the complex immune defenses found in vertebrates or the sophisticated visual systems in primates. By understanding how gene duplication shapes the tree of life, we gain insight into the processes that have led to the vast array of organisms and adaptations we see today.

Gene duplication can occur through a variety of mechanisms that differ in their frequency and impact on an organism’s genome. The three main mechanisms are:

• Unequal crossing over during meiosis involves the anomalous recombination of genetic material between homologous chromosomes resulting in one chromosome with a duplicated gene and a potential loss in another.
• Retrotransposition involves a gene being copied from an RNA molecule back into DNA and inserted into the genome at a new location.
• Whole-genome duplication is when an error in cell division leads to a doubling of the entire genome. Such events can trigger large-scale evolutionary changes and speciation.

Each of these mechanisms adds a different facet to the evolution of genomes and can have diverse outcomes on the organism and its descendants.

Neofunctionalization is a crucial evolutionary process that follows gene duplication. It describes the event where a duplicated gene acquires mutations that confer a novel function not present in the ancestral gene. This newly acquired function helps the organism exploit new ecological niches or adapt to environmental changes. The classic model of neofunctionalization suggests that, after gene duplication, one copy retains the original function, while the other copy is free to mutate and potentially develop new functionality. This can lead to a beneficial function that will be favored by natural selection.

An example of neofunctionalization is the evolution of different hemoglobin proteins that support life at various oxygen levels and stages of development. This process contributes immensely to biodiversity by providing a pathway for the innovation of new protein functions and complex adaptations.