sex-linked gene for height?

Factual Questions
1

It seems that in some families, the women are all short or average, while the men are all very tall. I’m talking mainly about siblings. When I say “short” or “tall” I mean in relation to the average height for that gender.
I’ve seen many instances within families where the men are all REALLY TALL and the women are all average.

In other families, members are randomly tall or short, relative to the average, regardless of gender.

My own family, while being too small to constitute a good sample seems to be of the “random assortment” type. My sister is only slightly taller than my short mother, and I’m taller than my father, which makes me tall for a woman.

I always thought traits like height and physical physique were inherited from both parents. Would “independent assortment” be the right term for that?

What could explain height/gender differences in some families and not others?

2

I have always heard that a son will be at least as tall as his mother. Sounds like there is some sort of sex linkage there. Course, I have nothing to back that up with.

3

That effect might exist, but it would be hard to demonstrate.

First, even if child heights are random (allowing for gender averages), we’d expect to see some sets of kids matching their same-gender parent, and might be biased into noticing those. The small families common today would also tend to hide any randomness. Does that single child matching their parent count, or is it just luck?

Second, height is determined by a lot of factors, both genetic and environmental, so connecting the effect to a genetic cause would be tough. We’d have to account for variation in diet, exercise, and disease exposure at least.

Now I’ll stop so somebody who knows what they’re talking about can get in.

4

Taller mommies tend have taller kids, because they’ve got those big, long wombs the kids can really stretch out in. Taller kids born to short mommies will tend to have back problems later in life because of the cramped quarters.

…What?

5

Height is a multifactorial trait. It is governed by the effects of many different genes, each of which may have several different forms, or alleles.

The expression of these genes may be different in the two sexes, in part due to the effect of sex hormones in during development. For example, a male will be taller than a female with exactly the same genetic makeup in terms of the genes that affect height.

It is possible that some of these genes are relatively more influenced by testosterone than others. That is, they may have a great effect on height in males, where a greater amount of testerone is present, while having little or no effect in females.

6

To paraphrase from an older and simpler genetics site (see http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgeninteract.html)

Height and a number of other human chacteristics are polygenetic…in other words, there are more than one pair of genes controlling the factor.

But to quote for another site (see http://www.abc.net.au/science/news/health/HealthRepublish_363100.htm)

"Over 4cm of men’s height is due to the combination of just two genes, according to a new study undertaken at the University of Melbourne.

The research, published in the Journal of Clinical Endocrinology and Metabolism this week, identifies one gene on chromosome 15 and one on the Y chromosome as contributors to height in men. These genes may also help explain why men are taller than women.

The genes operate independently but have an additive effect, said Dr Justine Ellis, who authored the study with colleagues Professor Stephen Harrap and Dr Margaret Stebbing from the Department of Physiology at the University of Melbourne.

“If you have the tall version of both of these genes you will be taller than a person who only has the tall version of one of them,” she said.

The Y chromosome is the male sex chromosome, absent in women. The gene on chromosome 15, called CYP19, codes for aromatase - an enzyme that converts testosterone into oestrogen in both sexes. Oestrogen influences height because it is responsible for bones fusing over at the ends, which stops people growing.

Aromatase seems to have its effect mainly on long bones, like those in the legs, said Dr Ellis. Men and women generally have similar-sized bodies, but men tend to have longer legs.

“That’s why there is a difference in height between men and women - because the legs are so important in determining height,” she explained.

A person’s height depends on both genetic and environmental influences. Previous studies have identified the aromatase gene and the Y chromosome gene as height genes in men who are very tall or very short, but the Melbourne study shows they also help determine normal adult height in the general population.

“We didn’t recruit people on the basis of their height in any way,” said Dr Ellis.

The aromatase gene accounted for 2.0cm in height, but the difference between genetically different individuals was much stronger in men (2.3cm) than in women (0.2cm), the researchers found. Variability in the Y chromosome accounted for 1.9cm.

“We have tracked down a couple of genetic components which together determine about 4cm of height in males,” Dr Ellis said.

The next step is to look at whether tall men have lower bone density, which may put them at risk of osteoporosis.

“One of the outcomes of work in this area is the design of drugs which encourage aromatase,” said Dr Ellis. Such drugs could assist people who have a mutation in the aromatase gene, so cannot make oestrogen in large amounts. This leads to long, thin bones that are vulnerable to fracture.

“In this next study we want to look at the more extreme height difference,” said Dr Ellis.

Her team would work with medical researchers who are bone specialists in the next stage of the research, she said. The team will include Associate Professor Ego Seeman from Austin & Repatriation Medical Centre and Associate Professor Peter Ebeling from Royal Melbourne Hospital.