Doing
Science
More about evolution
. . .
DNA and inheritance
DNA carries genetic (hereditary)
information. How do we know that?
- Results of DNA-specific
dye (1920s)
- transforming material
- Griffith (1920s)
- Avery, MacLeod and
McCarty (1944)
- Hershey and Chase (1952):
35S and 32P labels
Composition and Structure
of DNA
- Chargaff's experiment
(1950) A=T and G=C
- Wilkins and Franklin
(early 1950s) - X-ray crystallography
- Watson and Crick (1953)
"four bases, double-stranded right-handed helix, uniform diameter, antiparallel"
Its structure implies its
function: It must . . .
- store a lot of information
- be susceptible to mutation
- replicate precisely in
the cell cycle
- and it must be expressed
in the phenotype
DNA Replication
- Kornberg (1956) -
in vitro
- Meselson and Stahl (1957)
- semiconservative
DNA and the phenotype (the
observable characteristics of the organism)
- A section of DNA codes
for the amino acid sequence of a specific protein
- These proteins, along
with environmental influences, determine the structure and functioning of
the organism
- The section of DNA that
codes for a protein is called a "gene"
- Variations in that location
on the DNA strand are called "alleles"
What are mutations?
- Mutations create new
alleles, the variation that is the raw material of evolution
- Under natural selection,
some alleles become more frequent in the population, while others become less
frequent
- The modern definition
of evolution is "change in allele frequencies in a population"
- Types of mutations:
- Point mutations (single
nucleotide): synonymous, missense, nonsense, frameshift
- Chromosomal: deletion,
duplication, inversion, translocation
These topics are covered in any good general biology book, such as Life:
the Science of Biology, by Purves, Sadava, Orians, and Heller.