Why Barbra Streisand's cloned dogs aren't identical to the original pet

Wouldn't it be wonderful if we could bring back a deceased loved one? Such ideas used to be pure science fiction, but recent advances in biotechnology seem to have brought this possibility within reach (at least for the wealthy). 

When American singer-actress Barbra Streisand lost her beloved dog Sammie last year, she decided to have her cloned. She's now raising Miss Scarlet and Miss Violet, both of whom are exact genetic replicas of Sammie. (You'll be glad to know that any pet owner can do the same: for a mere US$100,000 or so, you too could have a genetic replica of your favourite cat or dog.)

But Miss Scarlett and Miss Violet almost certainly won't turn out to be identical, mini versions of Sammie.

Popular culture is permeated by the belief that the features of a plant or animal (including a human being) are fully determined by its genes. Newspaper articles regularly announce the (often dubious) discovery of a "gene for" some physical feature or personality trait. So it's hardly surprising that the production of exact genetic replicas through cloning is seen as a way to recreate individuals with all their features intact. That's certainly how it works in the movies.

The reality is far more complicated. In a recent interview with Variety, Streisand noted that Miss Scarlet and Miss Violet "have different personalities" and "I'm waiting for them to get older so I can see if they have (Sammie's) brown eyes and her seriousness".

Streisand's observations are consistent with evidence that human identical twins (who also share all their genes) often diverge markedly in personality, health and even physical features.