Have you ever wondered what makes you so similar to your parents? How much do you know about your family tree? Ever had health related problems running in the family? Which of those problems did your grandfather or father have? What if you pass it to your children?
Medical genetics has the answers to all these questions. It has also provided tools to understand how much of a certain disease and its risks can be passed on from one generation to another.
But, to understand how this works, one has to know what we call a genome—a set of genes (similar to a software) designed to operate an organism.
In humans, these building blocks (genetic code) make up our DNA and affect how we look and function.
Each gene can be equated with a recipe from a cookbook. Some genes give us curly hair or brown eyes while others help us process food and carry out daily body functions.
These genes are neatly packaged to form structures called chromosomes. One human cell has a total of 46 chromosomes arranged as 23 pairs. They include sex chromosomes X and Y. One member of every pair is inherited from each parent during conception.
Facts you must know
Humans typically share 99.9 percent of their DNA. The 0.1 percent is what makes them different! Females do not possess the Y chromosome; this means the father’s contribution from the sperm cell (X or Y chromosome) determines the gender of the child.
A better understanding of the concepts relating to this aspect of genetics is detailed in the human genome project (HGP), an international research collaboration to determine and study the blueprint of life, DNA.
It began in 1990 and was completed in 2003 and so far it has enabled a better understanding of diseases in the field of medicine, biotechnology and life sciences.
Yes, the human genome is quite large. To put it to perspective, it would require over 140 large phone books to print the entire genetic code. In other words, the length of human DNA is equivalent to nearly 70 trips from the earth to the sun and back!
When things go terribly wrong
Errors (also known as mutations) in the genetic code mean there is a problem in the recipe book we talked about earlier.
With an incorrect recipe; things can go terribly wrong. These problems can happen in two major ways; either inherited from parents or acquired from environmental factors such as over exposure to the UV radiation from the sun and many more.
Remember, for proper functioning of genes and therefore proper functioning of the human being, the correct sequential arrangement of the building blocks (making up the DNA) is very crucial.
Diseases caused by genetic defects
Genetic diseases can occur in various scenarios. For some diseases, a single change in one building block, in one gene, is enough to cause problems.
While, for other diseases, it would require multiple errors in multiple genes to cause severe problems.
Examples of diseases caused by genetic defects include: (Single gene genetic inheritance) Cystic fibrosis, Sickle cell anaemia, Huntington’s disease, Colour blindness.
(Multiple gene genetic inheritance) Breast cancer, Heart disease, Alzheimer’s disease, Parkinson’s disease, Diabetes, Arthritis, other cancers.
Others occur due to abnormal chromosomes. They include Down’s syndrome, Turner syndrome, Klinefelter syndrome, Cri du chat syndrome.
Genetic testing can be used to do early screening to find if a woman has mutations in genes that can cause breast cancer and therefore allow immediate interventions to prevent cancer from spreading before the symptoms even occur.
In addition, genetic testing can be used to screen for any mutations from the DNA of an unborn child to allow early detection of any deadly genetic disorders.
Currently, over 1000 genetic tests are in use and more are being developed.
“Genetic testing is voluntary. Because testing has benefits as well as limitations and risks, the decision about whether to be tested is a personal and complex one. A geneticist or genetic counsellor can help by providing information about the pros and cons of the test and discussing the social and emotional aspects of testing.” This is according to the Genetics Home Reference.
Note that genetic testing can be done on blood, saliva, bone marrow, muscle, amniotic fluid or other tissue. It can be done at any time as genetic information does not change over time. Costs can vary between less than $100 to $5000 depending on the investigation carried out.
Genetics, in particular, the application of genetic testing, has opened a new door for the medical field known as Genomic medicine, that promises improved diagnostics and therapy as the future of medicine. Check out the next week’s column to read about ‘’making sense of your genes’’ and more about genomic medicine.
The author is a trained Molecular Biologist and Biotechnologist currently pursuing a PhD in medical genetics in The Netherlands.