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 organism as an integrated whole and attempt to answer questions such as: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 organism as an integrated whole and attempt to answer questions such as:Complex Organisms Have More Genes than Simpler Organisms
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 substitutions substitutions occur.may 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
Fig. 25-19 or amino acid sequences among different organisms.
(a) Differential growth rates in a human
(b) Comparison of chimpanzee and human skull growth
Fig. 25-20 development relative to the development of nonreproductive organs
Fig. 25-21 associated with alterations in
with a single Hox cluster
with two Hox clusters
Vertebrates (with jaws)
with four Hox clusters
Fig. 25-22 associated with alterations in
Hox gene 6
Hox gene 7
Hox gene 8
About 400 mya
Fig. 25-24 associated with alterations in
(a) Patch of pigmented cells
(c) Pinhole camera-type eye
(d) Eye with primitive lens
(e) Complex camera-type eye
Fig. 26-18 documented in its genome
divergence of gene
(a) Orthologous genes
Gene duplication and divergence
Species A after many generations
(b) Paralogous genes
Fig. 26-19 theoretically constant and equal to the neutral mutation rate, the concept of the molecular clock was developed.
Number of mutations
Divergence time (millions of years)
Fig. 26-20 theoretically constant and equal to the neutral mutation rate, the concept of the molecular clock was developed.
Index of base changes between HIV sequences