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What color are a person's eyes if they have no gene for pigment color? |
Although some human traits are controlled by a single gene, most human characteristics are controlled by several genes. Polygenic traits are controlled by two or more genes. Skin and eye color are both influenced by the additive effects of from three to six genes. Each of these genes results in the formation of a certain amount of a pigment called melanin. The more of the genes that are expressed, the darker the color produced.
In humans the following characteristics are the results of interactions among several genes.
Polygenetic birth defects in humans
In 1990, the U.S. Department of Energy
Project goals
A news conference was held in June of 2000 to announce the completion of over 99% of the human genome. Scientists stated that they have mapped the order in which most of the nitrogen bases
occurring in the DNA molecules making up each of the twenty three pairs of human chromosomes. The press release from this news conference predicted that cures for most genetic diseases and disorders will be found within a few years. While this project is a great step forward in our understanding of human genes, there is still a very long way to go before mastering the subject. To put the current phase of the human genome project in prospective, think of it in this way:
Genetic engineering: the application of molecular genetics for practical purposes.
Genetic engineering can be used to identify genes for specific traits or to transfer genes from one
organism to another organism. Genetic engineers use different bacterial enzymes called restriction enzymes to cut DNA molecules at specific sites on the molecule. This allows individual genes to be isolated. Once the gene is isolated, a cloning vector is used to clone the gene and transfer it from one organism to another. These vectors are found in many bacteria and consist of a ring of DNA that is in addition to its main chromosome. This ring of DNA is known as a plasmid.
Recombinant DNA is a combination of DNA from two or more sources. One of the best applications of recombinant DNA today is in the production of insulin.
Gene therapy
Genetic disorders:
The 23 pairs of human chromosomes contain over 40,000 genes. This complexity provides for many possible variations. The chromosome location
Part 1 Part 2 Part 3
Research Links:
Human Genome - National Human Genome Research Institute
The Human Genome Project
and the National Institutes of Health
formally began a multidisciplinary project to map and sequence the human genome.
While the project was originally planned for 15 years, rapid technological
advances accelerated the expected completion date and was completed in 2003.
are to discover all the approximately 100,000 human genes and make them accessible for further biological study.
The information contained in all the human chromosomes is like a complete, unabridged dictionary for human proteins. Each of the terms in the dictionary represent a protein gene. The letters in the words making up the definition of each term represent the DNA bases that make up the gene. At the present time, the human genome project has given us a dictionary with two major weaknesses:
While this dictionary is much better than nothing, there is still a lot of work to be done before we can easily use it.
What is a clone? Basically, clones are organisms which have identical genetic material. Today, the term "clone" is most often associated with genetic engineering. However, using this definition of clone, identical twins are clones. The new plant that grows from a plant cutting is a clone. When you look at it this way, clones have been around for a very long time. Scientists have been using "lower" animals for years in artificial cloning experiments, but it wasn't until 1996 that Dolly came into the world.
You will learn more about cloning in part e DNA & traits.
The gene for human insulin is placed into the plasmid of bacteria cells and those cells produce insulin. This process has helped lower the cost of insulin needed to treat diabetes.
treats a genetic disorder by introducing a gene into a cell or by correcting a defect in a cell's genome. Gene therapy has been in use since 1990. There are still obstacles today regarding how and where to insert genes safely into an organism's chromosomes. But gene therapy is being used to treat cystic fibrosis, hemophilia, AIDS, and several forms of cancer. As more is learned about the human genome, gene therapy may one day provide permanent cures for genetic disorders.
of many disease-causing genes are known. While our ability to
interpret the complex human genome is increasing, we are still far from mastering it. Today, gene testing is used to identify some problems. However, population sampling and pedigree studies are still used to track many genetic problems.
Population sampling:
Sampling is done by carefully selecting a small group of individuals to represent the whole population. Data from studying these individuals is applied to the whole population statistically.
Pedigree studies:
A pedigree study produces a chart that traces a "history" of the traits of several generations. These studies frequently identify the carrier of a gene that is not visible.
Assignment 1.5d - DNA and Traits
Scoring criteria
to explore a stretch of the code found in a chromosomes (which is made up of
DNA) and answer the following question in your own words (summarize).
exercise:
word doc.
