Name
Class
Date
17.4 Molecular Evolution
Lesson Objectives
Explain how molecular clocks are used.
Explain how new genes evolve.
Describe how Hox genes may be involved in evolutionary change
Lesson Summary
Timing Lineage Splits: Molecular Clocks A molecular clock uses mutation rates
in DNA to estimate the length of time that two species have been evolving independently.
Molecular clock models assume that neutral mutations, which do not affect phenotype,
accumulate in the DNA of different species at about the same rate.
Two species evolving independently from each other will accumulate different neutral
mutations through time. The more differences between the DNA, the more time has passed
since the two species shared an ancestor.
Gene Duplication New genes evolve through the duplication, and then modification, of
existing genes.
Organisms may carry multiple copies of the same gene. The extra copies of a gene may
undergo mutations.
The mutated gene may have a new function that is different from the original gene. In this
way, new genes evolve.
Multiple copies of a duplicated gene can turn into a gene family.
Developmental Genes and Body Plans Researchers study the relationship between
evolution and embryological development.
Some genes, called Hox genes, control the forms of animals’ bodies.
Small changes in Hox genes during embryological development can produce major changes
in adult organisms.
Some scientists think that changes in Hox genes may contribute to major evolutionary
changes.
Timing Lineage Splits: Molecular Clocks
1. What is a molecular clock?
2. Why are only neutral mutations useful for molecular clocks?
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