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GENETICS
Genetics is the study of the function and behavior of genes. Genes,
the basic units of heredity, are biochemical instructions composed
of DNA (deoxyribonucleic acid) and are found inside the cells of
every organism, from bacteria to humans. An organism’s genes,
which reside in one or more chromosomes, determine its characteristics,
or traits. The sum of all an organism’s genes is called its
genome. In other words, the genome is divided into chromosomes, chromosomes
contain genes, and genes are made of DNA.
Geneticists seek to understand
how the information encoded in genes is used and controlled by cells
and how it is transmitted from one generation to the next. They also
study how tiny variations in genes can disrupt an organism’s
development or cause disease.
The term classical genetics refers to
the techniques and methodologies of genetics that predate the advent
of molecular genetics, which studies the structure and function of
genes at a molecular level. Classical genetics, which remains a basis
for all other topics in genetics, primarily is concerned with the
method by which genetic traits are transmitted in plants and animals.
These traits are classified as dominant (always expressed), recessive (subordinate to a dominant trait), intermediate (partially expressed)
or polygenic (due to multiple genes). In addition, the traits are
either sex-linked (result from the action of a gene on one of the
sex chromosomes) or autosomal (result from the action of a gene on
a chromosome other than a sex chromosome).
Classical genetics began
with Austrian monk Gregor Mendel, who traced the inheritance patterns
of certain traits in pea plants and showed they could be described
mathematically (“Mendel’s laws”).
Mendel’s 1865 publication, Experiments
on Plant Hybridization,
went largely unnoticed until the early 20th century. The patterns
of inheritance that Mendel observed still are employed for the study
of genetic diseases.
Molecular genetics employs the methods of genetics
and molecular biology, the branch of biology that deals with the
formation, structure and function of macromolecules essential to
life (such as nucleic acids and proteins) and especially with their
role in cell replication and the transmission of genetic information.
The avenues of investigation open to geneticists were broadened greatly
by the elucidation of the structure of DNA by James Watson and Francis
Crick, in 1953. In the 1970s, the discovery of restriction
enzymes (which catalyze the cleavage of DNA at specific sites to produce
discrete fragments) permitted scientists to begin sequencing genes
(determining the exact order of the four subunits of DNA — adenine,
guanine, cytosine and thymine); cloning genes (producing a replica
of a gene from one organism); and moving genes from one organism
to another to create genetically modified organisms
(GMOs). The latter
two procedures are known collectively as recombinant
DNA technology or genetic
engineering.
Subdisciplines of Genetics
Population, quantitative and ecological
genetics: Population, quantitative and ecological genetics, all very
closely related subfields, build on classical genetics (supplemented
with modern molecular genetics). Though all three study populations
of organisms, they differ somewhat in their focus. Population
genetics studies the distribution of and change in the frequencies of genes
under the influence of evolutionary forces, such as natural selection,
mutations and migration. Quantitative genetics, which builds on population
genetics, is the study of continuous traits (such as height or weight)
that do not have straightforward Mendelian inheritance because they
result from the interaction of many different genes. Ecological
genetics again builds on the basic principles
of population genetics but is focused more explicitly on ecological
issues, such as the relationship between species and their environments.
Medical
genetics: Medical genetics is the application of genetics to medicine.
Medical genetics encompasses many different individual fields, including
clinical genetics (the diagnosis and treatment of genetic diseases),
cytogenetics (the study of chromosomes under a microscope), molecular
genetics and genetic counseling (education
and guidance offered by professional advisors to help people make
informed decisions based on personal genetic information).
Behavioral
genetics: Behavioral genetics examines the role of genetics
in animal behavior. In humans, behavioral genetics studies the genetic
basis of personality as well as the causes and effects of human disorders
such as mental illness, substance abuse, violence and social attitudes.
Genomics: Genomics examines large-scale genetic patterns across the genome
for a given species. The information derived from genome sequence
data further reveals what genes do, how they are controlled and how
they work together. The now-completed Human
Genome Project has created
a genetic blueprint for building a human being. This vital information
will enable researchers to discover the genetic contributions to
diseases, develop highly effective diagnostic tools and treatments
and understand the health needs of people based on their individual
genetic makeups.
Related Links
http://www.accessexcellence.org/AE/AEPC/NIH/index.html
Understanding Genetic Testing, Access Excellence
http://encarta.msn.com/encyclopedia_761563786/Genetics.html
Genetics, Microsoft Encarta Online Encyclopedia
http://www.genome.gov/10000464
Online Genetics Education Resources, National Human Genome Research
Institute
http://www.genome.gov/10005911
Genetic Education Modules for Teachers
http://www.genome.gov/11006943
The Human Genome Project Completion FAQs
http://www.kumc.edu/gec
Genetics Education Center, University of Kansas Medical Center
http://learn.genetics.utah.edu
Genetic Science Learning Center, University of Utah
http://en.wikipedia.org/wiki/Genetics
Genetics, Wikipedia
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