Section 5 : DNA and Traits - Part D

Heredity: passing traits from one generation to the next.

click to find the answer to today's question What color are a person's eyes if they have no gene for pigment color?

Human Karyotype

 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

The Human Genome Project link to an Internet Website

In 1990, the U.S. Department of Energylink to an Internet Website and the National Institutes of Healthlink to an Internet Website 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.

Project goalslink to an Internet Website are to discover all the approximately 100,000 human genes and make them accessible for further biological study.

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:

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:
  1. The dictionary is not in alphabetical order.
  2. All the letters in the dictionary are in the correct order, but there are no breaks between the words.
While this dictionary is much better than nothing, there is still a lot of work to be done before we can easily use it.

Genetic engineering: the application of molecular genetics for practical purposes.

mapping genes on chromosomes

Genetic disorders:

The 23 pairs of human chromosomes contain over 40,000 genes. This complexity provides for many possible variations. The chromosome locationlink to an Internet Website 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 testinglink to an Internet Website is used to identify some problems. However, population sampling and pedigree studies are still used to track many genetic problems.

Assignment 1.5d  - DNA and Traits
Scoring criterialink to a local webpage

Part 1

  1. Use this site link to an Internet Website 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).
    1. What is the location of the code (be specific)? How many bases are we examining?
    2. What is the importance of on/off switches or gene promoters?
    3. Why is the codon ATG important? What is its function?
    4. How many stop codons do we know of? What is there function?
    5. Discuss the difference between  introns & exons in DNA.
    6. What is hitchhiking code? How do you think it ended up in our DNA?
    7. How does ancient code connect us with other organisms?
    8. Explain what you think "sites of variation" in our DNA cause to happen in our characteristics?
    9. How long is a gene (number of bases)?
    10. Which parts of the chromosome actually make up the gene (the parts that are actually coded or read)?
    11. What is the product of a coded gene?

Part 2

  1. In your own words describe/give an example of the following:
    1. polygenic traits
    2. recombinant DNA
    3. gene testing - What is it? How is it done?


  2. Chromosome #9 has a gene known to be responsible for what type of cancer?
  3. Two genes, located on different chromosomes are known to be associated with Alzheimer's Disease. What two chromosomes are involved?
  4. On which of the 23 pairs of human chromosomes is the gene associated with the Fragile X syndrome found?
  5. What does Fragile X syndrome cause?

Part 3

  1. How is a Karyotype performed? What is it used for?
  2. Go to the following site and complete the Karyotypinglink to an internet website exercise:
    1. Print off the following handout for the Karyotyping activity. link to a local webpage word to local webpage
    2. Read through all directions carefully: Evaluate three patients chromosomes, notate and diagnose.
    3. Research different genetic disorders and write a summary for each.
    4. Attach this with the previous questions.

Research Links:

                            Genetics Page










                            If a person has no gene for pigment color, their eye color will be red because of the blood in the eyes.