Studying genetic mechanisms of change can provide insight into large-scale evolutionary change An organism’s genome is the full set of genes it contains. In eukaryotes, most of the genes are found in the nucleus, but genes are also present in plastids and chloroplasts.
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Figure 26.8 A Large Proportion of DNA Is Noncoding
If only the protein and RNA coding portions of genomes are considered, there is much less variation in size.
Figure 26.7 Complex Organisms Have More Genes than Simpler Organisms
Much of the noncoding DNA does not appear to have a function.
But it can alter the expression of surrounding genes.(regulatory genes)
Some noncoding DNA consists of pseudogenes (duplicated genes which are nonfunctional).
Some consists of transposable elements (repetetive DNA sequences that can move to different locations in the genome)
Nucleic acids or genes evolve when nucleotide base substitutions occur.
Substitutions can change the amino acid sequence, and thus the structure and function, of the polypeptides.
By characterizing nucleic acid sequences and the primary structures of proteins, molecular evolutionists can determine how rapidly these macromolecules have changed and why they changed.
Nucleotide substitutionsmay result in amino acid replacements.
Change in the amino acid sequence can change the charges, secondary and tertiary structure of a protein, and thus its function.
Evolutionary changes are determined by comparing nucleotide or amino acid sequences among different organisms.
The longer two sequences have been evolving separately, the more differences they accumulate.
The timing of evolutionary changes can be determined and causes can be inferred.
Animation: Allometric Growth
(a) Differential growth rates in a human
(b) Comparison of chimpanzee and human skull growth
with a single Hox cluster
with two Hox clusters
Vertebrates (with jaws)
with four Hox clusters
Hox gene 6
Hox gene 7
Hox gene 8
About 400 mya
(a) Patch of pigmented cells
(c) Pinhole camera-type eye
(d) Eye with primitive lens
(e) Complex camera-type eye
divergence of gene
(a) Orthologous genes
Gene duplication and divergence
Species A after many generations
(b) Paralogous genes
Number of mutations
Divergence time (millions of years)
Index of base changes between HIV sequences