Chapter 20.6: Molecular Evolution

Molecular Evolution

he process of evolution at the level of DNA sequences and proteins.

• Explains how genetic differences accumulate between species or populations over time due to mutation, selection, and genetic drift.

Diverge Genetically

•  the accumulation of genetic differences (mutations) between isolated populations or species

  • With time the independent mutations causes the population to diverge and the DNA sequences become increasingly different

LUCA

• LUCA stands for “Last Universal Common Ancestor”--> EVidence…

  • Living organisms store information using a genetic code , with 64 “words” called codons, and when the genetic code was investigated it was to be very similar in all species, with only a small number of minor variations. 

    • The reason species are different is because the meanings of the 64 codons are organized and put together in different ways. 

  • The explanation for this consistency is that all species inherited it from a common ancestor. 

    • Some evidence for this is the fact that many key structures of cells such as ribosomes and enzymes are the same in all organisms, which can be traced back to LUCA. 

  • There were likely other forms of evolving life at the time, but they probably went extinct. 

Molecular Clock

•  model that uses the rate of molecular (DNA or protein) change to estimate the time since two species diverged from a common ancestor

  • Through the accumulation of mutations in genes

Molecular Clock Rates

The speed of molecular evolution depends on how strongly natural selection acts on a gene

Slow Clocks

• Have strong Negative Selection which remove harmful mutations

  • Genes that are crucial for survival evolve very slowly because most mutations are deleterious and are eliminated.

Fast Clocks

• Have weak or no selection occurring

  • Some genes evolve faster because mutations are neutral or not harmful

    • Since they no longer perform a function, mutations have no effect on fitness, so they accumulate freely

Human mutation rate

• Uses the assumption that mutations accumulate at a constant rate

• Human mutation rate was 1/10⁹yr (10^-9yr^-1)