DNA AND GENETICS DNA is the basic carrier of genetic information in almost all forms of life and in all cellular life. In humans and higher order animals, each cell (except red blood cells) will have the complete DNA message, even though not all genes are expressed in every cell. There is nuclear DNA and mitochondrial DNA. Because no mitochondria enter the ovum from the sperm cell at the time of conception, all mitochondrial DNA comes from the mother. As mentioned, there are four bases in DNA. These include adenine (A), thymine (T), cytosine (C), and guanine (G). The order of the bases in the DNA molecule is known as the “DNA sequence”. The double helix of the DNA consists of two sequences that match with each other. The base pairs are connected by means of weak hydrogen bonds, with certain bases only matches of A with T and G with C. This means that the complementary base is found on the opposite DNA strand. Figure 30 shows what the DNA strand looks like:
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