Frequently Asked Questions

Question: Do you have any resources for twins who have lost their twin? 

Yes, please see this link

Question: Do you have any resources for twins who don't get along with each other?

Yes, please see this link

Question: What research is occuring around the world using twins - is there a book I can get to give me a "Crash Course in Twin Research"?

Erm... that is a huge question! This link should help 

Question: Can Identicals ever be Boy/Girl Twins?

Logically, one would imagine that identical twins by default are the same sex, yet researchers have shown that in some rare cases, identical twins from an egg and sperm which began as male (XY) can actually develop into a male / female pair due to a genetic mishap occuring when the egg divides.  This happens when the fertilised egg 'looses' one of the copies of the Y chromosome when it is dividing into two embryos in very early development. The resulting babies are then male (XY) and female (XO). The normal genetic make-up of a girl is XX. An XO baby is outwardly a girl, but her cells only have one copy of the X chromosome, not two. This condition is called Turner Syndrome.

For more information on this, see the following links:

BellaOnline

Turner Syndrome

Question: Can fraternal twins look so similar that they are mistaken for identical?

Yes! Fraternal twins can look remarkably similar! Here is a quick rundown of genetics to help explain this:

The body is made up of millions of cells.

Each body cell has copy of 46 chromosomes.

The 46 chromosomes are actually 2 complete sets of 22 non-sex chromosomes and 1 sex chromosome (commonly called the X or the Y chromosome)

Each ‘set’ of chromosomes has been inherited – one set from Mum’s egg; one set from Dad’s sperm. Imagine that this is like having 2 suits of cards – one red; one black. You would have one red King; one black King; one red Queen; one black Queen. Imagine that the sex chromosomes are like the 2 jokers stuck on the end.

Sex cells (eggs and sperm) only have one set of chromosomes – this is so that when an egg and sperm come together; they merge; providing one ‘set‘ each; and the new cell that results (and ultimately grows into the foetus) has the correct number - 2 sets.

Sub - Question: Hang on! So what exactly are chromosomes?

Chromosomes can also be thought of as similar to a ball of wool - if you were to unravel the chromosome; like you would unravel a ball of wool; you would find long lengths of DNA – this is like the ‘thread’ of the ball of wool.

Sections of DNA make up genes

Genes are basically recipes for creating every function of the body; including looks; and as some researchers have found; personality and behaviour.

Because each person has 2 sets of chromosomes; that means they have 2 recipes for every gene (like having 2 slightly different recipes for the same type of chocolate cake). Usually; one version is stronger or more ‘dominant’ than the other and so that copy is seen or ‘expressed’ in the person. For example; take the gene for eye colour: the brown version is stronger than the blue version of this particular gene. So if a person inherited one blue version of the gene in the set of chromosomes they got from their Mum’s egg; and a brown version from their Dad’s sperm; they will have brown eyes. They will still have both versions in each of their cells but as the brown version is ‘dominant’; it is the one ‘expressed’. It is said that the person then ‘carries the gene’ or is a ‘carrier’ for blue eyes – they could still pass that blue eyed version of the gene onto their own kids; but they won’t ‘express’ it themselves.

When an egg or a sperm is formed in a parent; the chromosomes are shuffled around. Just like the red and black suits of cards getting mixed up. Not only that; the pairs of chromosomes actually ‘cross’ each other. This is like taking the red King and the black King; cutting them in exactly the same place through the centre and sticking the opposite parts together. Therefore; on one chromosome; the top section has the genes that were on the red set; the bottom section has the genes that were on the black set and vice versa. This is why children show characteristics of both sides of their family. After all of this shuffling about and crossing over takes place; the cell splits down the middle; taking only one complete set of shuffled up chromosomes.

When all this shuffling and crossing and dividing takes place; effectively; you have a random assortment of red and black recipes in each sex cell. That’s why you can have siblings that look wildly different and ones that look startlingly alike – it all depends on how the genes and chromosomes are shuffled and what versions end up in each egg or sperm cell. In the case of fraternal twins; 2 eggs have been released by the Mum and each fertilised by 2 different sperm from the Dad – there’s always the chance that those eggs from the Mum had a very similar set of shuffled up chromosomes and the same with the sperm – meaning that the fraternal twins could actually look very similar. The opposite is also true – the eggs from the Mum and the sperm form the Dad could; just randomly; have a very different shuffled up sets of chromosomes; meaning that the fraternal twins could look hardly anything like each other. You may have seen that article on the news with the black and white twins? They are fraternal but are very different in skin colour. This is a perfect example of the random nature of sex cell creation. This shuffling only takes place during the creation of sex cells.

It’s also known that non-twin siblings can actually look very similar as they grow up; but because non-twins are at different ages at any one point in time; people don’t realise how similar they actually look. It’s only when you do something like putting their Grade 3 school photos side by side that you realise how similar they are!

In the case of identicals; as I’m sure you know; there is only 1 egg and 1 sperm; that fuse; and start replicating into a clump of identical cells. At some point in time; and for reasons still not yet well understood; this clump divides down the middle; and each clump forms a new foetus. Therefore they have exactly the same chromosome sets and genes.

Question: OK; so can identical twins ever look different?

Err; yes!

Even though I said above that identical twins are from the same sperm and egg; and therefore have exactly the same set of chromosomes and therefore genes; researchers are realising that there are other forces at play – the science of epigenetics.

Epigenetics basically says that just because 2 people have the same set of genes (like identicals); because of the different environments the experience – i.e. in the womb (maybe one got more nutrients than the other); the types of illnesses they have had as they grew up; the lifestyle they lead etc etc; that there can actually be differences in how much each twins genes are turned on or off – this can then affect the way each twin looks and behaves. This effect actually increases as the identical twins get older – because more and more environmental events happen that are different between each twin – different friends; illnesses; jobs; partners; habits etc.

There is another cause of differences in identicals which occurs in female identicals. When a female foetus is created; it has 2 copies of the X chromosome (one provided by Mum’s egg; one by Dad’s sperm; a boy has one X from Mum and a Y from Dad). I said above that generally the version of each gene that is ‘dominant’ is the one that is expressed – this is different for the X chromosome – this chromosome is unique in that one of the chromosomes is permanently ‘silenced’ very early in embryonic development so rather than gene ‘expression’ working from whichever version is ‘dominant’ as I mentioned above; the only genes that work are the ones on the X chromosome that is not ‘silenced’. This silencing can happen AFTER the identical twins have been created and are developing (when the embryo has grown to about 10-20 cells); and if by chance one identical twin ‘silences’ the X chromosome that came from Dad’s sperm; and the other twin silences the X chromosome that came from Mum’s egg; then effectively; they will have different genes working in their systems; which can result in noticeable differences. The X chromosome has about 120 different genes; so the effects of each twin silencing a different X chromosome can be quite obvious.