Science Questions

Why are children all so different?

Tue, 14th Aug 2012

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Question

Cameron Lapworth asked:

Hi Chris,

 

Firstly Love the show. A question that has been bugging me thought it might be good for Question of the Week

 

I was wondering what mechanism causes children born to the same parents all have different characteristics from each other. I understand that half the Chromosomes come from the father and half the Mother so you'll always get a mixture of both parents characteristics. However, this simple understanding doesn't explain why they aren't all identical twins (albeit born at different times). So are the Chromosomes somehow jumbled further say chromosomes no. 2 from Mum and no. 4 from Dad? What mechanism controls individuality?

 

Ta Cameron Lapworth

Answer

Dr. Zegerman:: So to understand real individuality really have to understand how you and I were made. It really starts when a sperm from your dad and an egg from your mum got together and made you as an individual. Sperm and egg are made by a special form of cell division, which is called meiosis.

Meiosis is special because it turns a diploid, which has two copies of every chromosome, into a haploid, which has one copy of every chromosome. So, when cells goes through the process of meiosis, you take this 46 human chromosomes and you turn it to a cell with one copy of every chromosome, which now means has only 23 chromosomes.

And very importantly, this process of meiosis is random. Every cell that goes through meiosis will inherit one of every chromosome, but whether inherits one from your mother or father is random. So for example, when your fatherís cells went through meiosis to make sperm, it was random whether that you inherited chromosome 2 letís say, from his mother or chromosome 2 from his father.

So now, you can see that when you get an egg and a sperm fusing together, as happened for you and your brothers and sisters, you now see this is now a random collection of chromosomes that arenít just from your parents but random collection of chromosomes they inherited themselves from their parents.

But itís actually much more complicated than just random assortment. During the process of meiosis, chromosome 2 will align next to chromosome 2 and chromosome 4 will align next to chromosome 4 and so on and so forth. And this process is absolutely essential to ensure that each haploid sperm or egg inherits exactly one copy of all the different chromosomes.

More than just being essential for the inheritance of every single chromosome, it also allows a very special process to occur whereby chromosomes that are similar but not identical that line up can now exchange pieces of DNA. And this results in making completely unique chromosomes.

So now you've swapped a bit of chromosome 2 that your father inherited from his mum with a bit of chromosome 2 that he inherited from his dad. And the end result is a chromosome 2 that is neither your dadís, nor is it your grandmaís nor is it your grandfatherís. Itís completely unique. Itís got a bit of both grandmaís and granddadís and that is the chromosome that your sperm that made you inherited. Itís completely unique to that sperm.

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Cameron Lapworth asked the Naked Scientists: Hi Chris, Firstly Love the show. I was wondering what mechanism causes children born to the same parents all have different characteristics from each other? I understand that half the Chromosomes come from the father and half the Mother so you'll always get a mixture of both parents characteristics. However, this simple understanding doesn't explain why they aren't all identical twins (albeit born at different times). So are the Chromosomes somehow jumbled further say chromosomes no. 2 from Mum and no. 4 from Dad? What mechanism controls individuality? Ta, Cameron Lapworth What do you think? Cameron Lapworth, Thu, 22nd Jan 2009

There's more to human development than genetics but even if you just look at the genes there's a whole lot of possibilities.
For example, My dad's tall and fair haired and my mother's short with dark hair.
In very simplistic terms I could therfore be: short and dark; short and fair; tall and dark or tall and fair.
With millions of possible traits the number of possible combinations is huge Bored chemist, Thu, 22nd Jan 2009

Genes can also lay dormant and that is why a white couple can unexpectidle have a black child. Both parent would have had a black person in there genetic make up from past generations. I think they have made a film about it recently called SKIN. Make it Lady, Thu, 22nd Jan 2009

The chromosomes of a cell undergoing meiosis separate in different ways. If crossing over is ignored, a cell with two chromosomes can produce four different kinds of gametes; and with each additional pair of chromosomes, the number of possibilities double.

Chemistry4me, Thu, 22nd Jan 2009

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