Rucete ✏ Campbell Biology In a Nutshell
Unit 3 GENETICS — Concept 21.5 Duplication, Rearrangement, and Mutation of DNA Contribute to Genome Evolution
Genomes evolve through duplication, rearrangement, and mutation of DNA sequences, processes that can lead to the creation of new genes, altered gene functions, and increased genome complexity.
Duplication of Entire Chromosome Sets (Polyploidy)
Polyploidy occurs when organisms inherit extra sets of chromosomes due to errors in meiosis.
While often lethal, polyploidy occasionally provides a genetic advantage, allowing mutations to accumulate and evolve new gene functions without compromising essential functions.
Polyploidy is rare in animals but common in plants, contributing significantly to plant speciation (approximately 80% of plant species show ancestral polyploidy).
Alterations of Chromosome Structure
Structural changes such as chromosome fusions, duplications, deletions, and rearrangements contribute to genome evolution.
Example: Human chromosome 2 resulted from a fusion event between two ancestral chromosomes (seen separately in chimpanzees), evidenced by telomere and centromere sequences.
Comparative genomic analysis (e.g., human and mouse genomes) reveals chromosomal rearrangements, duplications, and inversions that contribute to species diversity and speciation.
Frequent chromosomal rearrangements at certain "hot spots" correlate with genetic diseases.
Duplication and Divergence of Gene-Sized Regions of DNA
Unequal crossing over during meiosis can duplicate or delete gene-sized regions, often involving misalignment due to transposable elements.
Gene duplication provides raw material for evolutionary change:
Extra gene copies may accumulate mutations without losing essential functions.
Resulting divergent genes can evolve new functions, creating multigene families.
Example: The human globin gene families evolved from duplications of a single ancestral gene, diverging over hundreds of millions of years.
Evolution of Genes with Novel Functions
Gene duplication can lead to novel functions when one copy diverges significantly from the original.
Example: The genes encoding lysozyme (antibacterial enzyme) and α-lactalbumin (milk-production protein) diverged from a duplicated ancestral lysozyme gene in mammals.
Exon duplication and exon shuffling (rearrangements of exons between genes) can create new protein combinations and functionalities.
Example: The gene for tissue plasminogen activator (TPA) arose through exon shuffling, combining exons from other proteins.
Role of Transposable Elements in Genome Evolution
Transposable elements (TEs) influence genome evolution by:
Facilitating chromosomal rearrangements and recombination.
Disrupting or altering gene expression by inserting into coding or regulatory regions.
Carrying genes or exons to new genomic locations, promoting genetic diversity and innovation.
In a Nutshell
Genome evolution involves DNA duplication, rearrangements, mutations, and the activity of transposable elements. These processes increase genetic diversity, enable new gene functions, and contribute significantly to the formation of new species and complex genomes.