How Do Conjoined Twins Have Different Personalities?

[predictability]

The question of 'why and how do conjoined twins have different personalities' popped up in my mind while I was studying a mostly unrelated topic. They have the same nature (genetically speaking they have 100% same DNA) and almost same nurture (what one experiences the other most likely will as well e.g. medicine)

 

Then a hypothetical experiment came to my mind following the question. If you plant two genetically identical seeds of a tree into the absolutely same environment (same soil, same water, same light, same everything), when the tree grows from the seed do the branches branch out absolutely the same way?

 

Can anyone tell me the answer to these two questions (a theory would be nice too)? Thanks in advance!

[joekgamer]

For the question about the tree seeds, presumably they would. Most plants grow towards the sun, and so under the same conditions, the same thing would happen.

 

However, with the question about twins, while they may have the same DNA, that doesn't necessarily mean that they have the same personality. If they were to grow up in exactly the same environment, then it would be likely that they would have the same personalities. However, if even one thing is different early in life, then that could butterfly into a huge difference. Essentially, same conditions means same results. However, twins don't necessarily get the same environment, even if they live in the same house. If one breaks their arm, then the same doesn't automatically happen to the other. While that example is a rather severe one, the principle is the same even all the way down to the TV programs that are on at the time that they start watching TV.

[JMJones0424]

If you plant two genetically identical seeds of a tree into the absolutely same environment (same soil, same water, same light, same everything), when the tree grows from the seed do the branches branch out absolutely the same way?

 

Absolutely not. This is easier to demonstrate if instead of propagation from seed, you use cuttings. I work at a nursery where we plant thousands of cuttings from the same mother stock. Every cutting is treated the same from rooting until it is sold. All cuttings from the same stock will be genetically identical and exhibit the same basic genetic traits. However, even though each cutting undergoes the exact same treatment, there is still so much variation in growth patterns that on average 20% of each variety will not meet our standards for sale for various reasons.

 

It helps to imagine DNA as being more like a recipe for baking a marble cake rather than a blueprint for a building. If you follow the recipe, then all marble cakes will essentially be the same (genotype), but there will be differences in the shapes of the swirls (phenotype) because the recipe alone is not the only thing that determines the final product.