Download blue student worksheet - Warren County Schools

Blue People of Kentucky
Genetic Research Activity
Name ____________________________________
Period ___________________________________
Background:
In normal blood hemoglobin is an abundant protein that carries oxygen. Some of the
hemoglobin is in an altered form called methemoglobin. Methemoglobin is converted to
hemoglobin by an enzyme called cytochrome b5 reductase. In people with
methemoglobinemia the enzyme is not functioning properly and they have too much
methemoglobin in their blood which gives their skin a bluish color.
There are several causes of methemoglobinemia. The most common is acquired by
exposure to chemicals like benzene or certain antibiotics. Even infants that eat too many
beets can turn a blue color. It disappears when the chemicals are gone. The Fugates had
an inherited form of the disease. Oddly enough, the treatment for the disease was a blue
dye called methylene blue. When given a small dose the patients’ skin became normal.
Genetics:
http://www.nclark.net/Pedigree.gif
Look at the Pedigree and
Answer the related
questions:
1. Martin Fugate had 7
children, 4 with blue
skin. Some records
indicate that Martin had
blue skin. According to
the pedigree was his
skin blue or normal?
2. What is a possible
explanation for why Benjy Stacy was blue at birth even though he
is heterozygous for the trait?
3. Why weren’t any of John and Luna’s 13 children blue?
The Central Dogma of Biology:
DNA  mRNA  Protein
4. What was the name of the enzyme that changed methemoglobin into hemoglobin?
In the Fugate family the genetic disorder was methemoglobinemia type I, a form of the
condition that has no apparent effects other than blue skin. Go to the web site:
http://omim.org
This website, Online Mendelian Inheritance in Man, is a database of human genes and
genetic disorders. Look up the disorder by using either the name of the enzyme or the
name of the disorder and answer the remaining questions. You may have to read some
descriptions and make a decision about which link to choose.
5. What is the location of the gene that codes for this enzyme?
6. On which chromosome is it found?
7. The gene of interest is a section of DNA that codes for the enzyme cytochrome b5
reductase. Enzymes are proteins that are made of chains of amino acids.
Methemoglobinemia type I is the result of a substitution mutation that results in one
amino acid being changed to another. In OMIM search using:
CYTOCHROME b5 REDUCTASE 3
Read through some of the material and find a possible amino acid switch and identify
the amino acids involved. Use the amino acid abbreviation chart provided. There are
several possibilities; be sure to correctly match the mutant amino acid to the original
normal amino acid. These variants show that a different mutation can affect the same
gene and may change how that gene is expressed.
a. Normal Amino Acid ____________________________
b. Mutant amino acid _____________________________
Amino Acid abbreviation chart:
A similar chart can be found here: http://mendel.ethz.ch:8080/Server/ServerBooklet/_17545_tabular870.gif