About K Shows Expertise I am able to answer questions regarding human medical genetics, mouse genetic studies, molecular biology, biochemistry, and cell biology. I am also able to answer questions concerning prenatal and postnatal genetic testing but am ethically unable to give advice on such test results.
Experience I have 10 years experience in human genetics, including clinical, population, and molecular genetics. I am currently an active researcher in molecular and developmental genetics at Virginia Commonwealth University/ Medical College of Virginia. I have previously taught genetics and cell biology at the college level.
Organizations American Association for the Advancement of Science (AAAS)
American Society of Human Genetics
Education/Credentials B.S., Biochemistry, University of Southern Mississippi
M.S., Human Genetics, Louisiana State University Medical Center
Ph.D., Genetics and Vision Science, University of Alabama at Birmingham
Wow, thanks for such an informatiive and thorough response. Your answer made a lot of sense to me and I finally am beginning to understand how that is possible. So, thank you again. K shows, I want to ask three quick additional questions. I know we are all busy, so if you can only give short responses, that would be fine. But I would love to hear from you. You gave an example.
"if a person has the gene for short facial muscles that cause cheek dimples but also inherits a gene for a small face, then the short muscles would then be proportional to the small face and then the dimples would not show"
And you said.
"We know that several environmental factors can influence the growth of the face, as well as several different gene products that are only around during the facial development (the face develops during the first and second months of the life of the embryo, before many women know they are pregnant).
1st question : So, to due with your example, there could be many other possible reasons why the facial dimples are not penetrated but it may show up in the next generations because of something happening in the first or second months of life in the embryo or environmental factors? So, the point of my question is, there are more reasons why the facial dimples genes may not be penetrated in addition to your example? Can you give one other example?
2nd question: You said perhaps facial dimples could represent a facial defect other than short muscles or a cleft chin. So, you mean that someone who has facial dimples maybe did not inherit the gene but has an underlying facial defect? Could the defect be serious or an indication of something else? Or, not serious?
Last question: K shows, I was curious to know how you knew this knowledge about facial dimples. Was it your education in school, research, or your experiences in seeing other people with facial dimples? Reason I ask is because I have done so much research on it and almost found nothing and when I received your response, it made so much sense, more than any research I did.
Thank you again K shows and I hope to hear from you!
Nicole
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Followup To
Question -
Hello K Shows,
Thank you for this opportunity to ask a question. I am very much anticipating your response because I have found almost nothing on this subject and everything I have found is not complete or not make a lot of sense.So, again, thank you for this service.
I know so many people with facial dimples whose parents do not have facial dimples. I do not know how this is possible. Knowing that facial dimples is a dominant trait. For example, my sister in law has deep facial dimples and
only her great grandma had them in her family. So, is it because of variable penetrance, someone could be a carrier but does not show because of other factors? Or, perhaps it is a spontaneous mutation, knowing that dimples is a very minor defect? Professor, if you could give me some insight to this question, that would be great. Hope to hear from you..!
Nicole Wijedasa
Answer -
Nicole,
I think that the dimples trait is inherited as a tendency toward dimples, so that penetrance is not 100%. Cheek dimples occur when the muscles underneath the surface of the skin are shorter than the skin on top, so when you smile, the muscle pulls the skin at its attachment point, thus folding the top skin as it is pulled back. Chin dimples are actually a cleft chin in which the bones do not fuse completely (to form the face, the bony plates grow from the outsides to meet in the middle to form the mouth and lower part of the nose) and the outer skin lies on top of the cleft bone, revealing the structure underneath.
If you inherit the genes for dimples, that is, genes for short facial muscles or cleft chin, there may be other factors during your development that could lengthen the muscles, or allow full closure of the cleft chin. We know that several environmental factors can influence the growth of the face, as well as several different gene products that are only around during the facial development (the face develops during the first and second months of the life of the embryo, before many women know they are pregnant). In fact, sometimes dimples can be a marker for an underlying facial defect other than short muscles or cleft chin.
So, if dimples seem to skip generations in a family, it is probably due to reduced penetrance rather than new mutations. You are right: some people could be carriers and not show dimples because other factors "make up for" the short muscles or cleft chin that cause the dimples. For example, if a person has the gene for short facial muscles that cause cheek dimples but also inherits a gene for a small face, then the short muscles would then be proportional to the small face and then the dimples would not show.
I hope that this answers your question.
Answer Nicole,
To answer your first question, there are many factors that go into making an embryo "normal", most of it being the sequence of genes that are turned on so that the proteins are made in the correct proportions. There is a sort of circular balance of all of the gene products that participate in development and even in normal cellular processes. That is, for development (or other processes) to occur, there has to be the correct amount of gene product-- not too much or too little-- to produce the structures in the growing embryo. There are factors that repress aspects of development until the rest of the embryo is large enough or developed enough to support the new structure. For example, the ear is one of the last structures of the face to develop because it arises from tissue that begins below the lower jaw and migrates into position-- the friction of the movement causes the outer ear to be formed as it is rotated into place. If the genes that develop the ear are turned on too early, then the ear forms prematurely and stays below the lower jaw. If the genes that form the ear turn on too late, then there may not be an outer ear.
Specifically, a way that dimples could be "silenced" is if the facial bones are not rotated or completely formed, or if the shorter muscle somehow attaches to thebone at a different place. In addition, a person could have more fat deposits within their skin that would "fill" the dimples.
To answer your second question, I was referring to dimples in other places. Dimples that can mark an underlying condition can show degeneration of structure underneath the surface, for example, if a dimple appears in a place where there once was none. Shoulder dimples are the result of extra attachments of muscles to the bone underneath, which may signal a minor defect in movement ability. Sacral dimples, where the spine ends in the "tailbone", are an indication that the spine may not have fused properly. The defect can be serious, such as signifying a cancerous lesion, or totally benign like facial and chin dimples.
For your last question, I do work on a disease that is specifically involved in facial development. So I do know a lot of the information off hand; however, I did look up some information online to check my facts. Because I use the web everyday for my work, I am familiar with many science-based and medical sites that may be intimidating to non-scientists. Part of my job is to sift through information and make judgements on what is valuable and what is not. In addition, because I study facial development, I can read "between the lines" in the web information and use what I know about genetics to explain these things in more simple terms. The web is full of either very general or very specific knowledge, but not much in-between.
As far as the examples go, these are based on my knowledge of genetics and development, and my imagination of how these things work together-- they are not actual clinic cases. The more I study genetics, the more I realize that anything is possible, and it is a wonder that any of us are born "normal".
