Having only done basic genetics, I’m not entirely sure as to how they influence the way an induvidual’s face looks. Some people appear to be exact replicas of one parent, while others seem to have an even combination (I understand this has to do with dominant and recessive genes). However, I’ve also noticed noses or ears or chins that appear to be the result of combining both of the parents features. Sort of a facial version of 1 + 1 = 2, rather than either 1 overriding the other.
…if that makes any sense whatsoever.
Is it a sort co-dominance, like eye colour (if I remember correctly)?
As an aside, I have what appears to be a highly defined “lower” philtrum, in addition to the typical one. The philtrum is the two ridges running vertical between your nose and upper lip, and I have another set running from my lower lip to the beginning of my chin. I know the philtrum is formed where the nasomedial and maxillary processes meet during embryonic development (scientific words courtesy of wikipedia), but is there any reason for one to form beneath my bottom lip?. I’ve yet to notice anyone else with the same thing, apart from the small notches some people have directly under their lip. No one in my family (to my knowledge) has this. Did I have a distant great-granparent with a “lower” philtrum, or is there another biological explanation?
Thankyou for any answers in advance.
Most facial features are multifactorial, that is, they are determined by a the action of many genes acting in combination. They depend not just on which alleles you have for a single gene (which may show a dominance-recessive relationship, in which you can show one parental trait or the other, but not both; or co-dominance, in which the offspring’s traits are intermediate between those of the parents), but also by which alleles you have for a number of other genes (which may also have either dominant-recessive or co-dominant modes of inheritance).
Your chin shape, for example, may be determined by a combination of 5 genes, any of which may have multiple alleles, with inheritance of various types. Because of this, the exact result of given parental types can be impossible to predict.
Note that the most important eye color gene shows a dominance-recessive relationshop between the brown (dominant) and blue (recessive) alleles, not co-dominance. However, even eye color is multifactorial, and other genes besides the brown-blue one are also involved, producing green, hazel, etc variants.