What is the role of inheritance in the formation of twins?

Question

What is the role of inheritance in the formation of twins?

Answer 1

Having twins is genetic. I think "genetic" is more appropriate and accurate than "inheritance".

It means you need the genes to bear twins to have twins.

Answer 2

The role would depend on whether the twins were fraternal or identical.  

If the twins were identical, they would have formed from one egg which split soon after fertilization and would share the same genetic makeup (hence the "identical"-ness).

If the twins were fraternal, they wouldn't inherit exactly same traits.  If you remember back to Punnett squares, when a cross was done, you could get up to three different combinations of alleles, depending on what alleles the parents had:

   |_A_|_a_|

A|___|___|    = 1AA, 2Aa, 1aa

a|___|___|

And that's just showing one trait.  Given that humans have 23 pairs of chromosomes, there are 2 to the 23 power (2^23), or 8,388,608 possible ways for the chromosomes to pair.  And that doesn't even begin to consider things like crossing over which could provide additional combinations.

So as the gametes were produced and the two different eggs were fertilized, the'd be a much bigger chance that the traits could be different in each child in a set of fraternal twins.

Answer 3

Very little, but some.  Only hyper ovulation has any support as an inheritable trait promoting the birth of twins - and this only applies to fraternal twins.  Identical twins are random - if there is any heritability, it's too small to have been measured in the past.

(Inheritance is just as good a term as genetic.)