BSCI Topic 9: Evolution of Genes and Genomes: Molecular Evolution

Noncoding DNA

DNA that doesn’t code for proteins (e.g., introns, regulatory regions)

Synonymous Substitution

DNA change with no amino acid change (neutral)

Nonsynonymous Substitution

DNA change alters amino acid (may affect fitness)

Missense Mutation

Changes one amino acid

Nonsense Mutation

Converts codon into stop codon

Neutral Theory (Kimura)

argues that most evolutionary changes at the molecular level, such as changes in protein sequences, are caused not by natural selection but by genetic drift acting on neutral mutations

Most mutations are neutral; evolution driven by drift

Genome Size Variation

refers to the wide diversity in the amount of DNA found in the genomes of organisms, ranging from very small to very large across different species

Due to repetitive and noncoding DNA

Transposable elements

Genome sequences that move within genome (“jumping genes”—Discovered by Barbara McClintock)

Lateral Gene Transfer

Genes transferred between species (Common in bacteria)

Pseudogenes

Nonfunctional gene copies

Gene Duplication

New genes form from copies; allows new functions

Molecular Clock

uses the rate at which DNA mutations accumulate to estimate the time of evolutionary events

Mutations accumulate at a constant rate; used to date divergences

Developmental Genes; Maternal Effect Genes

genes expressed by the mother (in her germ line) that produce products, such as RNA or proteins, deposited into the egg

Establish body axes

Developmental Genes; Gap Genes

set of genes in early insect embryonic development, such as in the fruit fly Drosophila, that respond to maternal gradients to define broad regions of the embryo's body along its anterior-posterior axis

Define broad body regions

Developmental Genes; Pair-Rule Genes

divide the embryo into periodic units of alternating segments

Mutations result in the loss of pattern in alternate segments, essentially producing half the normal number of segments

Divide embryo into segments

Developmental Genes; Segment-Polarity Genes

establish and maintain the distinct pattern within each segment of a developing embryo

Define segment boundaries

Developmental Genes; Hox Genes

regulatory genes that determine the basic body plan of animals by specifying the identity of body segments along the head-to-tail axis

Control body patterning

Genetic toolkit

set of genes shared throughout the animal kingdom due to evolutionary relatedness of life on earth

Conserved developmental genes used across species

Genetic Switches

Regulatory DNA turning genes on/off in specific tissues

Heterometry

Change in the amount of gene expression

Hererochrony

Change in timing of the expression

Heterotopy

Change in location of gene expression

Molecular evolution

applying evolutionary principles to analyze and manipulate genetic and molecular data.

By understanding how molecules like DNA, RNA, and proteins have changed over time, scientists can address challenges in medicine, forensics, conservation, and biotechnology

1. Understand how changes in gene expression often shape evolution:

often shape evolution more than changes to the protein-coding genes themselves, leading to new traits and adaptations without altering the protein's structure