DNA is the substance that makes us each different individuals. Nobody has the same DNA. This is what makes us unique. It used to be that we had no idea of what DNA looked liked. That all changed when James Watson and Francis Crick came along. These two scientists suspected that DNA was in the shape of a helix. They used old copper wire to make models for their idea. It turns out that they were correct in their assumption. DNA is in the form of a double helix.
These two different kinds of fish both contain different amounts of guanine and adenine in their DNA
One of the most important discoveries about DNA was discovered by Erwin Chargaff. He made two very important rules. His first rule is that in all kinds of DNA there will ALWAYS be the same amount of thymine and adenine. So if there was 30% thymine, then there was 30% adenine. This is the same thing for cytosine and guanine. His second rule involves the amount of adenine and guanine. The rule states that in different species there is different proportions of adenine and guanine. This means that a dog may have 20% adenine and 10% guanine but a bird will have 10% adenine and 20% guanine.
The base pairs of DNA are able to bond via hydrogen bonds. These hydrogen bonds are inbetween the two bases and they hold the two strands of DNA together. Since there are only two kinds of pairings it further proves Chargaffs first rule.
A chromosome is the structure that actually contains the DNA. A chromosome consists of DMA and all of the proteins that are associated with DNA. This structure is responsible for carry most of a cells genetics. Each different kind of species will have a different chromosome number. This is the amount of chromosomes in an animals cells. Typical female human chromosomes will tend to have two X chromosomes (XX). A typical male human will tend to have one X and one Y chromosome. When a cell is about to divide it will copy its chromosomes. A chromosome will consist the of one molecule of DNA.
A karyotype is the amount of chromosomes in a cell nucleus and it is also the appearance of those chromosomes. A karyotype is really an image that will show the reader how many chromosomes there are and what they look like.