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DNA Sequencing and the Human Genome

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  • 0:01 Importance of DNA Sequencing
  • 0:54 Structure of DNA
  • 1:17 Human Genome Project
  • 2:17 How Is DNA Sequenced?
  • 3:58 Applications of DNA Sequencing
  • 5:18 Lesson Summary
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Lesson Transcript
Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

DNA sequencing allows us to determine the exact genes that make up an individual. It can be used to screen for certain diseases and in crime scene analysis. Learn more about it in this lesson.

The Importance of DNA Sequencing

You probably already know that your DNA determines everything that happens in your body and that changes in DNA can lead to many different diseases and disorders. Have you ever wondered how exactly we know what genes are encoded in DNA and how they vary from person to person? Humans have 23 chromosomes that each contain many genes. The complete set of all the genes on all the chromosomes is known as the human genome.

Although there are many genes that are exactly the same in all people, there are also differences that make each person unique. You have a genome that is different from everyone else's! It determines your hair color, how tall you are, and what diseases you are more likely to develop, among many other things.

In this lesson, you'll learn about the methods that are used to sequence DNA. You will also learn about how the entire human genome was sequenced and about how DNA sequencing is used today.

Structure of DNA

DNA is made of only four nucleotide bases, thymine (T), adenine (A), guanine (G), and cytosine (C). Each gene is simply a specific sequence of these four bases. In a chromosome, two long strands of DNA bind to each other and form a coil that looks like a double helix. There are 23 distinct chromosomes in each of your cells, each one containing many genes. DNA sequencing is the method of determining the exact sequence of nucleotide bases in a chromosome.

Human Genome Project

Although we have known about the structure of DNA for a long time, it wasn't until relatively recently that we were able to sequence the entire human genome and know all the genes that are contained in a human like you! In 1990, a massive international research project called the Human Genome Project to sequence the entire human genome was proposed and funded by the United States government. Scientists all over the world worked on this for over ten years, and finally, in 2003, it was declared to be completed.

Several donors, both male and female, donated blood and other tissues over the years to this project so the genome could be determined. Of course, each person has genes that are unique, so even though we now know the locations of all the genes in a human genome, those genes may differ from person to person. Mapping those differences is something that scientists are working on now.

How Is DNA Sequenced?

How exactly did scientists first sequence the human genome? The first method used to sequence DNA was developed by Fred Sanger in the late 1970s, and this basic method was used to complete the Human Genome Project in the 1990s and is still used today. The Sanger method is a method of DNA sequencing that incorporates chain terminating nucleotide bases that will stop the copying of DNA when it gets to a particular base.

To sequence DNA using Sanger's method, you must first separate the two-paired DNA strands. Then, you make copies of each piece of DNA but include special nucleotide bases so that the copy will stop when it gets to a certain base (either A, T, C, or G). By doing this over and over for all the bases, you can identify exactly where in the genome each base pair is located. To get the entire sequence, you then have to fit all these little copies together, like a jigsaw puzzle.

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