DNA Day experts answer your questions about heredity and physical traits

CurioCity
30 April 2013

Above: Image © Ygraph.com, Wikimedia Commons

What determines premature balding? Is it from the father's or mother's side?

I'm no expert on this specifically, but there are multiple underlying causes of balding (a.k.a. alopecia). The best current guess is that the most common form is about 25% determined by genetics with no particularly strong influence of sex.

- Answer provided by Dr. Paul Gordon

If guys do not have facial hair, is that hereditary?

That is a very interesting question. Often times phenotypic (outward) traits like hair growth, eye color, skin color and other similar facial features are controlled by a number of different genes. This can make it complex and difficult to pin point exactly which gene may cause that trait, but hair growth (including facial hair) does has a genetic component to it. How much of this hair growth is affected by genes is again hard to determine. So if a male has less facial growth, it could very well be a genetic inheritance, in which case his father, and males from his father family (or even males from the mother's family), may also show traits of less facial hair growth. However, this is again hard to determine without a full family history of the person in question. There could also be other possible reasons for less facial growth. For example, if the male is relatively young, he may been late in getting puberty and the physical and hormonal changes that come along with that change such as facial hair growth. Expanding on the hormonal aspect, there are certain hormones like testosterone that help develop male secondary sex characteristics like facial hair growth. So if, due to a medical reason perhaps, the person has low levels of testosterone, then that could also lead to less facial hair growth as well (which would not necessarily be a genetic reason). Hope that helped!

- Answer provided by Harman Sawhney

How is eye colour inherited? Why do some people have eye colours that change?

While there are some genes that determine brown or blue eyes, and the brown is thought to be dominant and the blue recessive, there are actually other genes, and single nucleotide replacements in these can shift pigmentation around significantly - so it's not simple.

- Answer provided by Jay Ingram

My friend's husband is black with brown eyes from Haiti and both his parents are black, and my friend is white with blue eyes. Their two children are both very pale with blue eyes. Does this automatically mean that the father is carrying the recessive blue gene?

If your friend is homozygous recessive for an eye color gene and your friend's husband is heterozygous for the same gene, both parents could contribute a copy of the recessive gene to have a blue-eyed child. So yes, it is possible that your friend's husband is carrying a copy of the recessive blue gene. However, research has found that human eye color is determined by multiple genes on different chromosomes and events such as gene mutation and gene activation/inactivation may also be occurring, so we don't know for sure. Here is an article I found through the CurioCity site that further explains eye color heritability: http://www.cosmosmagazine.com/news/eye-colour-more-complex-we-thought/ . I hope this answers your question.

- Answer provided by Caleyr1

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