Micro Life Zone
Asked by lara to Anissa, Eleanor, Mia, Sam on 4 Sep 2013.
Keywords: chromosomes, species
Lara, I like your question 😀
Here is my go at: Chromosomes vary in number and shape among living things. Most bacteria have one or two circular chromosomes. Bacteria are far simpler organisms! Humans, along with other animals and plants, have linear chromosomes that are arranged in pairs within the nucleus of the cell. Turns out the only human cells that do not contain pairs of chromosomes are reproductive cells, which carry just one copy of each chromosome. When two reproductive cells unite (the egg and the sperm), they become a single cell that contains two copies of each chromosome.
The difference in chromosome number between species is linked to different species gaining and loosing whole chromosomes through genetic accidents, like non-disjunctions, or breaks. This happens during cell division and chromosome formation.
Hey lara, thanks for your question! This all comes down to evolution and changes in your DNA! As you grow and develop, and your DNA is passed on to your offspring, it doesn’t always go to plan. Just like you make mistakes in school with reading and writing, your enzymes can make mistakes copying your DNA and dividing your cells! When this happens, you can end up with bits of your chromosome (which is a massive package of DNA wound up really tightly) can be chopped off! Bits can be added from somewhere else by accident, extra copies could accidentally be made, or or big chunks can be swapped and mismatched!
Normally when this happens, it would kill an embryo before or shortly after it is born. But sometimes, they survive! If they can survive and reproduce, then their extra or less DNA/chromosomes will be passed on too. Remembering that this obviously doesn’t happen over a short time, it happens over millions to billions of years, only a few times successfully in that amount of time!
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My pleasure lara!
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