Genetics and Height
What inheritance pattern does height follow? I think it is
Polygenic, if so could you tell me why?
Actually, height is what is called multifactorial. Not only are there many
genes involved, such as genes for growth hormone, genes for the receptors on
the outside of cells for growth hormone, genes for bone proportion, genes
for the timing of the release of hormone and other growth factors; but there
are also many interactions with the environment, including nutrition during
gestation (while the mother was pregnant) and during the growth years,
exposure to things such as cigarette smoke and alcohol before birth, birth
order (generally second children are taller than first) and general health
during the growth years. With all of these factors, it appears that we are
born with a genetic potential for height (not all of the genes have been
identified yet) and then the environment exerts its effects as we are
Incidentally, I'm an adult woman who is 4 feet, 11 inches tall. My sons are
5 feet 8 inches and 5 feet 10 inches tall. Their father is 5 feet 9 inches
tall. My children both exceeded what a children's growth specialist
predicted for them when they were very young, and no one knows why!
If height were controlled by a single gene and tall were dominant, then only
two heights would be possible, tall and short. Even if height were
incompletely dominant, in other words, being heterozygous blended the two
other phenotypes, only tall, medium and short would be possible. This
obviously isn't right. Height is under the control of more than one gene,
perhaps many. It depends on how many active alleles you inherit from your
parents. Lets say that height is controlled by 3 genes each with 2 alleles.
So there are 6 possible active alleles, or alleles that actually contribute
to height. Lets say that your father is medium tall or has 4 active alleles
and two inactive. Lets say mom is medium and has 3 active and 3 inactive.
Their children can have as many as 6 active alleles ( 3 from each) and be
very tall. Or they can inherit as few as 5 inactive alleles and be quite
short (although not as short as possible).
There is another factor to
consider though, height is also a multi factorial trait-the environment has a
role in determining your final height. Lets say that you were genetically
programmed to be tall but you didn't have access to good medical care, had a
poor diet and your mother smoked while she was pregnant. You may not reach
your possible height. Boys have testosterone which increases muscle mass and
bone growth more that estrogen does so boys usually are taller than girls.
So, height is a complicated genetic factor.
I think height of humans develops in such a complex
way that we do not understand all of it. As a rule of
thumb, a child will be the size of the average of the
parents, or slightly taller. But that may not be true
for individual cases.Both Nature and Norture have a
thing to say: both inheritance and other factors are
We know little about these other factors. People in
Northern Europe are taller than in Southern Europe.
Children in Northern Europe grow taller than their
parents, and this has been going on for generations.
The Dutch and Scandinavian people are now among the
tallest in the world. But why? A balanced diet,
healthy pregnancies, optimal medical child care, and
high social standards result in more height. But even
correcting for the absence of vitamin deficiencies and
crippling diseases from the past, it is hard to
explain why tweens are now few inches taller than the
tweens of 20 years ago.
I don't know whether this is observed in other parts
of the world as well. A Dutchman visiting Asia feels
like a giant. My guess is that the genes dictate that
this won't change in future.
Dr. Trudy Wassenaar (Dutch)
It is polygenic...we are fairly sure of this because of the inheritance
patterns it follows...that is they are do not follow what would be typical
from a single gene.
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Update: June 2012