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Explaining inheritance

How do I explain how a condition is inherited?

DNA, genes, chromosomes and inheritance – these are terms often found in media stories highlighting their role in genetic conditions. Your patient may therefore ask you how alterations in these might explain their genetic condition, if specific treatment is available, or whether there might be implications for their family.

In the video below, renal genetic nurse specialist Kathryn Bishop discusses the value of understanding modes of inheritance, and how such knowledge can help staff to support patients.

 

This section currently contains resources we have developed to help you explain some of the modes of inheritance to patients, or help them visualise the physical basis of chromosomal conditions. Future plans include tips on how to explain the effects of alterations in genes and DNA in causing genetic conditions.

But before using our clinical resources to give information:

We have listed our current resources under the three common types of inheritance, single gene, chromosomal, and multifactorial.

Single gene inheritance – autosomal and X-linked dominant and recessive inheritance

For single gene conditions, it is usually known how the condition is inherited: the probability that someone will inherit or be a carrier for the condition can therefore be explained using the rules of that form of inheritance. Clinical experience suggests that most patients find it helpful to understand how these “risks” (such as 1 in 2 or 1 in 4) have been calculated by visualising the inheritance of the genes involved from parent to child. Drawing a diagram and discussing it allows a health professional to show how different genetic combinations can occur in children depending on how genes are passed on from parent to child (through eggs and sperm).

Using and annotating a pre-drawn diagram during the consultation

Using a pre-drawn template can be helpful during a consultation to explain single gene inheritance. Our template shows one pair of chromosomes for each parent. Each chromosome has a single gene highlighted that can be coloured in to illustrate a gene alteration. You can then show which sperm and/or eggs contain the chromosome with the gene alteration and the different genetic combinations that could be present at conception.

Explaining autosomal inheritance

A PDF document

A template to help explain autosomal inheritance

Use this worksheet to explain autosomal inheritance.



Explaining sex chromosome inheritance

A PDF document

A template to help explain X-linked inheritance

Use this worksheet to explain X-linked inheritance.



Chromosomal conditions

For chromosomal conditions, using pictures of real chromosomes is often helpful for a patient to understand the physical basis of a chromosomal condition in the family.

We have prepared two worksheets showing what normal chromosomes look like down the microscope, and then how the laboratory arranges them in pairs to make it easier for scientists and doctors to detect any variations which might cause a chromosomal condition.

A PDF document

An example of the chromosome pattern of a male (46, XY karyotype)

Use this worksheet to show what normal chromosomes for a male look like down a microscope, and how the laboratory arranges them in pairs for easier detection of any variation.

A PDF document

An example of the chromosome pattern of a female (46, XX karyotype)

Use this worksheet to show what normal chromosomes for a female look like down a microscope, and how the laboratory arranges them in pairs for easier detection of any variation.

Many chromosomal anomalies occur as a “one off” event during the production of an egg or sperm – particularly those that result in an additional whole chromosome (such as the trisomy 21 type of Down syndrome).

We have also prepared some pictures of the chromosome patterns found in people with trisomy 21 Down syndrome, and Patau, Edwards, Turner and Klinefelter syndromes.

A PDF document

An example of the chromosome pattern of someone with Down syndrome (Trisomy 21)

Use this worksheet to show the chromosome pattern of someone with an extra chromosme 21 which results in Down syndrome (Trisomy 21).

A PDF document

An example of the chromosome pattern of someone with Patau syndrome (Trisomy 13)

Use this worksheet to show the chromosome pattern of someone with an extra chromosme 13 which results in Patau syndrome (Trisomy 13).

A PDF document

An example of the chromosome pattern of someone with Edwards' syndrome (Trisomy 18)

Use this worksheet to show the chromosome pattern of someone with an extra chromosme 18 which results in Edwards' syndrome (Trisomy 18).

A PDF document

An example of the chromosome pattern of someone with Turner syndrome

Use this worksheet to show the chromosome pattern of someone with Turner syndrome.

 

A PDF document

An example of the chromosome pattern of someone with Klinefelter syndrome

Use this worksheet to show the chromosome pattern of someone with Klinefelter syndrome.

 

Some chromosomal changes are more complicated, and in some cases can be inherited. Patients with these types of alterations are usually referred to the genetics services, particularly as it may be very important to offer chromosome testing to other family members. Often these types of changes are unique to an individual family, so the person explaining such changes often has to draw the pictures of the changes to the chromosomes freehand.

 

Common complex conditions

Multifactorial conditions are associated with a combination of environmental and many genetic factors acting together.

When we use the word “environmental” in an explanation with patients it may sound as though we know what the environmental influences are. In fact for many conditions the precise environmental influences involved have yet to be identified. Also some patients can feel guilty that their lifestyle or particular environmental events to which they were exposed may have led to a condition in a child, for instance.

Unlike single gene disorders where the probability of recurrence can be deduced from the rules of inheritance, the probability of a relative having the same common complex/multifactorial condition has to be a figure observed from clinical practice.

This usually means that a large study was undertaken to look at many families where a person had been diagnosed with the condition. The number of relatives in the family with the same condition was then counted. From these studies, the probability that a brother or sister, or aunt/uncle or other relative would have the condition was able to calculated. These figures have been published in individual research papers, but many have been collected together in books for use in clinical practice, such as Professor Peter Harper’s book Practical Genetic Counselling (7th edition, 2010).