DNA Day experts answer your questions about extra chromosomes

Above: Image © Susan Chiang, iStockphoto.com

How do extra chromosomes form?

Often times extra chromosomes are inherited (not formed), when a child gets an extra chromosome from either the mother or the father. This may be because during the process of meiosis, the chromosome did not separate properly leading to either one less or one more chromosome in the gametes (egg or sperm). If this gamete is fused with the gamete of the other parent, it leads to either an extra or one less chromosome in the child there there actually should be. This improper separation of chromosomes is called Non-disjunction.

- Answer provided by Harman Sawhney

Why does having an extra chromosome like with Down Syndrome have so many consequences?

Hi there! Here's an important concept to remember: too much or too little is bad. Too much water and you would die of water poisoning and too little of dehydration. The same holds for many biological systems, especially when it comes to chromosome counts in mammals. An extra chromosome means an extra copy of a set of genes which means more of whatever the genes are encoding, which the body may not be able to cope with. Furthermore, when you have this extra number when it comes to mitosis the pairing of the chromosomes would be strange, because you have an extra copy!

- Answer provided by Ethan Yang

How does a tetraploidy system work in fungi and why do they differ from other organisms?

I'm not a "yeast guy", but the tetraploid system allows an unusual life cycle in yeast. My understanding is that the benefit is thought to be through allowing the exchange of genetic material and the cycling through of different life stages that may be better adapted to different environments.

- Answer provided by Dr. Thomas Merritt

What is partial trisomy?

It means that instead of one extra copy of an entire chromosome, only a part of that chromosome has been duplicated and is present above the normal number.

- Answer provided by Dr. Aaron Goodarzi

Where does the XXX syndrome effect in the body?

It occurs in girls only, roughly 1/1000 and happily quite often, even though this is a chromosome abnormality, there are few symptoms. Those that exist are quite varied, and seem to relate to how may cells are actually XXX and how many are the normal XX.

- Answer provided by Jay Ingram

Can a person have 2 sets of DNA? How does that work and what problems could be associated with it?

We all have two sets of chromosomes which are separated during meiosis and each set from father and mother is passed on to the next generation. Any variations on meiosis we would likely never find out about because they would be lethal to any offspring and therefore the offspring would never arise.

- Answer provided by Dr. Gijs Van Rooijen


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