Download Lecture 18

Cutting DNA:
Restriction enzymes
1. cleave DNA at specific recognition sites
a. is a bacterial defense mechanism
b. recognition sequences
“sticky ends”
Any DNA fragment cut with a particular enzyme can be
annealed to another DNA fragment cut with the same enzyme.
Hundreds of these enzymes now in use.
Use DNA ligase to “paste” DNA fragments together.
This is recombinant DNA.
a. DNA can be inserted into bacterial DNA (plasmids).
b. Genes can be also inserted into eukaryotic chromosomes.
DNA Fingerprinting
A. Use restriction fragment length polymorphisms (RFLPs)
1. digest DNA samples with a
panel of restriction enzymes
2. DNA from different
individuals should cut
differently
How do we visualize this?
Gel Electrophoresis
Separates DNA fragments by size
1. DNA carries a (-) charge.
2. Run current through an agarose gel.
3. Shorter fragments migrate faster.
DNA Fingerprint
Is an exclusionary tool
Polymerase Chain Reaction (PCR)
Method for amplifying small DNA samples
- taq DNA polymerase
cDNA
We want to make a functional protein. What’s the problem?
cDNA
We need a copy of the gene, but with the introns removed.
Copy the mRNA instead of the gene.
- reverse transcriptase
cDNA
DNA copy of an mRNA is called a cDNA.
The cDNA can be inserted into bacterial plasmid.
I. Early Ideas on Origin of Species
A. Genesis
a. written around 1446 BC
b. species are static; earth about 6000 years old
B. Anaximander
a. around 500 BC
b. life began in the sea
c. simpler organisms begat the more complex ones
C. Aristotle (384-322 BC)
- species do not change
D. Study of fossils (1700’s)
- began to spur belief that Earth was very old
E. Jean Baptiste Lamarck (1744-1829)
a. early advocate of evolution
b. “inheritance of acquired characteristics”
“All knowledge that is not the real product of observation,
or of consequences deduced from observation, is entirely
groundless and illusory.”
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
II. Charles Darwin
A. Five year voyage on the Beagle
1. Captain Robert FitzRoy
a. takes command after a suicide
b. a student of phrenology
c. a kidnapping “experiment” gone wrong
d. a hasty return to Tierra del Fuego for more
“mapping”
e. naturalist needed (really a companion for the
long journey)
2. Charles Darwin (1809-1882)
a. studied to become a clergyman (Cambridge)
b. interest in collecting plant and animal specimens
c. botany professor recommended him for the Beagle
B. South America and Galapagos islands (1831-1836)
1. species well-adapted to their environment
2. species “resembled” mainland organisms
3. fossils more similar to modern South American
species than to fossils on other continents
4. adaptation among finch species:
a. beak size and shape
b. influence feeding
c. environmental conditions influence survivability
(dry, wet)
C. Thomas Malthus (an economist)
1. Essay on the Principles of Population (1798)
a. populations of organisms increase geometrically
b. rate of reproduction too high to be sustained
c. warning against human overpopulation
2. but in nature, this does not seem to occur
3. Darwin’s answer: death (selection) limits population
numbers
4. This provided missing link for Darwin
D. Alfred Wallace
1. came to same conclusions while in Indonesia
2. published his findings along with Darwin (1858-59)
E. Darwin: On the Origin of Species by Means of Natural
Selection
1. descent with modification
2. closely related species likely from common ancestor
Darwin’s Theory
Hypothesis 1: Every organism has the potential to leave
more than one offspring.
Hypothesis 2: The number of individuals within a
species remains fairly constant over time.
Prediction A: If 1 and 2 are true, then not all individuals
realize their reproductive potential.
Hypothesis 3: Individuals within a species vary in terms
of their traits.
Hypothesis 4: At least some of these traits are inherited.
Prediction B: If A, 3, and 4 are true, then some
individuals are better suited for their environment,
leaving more offspring.
Their traits become more common.
Darwin’s Theory
Better suited individuals have inherited those traits, and
they pass them on to their offspring.
Survival of the fittest = Reproduction of the fittest.