Molecular clock, Neutral hypothesis and CSIR NET life sciences questions My youtube video: https://youtu.be/zI5e3wn5O9Q

1. MOLECULAR CLOCK HYPOTHESIS!
1
“A technique in molecular evolution to relate
the time that two species diverged to the
number of molecular differences measured
between the species DNA/ protein sequences”

2. Neutral theory by Kimura
“Large fraction of new mutations DO NOT have an effect on
evolutionary fitness, so natural selection neither favours nor
disfavours them”
2
Mutations
Fixed
Lost
Substitution Rate
Genetic Drift
Substitution Rate= Mutation Rate

3. Observations
3
Synonymous base substitution>Non-Synonymous base substitution
Mutation rate is higher in Non-coding sequences
Pseudogenes evolve at higher rate than functional genes

4. Calibrating
molecular clock
Absolute age of some
divergence event
- Fossil record
- Geological event
4
5% difference
1% per
million years
over a
period of 5
million years
Five fold
higher rate
over a
period of 1
million years

5. 5
r = D
2 t
r= rate of nucleotide substitutions
(per million years)
D= the proportion of base pairs that differ
between the two sequences
t= time of most recent common ancestor in
million years

6. 6
Using molecular clock, it was estimated that two species A and B must
have diverged from their common ancestor about 9 x 106
years ago. If
the rate of divergence per base pair is estimated to be 0.0015 per
million years, what is the proportion of base pairs that differ between
the two species now?
a. 0.0270 b. 0.0135 c. 0.00017 d. 0.0035
Ans: D= r x 2T= 0.0015 x 2 x 9 =0.0270