The C value paradox
1
• The C value:
– total amount of DNA in the genome
• We would expect that the more complex the
organism, the more DNA is needed to “run it”
– Therefore, we would expect a linear relationship
between genome size and organism complexity.
• This idea appears to make sense:
– the more complex the organism is, the more genetic
information it needs (larger C value)
– In smaller organisms (viruses, bacteria) there is no
room for excess DNA (smaller C value)
continued
2
• At the lower range of complexity, this holds:
• Bacteria have smaller genomes than eukaryotes,
and viruses have smaller genomes than bacteria.
• In larger organisms, relationship breaks down
– Organisms have DNA apparently in excess of what
is needed; repetitive sequences, “junk DNA”
• This is the C value Paradox, that in the most
complex organisms, there doesn’t appear to be
the expected relationship between complexity
and genome size.
Homework on the C Value Paradox
3
• What does this relationship look like?
– How does genome size change with the complexity
of the organism?
• How do you graph “complexity”?
– We will use actual physical size for complexity.
– You agree humans are more complex than
bacteria, and they more complex than viruses?
Directions
4
• You will be provided with a table of organisms.
– These are your independent variables: organism
size.
– You will sort through the sites and references
provided to determine the genome size for each
organism.
– The size ranges and the amount of base pairs vary
by orders of magnitude: log graph
– Directions for homework at
http://www.clt.astate.edu/dgilmore/Genetics/Genetic
s%20homework/genomesize.htm