Transcript millions of years ago

Box 24.1, Figure 1
Percentage of amino acids in hemoglobin
that are different between species
0.9
0.7
0.5
0.3
0.1
Time (millions of years ago)
0
100
200
300
400
500
The origin of HIV
• In 2000, researchers at the Los Alamos National
Laboratory in New Mexico used a molecular clock to date
the origin of HIV infections in humans
• We know HIV descended from related viruses tha affect
chimpanzees and another primate, the sooty mangabey
• The researchers sampled HIV from patients infected with
HIV just a few years apart
• The results indicated that the 1930’s were the probable
time when HIV first invaded humans
The accuracy of molecular clocks
• Molecular clocks can help assess the relative
chronology of branching in a phylogeny
• However, no genes mark time with precise
accuracy in their rates of nucleotide changes
(mutations)
• Molecular clocks are therefore accurate only in the
statistical sense of a fairly smooth average rate of
change
– Over time, there may still be chance deviations above
and below that average rate
The geologic time scale
• The earth’s history is divided into four eras:
– Precambrian - beginning when earth was formed (4.6 billion years
ago) and ending 600 million years ago
– Cambrian - from 600 million years ago to 245 million years ago
– Mesozoic - from 245 million years ago to 65 million years ago
– Cenozoic - from 65 million years ago to now
Geological periods
• The three most recent eras are divided into periods
• Paleozoic Era
–
–
–
–
–
–
Cambrian - 600 mybp until 510 mybp
Ordovician - 510 mybp until 440 mybp
Silurian - 440 mybp until 410 mybp
Devonian - 410 mybp until 360 mybp
Carboniferous - 360 mybp until 290 mybp
Permian - 290 mybp until 245 mybp
Geological periods
• Mesozoic Era
– Triassic - 245 mybp until 205 mybp
– Jurassic - 205 mybp until 145 mybp
– Cretaceous - 145 mybp until 65 mybp
• Cenozoic Era
– Tertiary - 65 mybp until 35 mybp
– Quaternary - 35 mybp until now