Similar patterns of embryonic development and shared master genes that control development reflect common ancestry between species. Highly similar DNA and protein sequences, especially in genes that guide development, provide evidence that more closely related species evolved from a shared ancestor. Differences in gene expression between species can lead to differences in body form, as seen when comparing chickens and snakes. Protein sequences are also compared between species, and fewer differences are observed between more closely related lineages.

1. Chapter 16
Evidence of Evolution
Section 16.8

2. © Cengage Learning 2015
16.8 How Do Similarities In DNA and
Protein Reflect Evolution?
• Similar patterns of embryonic development reflect shared
ancestry
– Master genes that control embryonic development patterns
have changed very little or not at all over evolutionary time
– Master genes with similar sequence and function in different
lineages are strong evidence that those lineages are related

3. © Cengage Learning 2015
How Do Similarities In DNA
and Protein Reflect Evolution? (cont’d.)
Figure 16.15 Visual comparison of vertebrate embryos. All vertebrates go through an
embryonic stage in which they have four limb buds, a tail, and divisions called somites
along their back. From left to right : human, mouse, bat, chicken, alligator.

4. © Cengage Learning 2015
How Do Similarities In DNA and Protein
Reflect Evolution? (cont’d.)
• Homeotic genes
– Master genes
– Guide formation of specific body parts during development
– Example: Hox genes
– Similar genes give rise to similar proteins
– Proteins are also commonly compared
• The amino acid sequence of a protein is compared between several
species

5. © Cengage Learning 2015
How Do Similarities In DNA and Protein
Reflect Evolution? (cont’d.)
• Similarities in patterns of animal development occur
because the same genes direct the process
– Similar developmental patterns—and shared genes—are
evidence of common ancestry, which can be ancient
• Mutations change the nucleotide sequence of each
lineage’s DNA over time

6. © Cengage Learning 2015
How Do Similarities In DNA and Protein
Reflect Evolution? (cont’d.)
• There are generally fewer differences between the DNA of
more closely related lineages
• Similar genes give rise to similar proteins
• Fewer differences occur among the proteins of more
closely related lineages

7. © Cengage Learning 2015
How Do Similarities In DNA and Protein
Reflect Evolution? (cont’d.)
Figure 16.16 How differences in body form arise from differences in master gene
expression. Expression of the Hoxc6 gene is indicated by purple stain in two vertebrate
embryos, chicken (left) and garter snake (right). Expression of this gene causes a
vertebra to develop ribs as part of the back. Chickens have 7 vertebrae in their back
and 14 to 17 vertebrae in their neck; snakes have upwards of 450 back vertebrae and
essentially no neck.

8. © Cengage Learning 2015
How Do Similarities In DNA and Protein
Reflect Evolution? (cont’d.)
Figure 16.17 Example of a protein comparison. Here, part of the amino acid sequence
of mitochondrial cytochrome b from 20 species is aligned. This protein is a crucial
component of mitochondrial electron transfer chains. The honeycreeper sequence is
identical in ten species of honeycreeper; amino acids that differ in the other species are
shown in red. Dashes are gaps in the alignment.