The coding order of that DNA makes up the genes. If one of the pairs of genes is missing or damaged the other matching gene is unable to make up for the deficiency. Some characteristics only require one gene to work correctly out of the pair that are available - these are Recessive genes . Generally, for a child to have a recessive disorder, both parents must 'carry' a missing or damaged gene and pass both these on to their child. A third type of inheritance pattern occurs due to one of the chromosomes that define our gender, the X-chromosome.
Males only have one X-chromosome, whereas females have two.
It is possible for a genetic counsellor to gauge what the inheritance pattern is just by asking about your present and past family members to see if there were other cases. It is important to note that most chromosome abnormalities occur as a accident in the egg or sperm. In this case the fertilised egg or sperm multiplies and therefore every cell in the body has the abnormality. Genetic Testing Testing for a particular condition will first start with a clinical assessment to try to ascertain what the suspected condition or the range of conditions might be. An MRI or CT scan will be used to help provide the clues to what to do next.