Transcript Molecular_Evolution

Molecular Evolution
The Genome: smaller than we
once thought
• The collection of all
the DNA in the cell is
referred to as the
genome.
• We now know that
most of the DNA does
not code for amino
acid sequences
• Non-coding segments
guide translation and
are called introns
• Coding segments are
called exons
Genes and Genomes
Interons may act as
promoters - the determine
when transcription will take
place
Transposable
elements
• maize plants which
develop speckled
kernels do not inherit
this phenotype in a
Mendelian fashion.
• Their color patterns
due to the action of
transposons moving in
and out of the genome.
• This process,
transposition, happens
in DNA, and RNA
Movable genes: Retrotransposon
• Retrotransposons ubiquitous components
of the DNA of many eukaryotic organisms.
abundant in plants, where they are often a
principal component of nuclear DNA.
• In maize, 49-78%
• wheat up to 90%
Selection
pressure
• Transposable
element
insertions are
selected against
when they exist
in exons, but not
in interons !
• Why not?
• The
importance
of the
tandem
array
• (Why sex
is
important)
The genetic clock
• Exons evolve at about one
substitution per billion years
• Interons evolve about 10x as
fast
• Why do you think the rate is
given as substitutions per
year- rather than per
generation?
•  Have you read “The
selfish gene”
Rate = K/(2T)
K= substitutions
The genetic clock
• Measuring Synonymous substitutions:
These that do not change the amino acid
composition
– such as a GGG to GGC change - both codons
still encode glycine
• Measuring non-synonymous substitutions
(Those that do change amino acid
composition)
– Is natural selection taking place?
• Natural selection4Answer 1 => 9 pg 164
• Molecular evolution 5
• Question 4,5,6,7,8, & 9 pg 186