Inheriting a ghost chromosome.

By Peter Dearden 11/03/2015

Peter K. Dearden

Today and yesterday I have been a meeting in Auckland, called by Prof Sir Peter Gluckman, to discuss the importance of non-genomic inheritance.  It all sounds rather flash, but good science can be done in discussion with interested experts. Sometimes at these events you might see something that you missed.

One of the overseas people at this meeting was Prof Jo Nadeau, a geneticist of note from Seattle. He talked about some cool experiments that were carried out in his lab using mice to examine various aspects of genetics. One of the experiments he talked about was published a few years back. I missed it at the time but it is remarkable so I though I might write about it.

Our understanding of genetics is that DNA is the molecule of inheritance. We get half our DNA from our mother, half from our father, and it is the combination of those DNA molecules that produce our own trails.  The sequence of DNA carries that genetic information and influences our particular biology.

Mendel, the discoverer of the laws of inheritance, recognised the patterns in the inheritance of traits, and our later understanding of chromosomes and DNA explained how our DNA is recombined and passed to our offspring.

What is surprising is that in Nadeau’s work, the genetics of the father (in this case a mouse) can influence its offspring without the transmission of DNA.

In mammals (such as mice and ourselves) there are the normal set of chromosomes (autosomes) and then the sex chromosomes. The sex chromosomes, named X and Y, help determine biological sex. Individuals with two X chromosomes are female, those with XY are male. The inheritance patterns of these chromosomes are a little different because the Y chromosome pairs with the X.

We have two copies of each chromosome, but when we make sperm or eggs, only one copy is packaged into each sperm or egg.

So females (XX), can only make eggs that carry an X. Males (XY) can make sperm that either carries an X, or a Y (not both). You can be XX, or you can be XY, but not YY. So if you inherit a Y chromosome, you will be male, and you got the Y from your dad. If you are female, you inherited one of your mother’s X chromosomes, and your dad’s ONLY X chromosome.

It all sounds complex, but here all you need to know is that daughters do not inherit their dad’s Y chromosome. Because of this, there should be no effect of the sequence of dad’s Y chromosome on daughters. They don’t get the DNA, they shouldn’t have any sign of an influence of their dad’s Y.

In this case the researchers, using mice, looked to see if anything about the biology of daughters could be correlated with the Y chromosomes their father had. If they weren’t looking at the Y chromosome you would expect to see evidence that the dad’s DNA affected their daughters. But the researchers found the same effects for DNA sequences on the Y chromosome. The dad’s Y chromosome, despite not being inherited by daughters, was still having an effect, especially on anxiety.

This is remarkable, but is being reported more and more. Inheritance of some traits without DNA implies that there are some mechanisms (in this cases carried in sperm) to transfer information between generations without DNA.  We wait with baited breath to understand what those mechanisms might be.

Now this is all complex mouse genetics, and we, as yet, have no idea if it occurs in other species. It sort of makes sense from an evolutionary point of view in that it might be an advantage for males to pass information to their daughters in this way. It is vital, however, that we begin to understand the consequences of this kind of inheritance for genetics, evolution and human health.

If you are female, whatever else your father may have given to you, he may have bequeathed you the ghost of his Y chromosome.