'''Genetics''' (from the
Greek genno
γεννώ= give birth) is the
science of
genes,
heredity, and the
variation of
organisms. The word genetics was first applied to describe the study of inheritance and the science of variation by English scientist
William Bateson in a letter to Adam Sedgewick, dated
April 18, 1905.
Humans began applying knowledge of genetics in prehistory with the
domestication and
breeding of plants and animals. In modern research, genetics provides important tools in the investigation of the function of a particular gene, e.g. analysis of
genetic interactions. Within
organisms, genetic information generally is carried in
chromosomes, where it is represented in the
chemical structure of particular
DNA molecules.
Genes encode the information necessary for synthesizing proteins, which, in turn play a large role in influencing, although, in many instances, do not completely determine, the final
phenotype of the organism.
The phrase
to code for is often used to mean a
gene contains the instructions on how to build a particular
protein, as in
the gene codes for the protein.
Note that the "one gene, one protein" concept is now known to be simplistic. For example, a single gene may produce multiple products, depending on how its
transcription is regulated.
History
It was not until 1865 that
Gregor Mendel first traced inheritance patterns of certain traits in pea plants and showed that they obeyed simple statistical rules. Although not all features show these patterns of
Mendelian inheritance, his work acted as a proof that application of statistics to inheritance could be highly useful. Since that time many more complex forms of inheritance have been demonstrated.
From his statistical analysis Mendel defined a concept that he described as an
allele, which was the fundamental unit of heredity. The term
allele as Mendel used it is nearly synonymous with the term
gene, whilst the term
allele now means a specific variant of a particular gene.
The significance of Mendel's work was not understood until early in the twentieth century, after his death, when his research was re-discovered by other scientists working on similar problems.
Mendel was unaware of the physical nature of the gene. We now know that genetic information is normally carried on
DNA. (Certain viruses store their genetic information in
RNA). Manipulation of
DNA can in turn alter the inheritance and features of various organisms.
Timeline of notable discoveries
:1859
Charles Darwin publishes
The Origin of Species
:1865
Gregor Mendel's paper,
Experiments on Plant Hybridization
:1903
Chromosomes are discovered to be hereditary units
:1905 British biologist
William Bateson coins the term "genetics" in a letter to Adam Sedgwick
:1910
Thomas Hunt Morgan shows that genes reside on chromosomes
:1913
Alfred Sturtevant makes the first genetic map of a chromosome
:1918
Ronald Fisher publishes
On the correlation between relatives on the supposition of Mendelian inheritance - the modern synthesis starts.
:1913 Gene maps show chromosomes containing linear arranged genes
:1927 Physical changes in genes are called
mutations
:1928
Frederick Griffith discovers a hereditary molecule that is transmissible between bacteria (see
Griffiths experiment)
:1931 Crossing over is the cause of
recombination
:1941
Edward Lawrie Tatum and
George Wells Beadle show that genes code for
proteins; see the original central dogma of genetics
:1944 Oswald Theodore Avery,
Colin McLeod and
Maclyn McCarty isolate
DNA as the genetic material (at that time called transforming principle)
:1950
Erwin Chargaff shows that the four nucleotides are not present in nucleic acids in stable proportions, but that some general rules appear to hold (e.g., that the amount of adenine, A, tends to be equal to that of thymine, T).
Barbara McClintock discovers
transposons in
maize
:1952 The
Hershey-Chase experiment proves the genetic information of
phages (and all other organisms) to be DNA
:1953 DNA structure is resolved to be a double
helix by
James D. Watson and
Francis Crick
:1956 Jo Hin Tjio and Albert Levan established the correct
chromosome number in humans to be 46
:1958 The
Meselson-Stahl experiment demonstrates that DNA is
semiconservatively replicated
:1961 The
genetic code is arranged in triplets
:1964 Howard Temin showed using
RNA viruses that Watson's central dogma is not always true
:1970 Restriction enzymes were discovered in studies of a bacterium,
Haemophilius influenzae, enabling scientists to cut and paste DNA
:1977 DNA is
sequenced for the first time by Fred Sanger,
Walter Gilbert, and Allan Maxam working independently. Sanger's lab complete the entire genome of sequence of Bacteriophage Φ-X174;.
