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Cell Reproduction

6-1 Chromosomes

Home | 6-1 Chromosomes | 6-2 Mitosis and Cell Division | The Cell Cycle | 6-3 How Gametes Form: Meiosis | Vocabulary

A chromosome is a library of genetic information. Each chromosome consits of one long strand of DNA wrapped around chunks of protein.

What are chromosomes?
The growth and development of your cells are carefully controlled by a set of instructions found inside the cell nucleus. The set of instructions, which is encoded in long molecules of DNA, is what determines that you are a human and not somethign like a fruit or an animal. The molecules of DNA look like spaghetti on a plate, but they are more then a intertwined mass. The long molecules are wound around pieces of protein. Which leads to chromosomes, which are compacted, creating bodies of DNA and protein.


We have learned more and more about chromosomes since we have discovered them. Eukaryotic chromosomes are made of chromatin. Which is a complex of DNA and protein. The DNA of a chromosome is a very long double-stranded thread that forms into a compact rod-shaped body. Our chromosome contains just about half a billion (500,000,000) nucleotides in its thread of DNA. Because they are way to long to fit into a cell, it is compacted into a smaller more managable structure.

How many chromosomes do you think you have? 15, 27, 50 or as many as 100? Unfortunately none of those are the right amount. We have 46 chromosomes, 23 pairs. A set of chromosomes are called a karyotype. In each pair, the two of them are similar in look. The are practically identical twins. They are like that because that have the same genes, in the same order. When you have 23 pairs of chromosomes, that is said to be diploid. A good way to remember this is that, di, meaning two,and there are two things in a pair. Basically all of our cells are diploid, but there is one exception. The chromosomes in your gametes only have one copy of each chromosome. Which is called haploid. A way to remember that is haploid kind of sounds like halve-loid, and there are only half of the chromosomes we usually have.


Ever heard of Sex Chromosomes? No? Well, it played a big part in your life, becuase of these little guys, you are what you are. Sex chromosomes, which are the chromosomes that determine whether you are male or female. Sex chromosomes are one of the 23 pairs and have special names. X and Y. Boys have one X and a little Y, girls have two X's. Because we are girls and only have X's, that means we can only produce eggs that contain an X chromosome. Guys have and X and a Y, so therefore their sperm can have a X or a Y. So ultimately our dads 'picked' our gender.

"Biology is the only science in which multiplication means the same thing as division."