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Understanding Chromosomal Needs

Our bodies are composed of billions of cells. Stored inside each of our cells are structures called chromosomes. The purpose of chromosomes is to store all of our genes (DNA). A chromosome is like a bookshelf and our genes are like books; therefore, chromosomes are bookshelves to store our genes.  Individuals usually have 46 chromosomes that can be organized into 23 pairs (Figure 1). The pairs of chromosomes that are numbered 1 to 22 are found in everyone, both males and females. The 23rd pair of chromosomes are the sex chromosomes, which determine if we are male or female. Typically, males have one X and one Y chromosome, and females have two X chromosomes. We inherit our chromosomes from our parents; we get one copy of each chromosome from our mother and one from our father

What are Chromosome Changes? 

It is important that we have 46 chromosomes in total. However, sometimes a person can have a change in their chromosomes. Chromosome changes can include having too many or too few chromosomes or a difference in the structure of a chromosome. How a person is affected by a chromosome change depends on the specific change that the person has. The following are examples of some types of chromosome changes.

Too few and too many chromosomes

An example of a condition caused by too few chromosomes is Turner syndrome. Turner syndrome happens in females who have only one X chromosome instead of two. Therefore, they only have 45 chromosomes (45, X) instead of 46. 

An example of a condition caused by too many chromosomes is Down syndrome (trisomy 21), which is caused by having three copies of chromosome 21 instead of the usual 2 (see picture below).

A change in the structure of the chromosome

There are different ways that the structure of a chromosome can be changed. Some structural changes have little or no effect on a person, whereas other changes can have more significant effects. The effects and impacts vary greatly and you should always speak to your child’s medical team about the specifics for a child.  Some types of structural changes are:

  • Deletion: a piece of a chromosome is missing
  • Duplication: an extra piece of a chromosome is present
  • Translocation: a piece of a chromosome has broken off and reattached to another chromosome
  • Inversion: a piece of a chromosome has broken off in two places, flipped upside down, and reattached itself to the chromosome.

What Tests Look For Chromosome Changes? 

There are two common tests that look for chromosomes changes. The first is a karyotype. This is a picture of the chromosomes, similar to the first image on this page of a “Normal Female”. A karyotype can look for extra or missing chromosomes and large structural changes. The second test is a microarray.  This test does not provide a picture of the chromosomes, but uses other methods to look for very tiny extra (duplications) or missing (deletions) pieces of chromosomes. These tests do not look for changes in genes.

How is a Chromosome Change Diagnosed? 

Testing for chromosome changes may be offered to children who have concerns of early growth and development, such as failure to thrive,  developmental delay, birth defects, changes in appearance (dysmorphic features), cognitive delays, among other reasons.  An evaluation in a Genetics Clinic can help determine if chromosome testing is appropriate for a child.  Children can be referred to a Genetics Clinic by their family doctor or pediatrician.  The family will typically meet with a genetic counsellor and a medical doctor called a geneticist.  These individuals will gather information about family history (when available), the child’s medical history, and perform a physical exam that usually involves observing subtle differences in the appearance of a child.  The genetic counsellor and geneticist will determine what tests are appropriate to offer and will explain the advantages and disadvantages of testing to the parents and child (if appropriate) to help them make an informed decision about testing.  

Parenting a Child with Chromosomal Changes

Parenting a child with chromosomal changes can be challenging and rewarding. As a parent it is important to gain an understanding of what a chromosomal change means specifically for a child; as there are many possible diagnosis’s. There is no one set level of need and it can vary from some learning needs to significant mobility issues. Find out what the chromosomal change means specifically for the child. 

Since there are many different types of chromosome changes, it is important to gather information about the child’s specific chromosome change to learn how to manage their medical needs and how to best support the child to help them reach their full potential.

Learning about the child’s everyday functions, abilities, needs and services will assist you in determining if you are able to provide suitable care for the child. The worker and foster parent may be able to provide you with important medical history information including assessments that have already been completed. Knowing what has already been completed and having insight into what may already be working for the child will help you find the right tools, techniques and resources for a child.  

Helpful Links and Resources for Chromosomal Needs:

The Down Syndrome Association of Ontario - 

Unique: The Rare Chromosome Disorder Support Group -

The March of Dimes -

For a list of Genetics Clinics in Ontario, please visit:

The Canadian Association of Genetic Counsellors -


D. Hull, personal communication, May 8, 2014.

Greenwood Genetic Centre. (n.d).  Retrieved from -

National Human Genome Research Institute.  (n.d). Retrieved from -