Transcript Beadle and Tatum 2

Blueprint of Life
Topic 16: Beadle and Tatum
Biology in Focus, HSC Course
Glenda Childrawi, Margaret Robson and Stephanie Hollis
DOT POINT(s)
 analyse information from secondary sources to
outline the evidence that led to Beadle and Tatum’s ‘one
gene – one protein’ hypothesis and to explain why this
was altered to the ‘one gene – one polypeptide’
hypothesis.
Introduction
The phenotype of an organism
is its total appearance
determined during
development by an interaction
between its genetic make-up
(genotype) and the
environment.
themetapicture.com
Introduction
A genome is all of the genetic material (DNA) within a cell and is
specific to each organism. Genomes influence nearly all the traits
or phenotypes, such as eye colour, height and susceptibility to
disease, and most variations occur due to differing genomes.
www.rsc.org
Introduction
The phenotypic appearance is
therefore directly affected by
gene expression. The extent of
phenotypic differences depends
on how different the DNA
sequences are in individuals, but
may also be influenced by the
environment. To what extent
differences in genotype cause
differing phenotypes has always
been of interest to people.
ravenousaddict.deviantart.com
Introduction
The proposal that a gene is
responsible for the production
of a specific protein was first
put forward by Archibald
Garrod in 1909. This idea,
together with work on the
inheritance of eye colour in
Drosophila, led biologists to
investigate the importance of
genes in enzyme production.
www.dec.ufcg.edu.br
Beadle and Tatum
George Beadle and Edward Tatum (1941) worked on mutants of
the fungus Neurospora crassa (a mould), leading to their
groundbreaking discovery that genes provide the instructions for
making proteins.
sandwalk.blogspot.com
Beadle and Tatum
They put forward the hypothesis
that one gene controls the
production of one enzyme. This was
based on observations made in
Beadle’s earlier experiments on
fruit flies—he found that if fruit
flies with normal eye colour were
exposed to X-rays, their offspring
would show a change in eye colour.
He hypothesised that this occurred
as a result of a defective enzyme for
the eye pigment.
news.sciencemag.org
Beadle and Tatum
Since evidence was needed to
support this hypothesis, Beadle
and Tatum designed and carried
out an experiment to attempt
to mutate genes of the mould
Neurospora crassa, the enzyme
functioning of which they could
test fairly simply.
www.dnaftb.org
Beadle and Tatum
Experimental evidence led them to propose a hypothesis that
genes affect enzyme production—the details of this were later
modified as the understanding of the relationship between genes
and proteins advanced.
www.readcube.com
Beadle and Tatum’s Experiment
It is important to remember that
at the time that Beadle and
Tatum began their research,
biologists were still not sure of
the chemical nature of the
heredity material—there was
still ongoing debate as to
whether it would prove to be
protein or DNA. This is why
their discovery was such a major
breakthrough.
pinterest.com
Activity
Visit website and do activity together (10-15min):
http://www.dnalc.org/resources/nobel/beadle_tatum.html
pinterest.com
Beadle and Tatum’s Experiment
Beadle and Tatum’s ‘one gene—
one enzyme’ hypothesis changed
to the ‘one gene—one protein’
hypothesis, once it was
demonstrated that there are
other proteins besides enzymes
that are encoded by genes.
sandwalk.blogspot.com
Beadle and Tatum’s Experiment
After the discovery by biologists
that one gene is not necessarily
responsible for the structure of
an entire protein, but for each
polypeptide chain making up
that protein, the current one
gene—one polypeptide
hypothesis was adopted. This is
the currently accepted theory
and has stood up to rigorous
testing, holding true for all
predictions so far.
users.rcn.com
Beadle and Tatum’s Experiment
George Beadle and Edward Tatum’s discovery won them the
Nobel Prize for Physiology or Medicine in 1958.
www.readcube.com -
Activity/Homework
-Students to visit site and go through experiment again on their
own.
http://www.dnalc.org/resources/nobel/beadle_tatum.html
a