What Little I Understand About Genetics

Litter-mates are not twins. Identical twins have exactly the same genetic complement, coming from a division of the original single fertilized egg, each half of which goes on to become a separate organism. This is apparently something of an anomaly, as identical twins are a rarity.

Litter-mates, on the other hand, are sisters: products of the same gene pool--that is, distinct combinations of the genes of the same father and the same mother--but not the exact same combination of those genes. Puppies from the same litter would be, in human terms, fraternal twins (as opposed to the identical twins cited above); as I understand it, fraternal twins involve distinct, different eggs which are fertilized simultaneously from among the father's (billions of) sperm. This is all covered in greater detail here.

This business interests me because the two girls are so similar in so many ways--strangers inevitably cannot tell them apart except by collar color--and yet they have quite distinctive personalities and talents. Snickers, the larger of the two, is boorish and dominant. Bella is smaller and more wily, often outsmarting Snickers. Bella figured out how to jump out of her potty pen outside, while Snickers looked on in wonder, unable to duplicate the feat (a month later Snickers still cannot get out of the pen). Bella has made much more progress in her potty training (though neither is ready for graduation), and she is beginning to figure out how to deal with stairs. Snickers seems blithely unaware of any of this, looking instead for Bella's next snack which can be easily taken away from her.

And littler things: Snickers will gobble down her heartworm medicine, and Bella simply cannot be enticed to do it. And once she figures out that we want her to eat something, then it's out of the question. I've tried peanut butter, corned beef, even tuna--Bella will have nothing to do with it, though Snickers is ready to break down walls to get to the feast. When we go for a walk on our leash, the two girls behave differently, but in a repeated, predictable, interlocking way--kind of like yin & yang.

So how much is each responsible for what the other is becoming? What role has Snickers's boorishness played in Bella's intellect? How has it affected Snickers to have a submissive sibling always underfoot?

It all raises so many questions about

nature versus nurture
A traditional and long-standing disagreement over whether heredity or environment is more important in the development of living things, especially human beings.

www.answers.com/topic/nature-nurture-controversy