Dominance and Birth Defects – Making Sense of the Alphabet Soup

If you have ever sat through the average upper level high school biology class, you were sooner or later treated to Gregor Mendel and his pea plants. Father Mendel was a priest who in his spare time enjoyed a bit of gardening and eventually noticed that the color presentation of certain plants appeared to follow a predictable pattern. Working more on his theories of the inheritance of traits, he soon developed the theory of dominant and recessive genes. Unfortunately, he was made an abbot and as such no longer had the time to devote to his experiments. In addition to the foregoing, scientists of the time, including theorists like Charles Darwin, considered his scientific findings worthless and it was not until several decades later that his findings were able to be reproduced, thus indeed showcasing that he was correct all along in his findings that certain dominant genes will elicit certain traits to evidenced in a plant or animal.

From there it was only a small step to apply the theory of dominant genes to the human body. Modern science has connected genetic dominance and birth defects via a veritable alphabet soup of markers and abbreviations that sometimes makes it hard to understand just what is being said. In order to make some sense out of all the abbreviations, here is the relationship between dominance and birth defects in a nutshell:

1. Dominance of a genetic trait simply means that you will see it brought to expression in the appearance of a body when it is pitted against another but recessive gene.

2. An easy to understand example is the color of the iris which determines your eye color. Brown is a dominant trait, an as such when genes with the brown coding are present, the child will have brown eyes. Conversely, if the dominant brown trait is absent, the next most dominant gene, in this case green, will determine the color of the eyes. Green is a recessive gene, but when compared to other recessive genes determining eye color, it is almost always dominant.

3. Therefore, if a child receives a green recessive iris determining gene from his father, but a brow dominant iris determining gene from his mother, the odds are good that the child will have brown eyes.

4. Of course, this is highly simplified and is rarely, if ever, as simple. Dominance may sometimes refer to a condition where a conceived child will inherit identical dominant genes, while other times the dominant gene will be pitted against a different dominant gene. Then again, at times a dominant gene may be offset by a certain combination of recessive genes.

5. Birth defects that may be linked back to a dominant combination of genes are Huntington’s disease which has been located as a gene present on chromosome four, Pfeiffer syndrome, and also hereditary multiple exostoses which refers to bony masses that form and attach themselves to the various bones in the body of a child. There are a host of other diseases associated with the dominant gene, and many of these will be diagnosed successfully during genetic counseling prior to conception.

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