Glossary - A |
Allele
| What it's not: |
The feminine form of Al. |
| What it is: |
One of two or more forms of a particular gene at a specific
position on a chromosome. For example, blue and brown
eyes in human beings are determined by different alleles
of the eye colour gene. |
Allelic Heterogeneity
| What it's not: |
A battle cry from ancient Sparta. |
| What it is: |
Different mutations in the same gene lead to the same
disease phenotype. In other words, deletions and point
mutations produce the same end result. This is true for
Duchenne Muscular Dystrophy, where 70% of mutations are
due to large deletions in the dystrophin gene but the
rest of the mutations are a mixed bag. Interestingly,
the current genetic testing only finds the deletions;
so even if the testing is negative, other mutations can
still exist. In this case, a linkage analysis has to be
done to determine if you’re at risk for a mutated
dystrophin gene. |
Alternative Splicing
| What it's not: |
The way thieves have to hotwire new hybrid cars |
| What it is: |
The process where the initial strand of RNA copied directly from DNA is cut up (spliced) into different
mRNA strands without introns. Basically, different combinations
of exons are joined to create different proteins from
the same initial RNA (and same DNA sequence). Thus, one
gene can be the source of several proteins that differ
in function, timing or place of action. For example, alternative
splicing can make one isoform ‘brain-specific’
and another ‘muscle-specific’. It is estimated
that at least half of the genes in the human genome undergo
alternative splicing, which may help explain why our genome
has fewer genes that originally expected. |
Amino Acid
| What it's not: |
A cleaning solvent to remove tough grease, used by mechanics everywhere |
| What it is: |
Amino acids are building blocks for proteins. Composed of carbon,
hydrogen and nitrogen, these organic molecules all contain
a basic amino group (NH2) and an acidic carboxyl group
(COOH). Hence the truly logical moniker, amino acid. To
keep on living and loving, we humans need 20 of them.
Our bodies make 12 and we get the other 8 (the 8 essential
amino acids) from our food. |
Amniocentesis
| What it's not: |
A strange tickling sensation at the back
of your neck
|
What it is:
|
Amniocentesis is a prenatal procedure
that examines the chromosomes of fetal cells. It involves removing
a small amount of fluid from around the developing baby (amniotic fluid)
with a needle through the woman’s abdomen into the uterus. The amniotic
fluid has some of the baby’s cells that can undergo various lab tests.
It is commonly used to diagnose chromosome conditions (like Down syndrome)
and to diagnose genetic conditions (like cystic fibrosis) in the pregnancy.
It can be done at 15 weeks and later in a pregnancy. There is about
a 1 in 200 risk of miscarriage associated with this procedure.
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Amniotic Fluid
| What it's not: |
One of the lesser known, but essential
fluids in your car's transmission |
What it is:
|
The fluid surrounding the fetus in the
uterus. It is mostly water but also has cells sloughed off from
the fetus, secretions from the placenta and fetal urine. These fetal
cells can be examined for chromosomal and genetic disorders.
|
Apoptosis
| What it's not: |
A mild, incommunicable disease acquired from eating
too many Pop Tarts. |
| What it is: |
The normal method for disposing of unwanted cells. Otherwise
known as programmed cell death, apoptosis is a deliberate
‘suicide’ where a cell dies in an organized
way and no harmful bits are released. The cell shrinks,
its contents dissolve, its DNA is fragmented and the neighboring
cells take up (phagocytose) the leftovers. Apoptosis can
be triggered by damage and aging, and it’s also
normal in fetal development. The cells between our fingers
and toes, for example, undergo apoptosis so we are not
born with webbed hands and feet. Handy.
(Note: The terms 'programmed cell death' and apoptosis
are used interchangeably; but technically speaking, ‘pcd’
refers to the whole process, while apoptosis refers to
the structural changes the cell undergoes while dying.)
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Autoimmune Disease
| What it's not: |
A nervous disorder compelling the sufferer to buy a
new car every year |
| What it is: |
In autoimmune diseases, the immune system has been misdirected
to attack the body’s own cells and tissues. In rheumatoid
arthritis, for example, autoimmune response causes damage
in the joints; and an autoimmune response in the gut accompanies
celiac disease. Although the reason why the response happens
in the first place is unknown, it appears that some people
may have a genetic predisposition to autoimmune disorders.
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Autosome
| What it's not: |
A fancy word for 'garage' |
| What it is: |
A fancy word for the chromosomes other than the
sex chromosomes. We human beings have 22 pairs of autosomes
(chromosomes 1-22) and two sex chromosomes, two Xs if
you’re lucky enough to be female and XY if you’re
equally lucky enough to be male. |
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