Lecture #13—Mutation & the Molecular Clock

Mutations are abrupt changes in the genetic material. They occur primarily when the cells are duplicating their DNA just before cell division. Mutations that are relevant to evolution must occur in the reproductive organs (e.g. testes, ovary) in order to be potentially passed on to the next generation.

There are several categories of mutation:

  1. Structural Changes in the Chromosomes
  1. Loss or duplication of whole chunks of DNA

  1. Point mutations (Single base changes in the DNA)

a)Substitutions

b)Additions

c)Subtractions (deletions)

  1. Mutations in Developmental Genes

a)Shift is growth gradient so different organs develop at different rate (heterochronic mutations)

b)Homeotic mutations—mutations in Master Genes that control several genes.

Causes of mutation: radiation, chemicals, spontaneous, CRISPR (deliberate point mutation)

Mutation can improve, harm, or cause no change in evolutionary fitness.

Molecular Clock—We can compare the differences in the number of bases in DNA between species to determine i.e. how distantly they are related. If we know the average rate of mutation then we can estimate how long ago they had a common ancestor. This is a fundamental principle of evolution. But in order to determine the timing we have to rely on the fossil record to give us dates and from there we can extrapolate to other closely related organisms.

Terms/concepts to Define:

Mutation

Somatic mutations

Translocation

Transposition (transposons)

Inversions

Aneuploidy

Down syndrome

Polyploidy

Point mutations

Base substitution

Base addition

Base subtraction

Frame shift

Stop and start codons

Neotony

Homeotic mutation

CRISPR

Silent mutation

Evolutionary Fitness

Molecular Clock

Can you answer these questions?

  1. Suppose a man develops cancer because of a mutation in his pancreas, will this mutation have any impact on the evolution of the species?
  2. In what way will transposons possibly affect the function of the DNA?
  3. More mutations are found in people who are 55 than those who are 25. Please explain how this happens.
  4. Explain how some mutations can be said to be silent.
  5. Most of the DNA molecule does not code for protein, why do scientists use this region to count mutations that will determine their relatedness?
  6. When trying to calibrate the tempo of a molecular clock, why do scientists use an average mutation rate?