Barbara McClintock
(June 16, 1902 ? September 2, 1992) was an
American
biologist
. She was a distinguished
cytogeneticist
who worked on
inheritance
in
maize
. McClintock was awarded the 1983
Nobel Prize in Physiology or Medicine
.
McClintock got her
PhD
in
botany
from
Cornell University
in 1927. Maize cytogenetics was the focus of her research for the rest of her career.
[1]
From the late 1920s, McClintock studied
chromosomes
and how they change during reproduction in maize. She used
microscopic
analysis to show genetic recombination by
crossing-over
during
meiosis
?a mechanism by which chromosomes exchange information.
She produced the first
genetic map
for maize, and demonstrated the role of the
telomere
and
centromere
. These are regions of the chromosome that are important in preserving genetic information.
She was recognized amongst the best in the field, awarded prestigious fellowships, and elected a member of the
National Academy of Sciences
in 1944.
[2]
During the 1940s and 1950s, McClintock discovered
transposition
and used it to show how
genes
are responsible for turning physical characteristics on or off.
[3]
She developed theories to explain the control of genetic information from one generation of maize plants to the next. Encountering skepticism of her research and its implications, she stopped publishing her data in 1953. Later, she made an extensive study of the cytogenetics of maize
races
from South America.
McClintock's research became well understood in the 1960s and 1970s, as researchers discovered the mechanisms behind the genetic change and
gene regulation
that she had shown in her maize research in the 1940s and 1950s.
[4]
Awards and recognition for her contributions to the field followed for the discovery of
transposons
; she is the only woman to receive an unshared Nobel Prize in the category 'Physiology or Medicine'.
[5]
Discovery of controlling elements
[
change
|
change source
]
In the summer of 1944 at Cold Spring Harbor Laboratory, McClintock began systematic studies on the inheritance of colour patterns of
maize
seeds
. In early 1948, she made the surprising discovery that two
genetic loci
,
Dissociator
and
Activator
could transpose, or change position, on the chromosomes.
McClintock also found that the transposition of
Ds
and the is determined by the number of
Ac
copies in the cell.
Between 1948 and 1950, she developed a theory: these mobile elements regulated genes by inhibiting or modulating their action. She referred to
Dissociator
and
Activator
as "controlling units"?later, as "controlling elements"?to distinguish them from genes.
She suggested that
gene regulation
could explain how complex multicellular organisms made of cells with identical
genomes
have cells of different function. McClintock's discovery challenged the concept of the genome as a static set of instructions passed between generations.
In 1950, she reported her work on
Ac/Ds
and her ideas about gene regulation in a paper. In summer 1951, when she reported on her work on gene mutability in maize at the annual symposium at Cold Spring Harbor Laboratory.
[6]
Her work on controlling elements and gene regulation was difficult and was not immediately understood or accepted by her contemporaries; she described the reception of her research as "puzzlement, even hostility".
[7]
Nevertheless, McClintock continued to develop her ideas on controlling elements. She published a paper in 1953 where she presented all her statistical data, and undertook lecture tours to universities throughout the 1950s to speak about her work.
[8]
She continued to investigate the problem and identified a new element that she called
Suppressor-mutator
(
Spm
), which, although similar to
Ac/Ds
, displays more complex behavior.
- McClintock B. 1929. A cytological and genetical study of triploid maize.
Genetics
14
(2): 180?222. PMID
[3]
- McClintock B. 1950. The origin and behavior of mutable loci in maize. Proceedings of the National Academy of Sciences of the United States of America
36
(6): 344?355. PMC 1063197.
PMID 15430309
.
- McClintock B. 1953. Induction of instability at selected loci in maize. Genetics
38
(6): 579?599. PMC 1209627.
PMID 17247459
.
- McClintock B. 1961. Some parallels between gene control systems in maize and in bacteria.
The American Naturalist
95
(884): 265?277.
[4]
- ↑
McClintock, Barbara. 1983.
A short biographical note: Barbara McClintock
Nobel Foundation biography
Archived
2001-12-17 at the
Wayback Machine
.pdf
- ↑
"Barbara McClintock"
. The National Academies. Archived from
the original
on 28 November 2012
. Retrieved
9 January
2013
.
- ↑
Pray, Leslie; Zhaurova, Kira (2008), "Barbara McClintock and the Discovery of Jumping Genes (Transposons)", Nature Education, Nature Publishing Group,
1
(1).
[1]
- ↑
The Barbara McClintock papers.
[2]
- ↑
"Facts on the Nobel Prize in Physiology or Medicine"
. Nobelprize.org
. Retrieved
12 July
2010
.
- ↑
McClintock, Barbara. 1950. The origin and behavior of mutable loci in maize.
Proceedings of the National Academy of Sciences
.
36
:344?55.
- ↑
McClintock, Barbara. 1987. "Introduction" in
The discovery and characterization of transposable elements: the collected papers of Barbara McClintock
. ed John A. Moore. Garland Publishing.
ISBN
978-0-8240-1391-2
.
- ↑
McClintock, Barbara. 1953. Induction of instability at selected loci in maize.
Genetics
38
:579?99.
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