:1983 Kary Banks Mullis discovers the
polymerase chain reaction enabling the easy amplification of DNA
:1989 The first human gene is sequenced by
Francis Collins and
Lap-Chee Tsui, it encodes the
CFTR protein, defects in this gene cause
cystic fibrosis
:1995 The genome of
Haemophilus influenzae is the first genome of a free living organism to be sequenced
:1996 Saccharomyces cerevisiae is the first
eukaryote genome sequence to be released
:1998 The first genome sequence for a multicellular eukaryote,
C. elegans is released
:2001 First draft sequences of the human genome are released simultaneously by the
Human Genome Project and
Celera Genomics.
:2003 (14 April) Successful completion of Human Genome Project with 99% of the genome sequenced to a 99.99% accuracy
http://www.genoscope.cns.fr/externe/English/Actualites/Presse/HGP/HGP_press_release-140403.pdf
Areas of genetics
Classical genetics
Main articles: Classical genetics,
Mendelian inheritance
Classical genetics consists of the techniques and methodologies of
genetics that predate the advent of
molecular biology. After the discovery of the
genetic code and such tools of
cloning as
restriction enzymes, the avenues of investigation open to geneticists were greatly broadened. Some classical genetic ideas have been supplanted with the mechanistic understanding brought by molecular discoveries, but many remain intact and in use, such as
Mendel's laws. Patterns of inheritence still remain a useful tool for the study of genetic diseases.
Molecular genetics
Molecular genetics builds upon the foundation of classical genetics but focuses on the structure and function of
genes at a
molecular level. Molecular genetics employs the methods of both classical genetics (such as hybridization) and
molecular biology. It is so-called to differentiate it from other sub fields of genetics such as
ecological genetics and
population genetics. An important area within molecular genetics is the use of molecular information to determine the patterns of descent, and therefore the correct
scientific classification of organisms: this is called
molecular systematics.
The study of inherited features not strictly associated with changes in the
DNA sequence is called
epigenetics.
Some take the view that
life can be defined, in
molecular terms, as the set of strategies which
RNA polynucleotides have used and continue to use to perpetuate themselves. This definition grows out of work on the
origin of life, specifically the
RNA world hypothesis.
Population, quantitative and ecological genetics
Main articles: Population genetics,
Quantitative genetics,
Ecological genetics
Population, quantitative and ecological genetics are all very closely related subfields and also build upon classical genetics (supplemented with modern molecular genetics). They are chiefly distinguished by a common theme of studying
populations of organisms drawn from nature but differ somewhat in the choice of which aspect of the organism on which they focus. The foundational discipline is population genetics which studies the distribution of and change in
allele frequencies of genes under the influence of the four evolutionary forces:
natural selection,
genetic drift,
mutation and
migration. It is the theory that attempts to explain such phenomena as
adaptation and
speciation.
The related subfield of quantitative genetics, which builds on population genetics, aims to predict the response to
selection given data on the
phenotype and relationships of individuals. A more recent development of quantitative genetics is the analysis of quantitative trait loci. Traits that are under the influence of a large number of genes are known as quantitative traits, and their mapping to a location on the
chromosome requires accurate phenotypic, pedigree and marker data from a large number of related individuals.
Ecological genetics again builds upon the basic principles of population genetics but is more explicitly focused on
ecological issues. While molecular genetics studies the structure and function of genes at a molecular level, ecological genetics focuses on wild populations of organisms, and attempts to collect data on the ecological aspects of individuals as well as molecular markers from those individuals.
Genomics
A more recent development is the rise of
genomics, which attempts the study of large-scale genetic patterns across the
genome for (and in principle, all the DNA in) a given species. Genomics depends on the availabilty of whole genome sequences, and compuational tools developed in the field of
bioinformatics for analysis of large set of data.
The science which grew out of the union of
biochemistry and genetics is widely known as
molecular biology.
The term "genetics" is often widely conflated with the notion of
genetic engineering, where the DNA of an organism is modified for some kind of practical end, but most research in genetics is aimed at understanding and explaining the effect of genes on phenotypes and in the role of genes in populations (see
population genetics and
ecological genetics), rather than genetic engineering.
See also
Publications
External links
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