bodies contain millions of cells which contain our genetic
information. Within each cell there is a nucleus. Within
each nucleus there are 46 chromosomes arranged in pairs
(23 pairs in total).
The 23rd pair are the sex chromosomes.
are two chromosomes in each numbered pair because an
individuals always inherits one copy from the egg from
their mother, and one copy from the sperm of their father.
Individuals with two X chromosomes are female while
individuals who have an X and a Y chromosome are male.
should only have two in each pair. If an individual has
a different number than two chromosomes in each pair they
have a chromosome abnormality. The most commonly talked
about chromosome abnormality is Down syndrome, also known
as trisomy 21, since the condition primarily is caused
by the presence of an extra chromosome 21.
an individual has a structural rearrangement on one of
the chromosomes they also have a type of chromosome abnormality.
Two common types of structural chromosomal rearrangements
include a translocation and an inversion.
A translocation is where a piece of one chromosome breaks
off and attaches to another chromosome. An inversion is
where a particular segment of a chromosome has inverted
is an example of a balanced structural
constitutional chromosome abnormality. Part of
chromosomes 5 and 8 have broken and exchanged.
These patients are usually phenotypically normal,
but have an increased risk of miscarriages and
addition to chromosome conditions there also exists
genetic conditions. A genetic condition affects a particular
gene and not the entire chromosome. We have thousands
of genes located throughout each chromosome, each with
their own unique function. The genes that are situated
on chromosome 1 are different than the genes found on
chromosome 21. When there is a change in the gene that
affects its structure or function we call that a mutation.
Some mutations are harmless, other cause significant
physical and/or mental impairments.
is helpful to seek genetic counselling when there is
a known familial mutation to talk about options for
testing, potential risks for future future pregnancies
and for family members. It is also helpful to discuss
effective coping mechanisms for dealing with the issues
associated with having a genetic disorder within the
family (i.e., caring for an affected relative, understanding
a genetic diagnosis, dealing with at-risk status, understanding
reproductive choices, risks for stigmatization, insurance