Download Coloration in Jaguars Have you ever seen a jaguar in a zoo? Most

Coloration in Jaguars
Have you ever seen a jaguar in a zoo? Most jaguars are orange with dark spots. There are also jaguars
that are completely black, though. What do you think caused the difference in coloration between these two
animals? If you said that it might be a difference in their genes, you are right. The gene responsible for the
coloration of jaguars is called the melanocortin-1 receptor, or MC1R for short. The protein made from this
gene helps regulate the amount of pigment melanin that is made in many organisms. Melanin is a brown or
black pigment. The more melanin that is present in skin, fun, or feathers, the darker these tissues appear.
In jaguars, the typical allele produces a moderate amount of melanin. These jaguars appear orange
with spots. A small change in the MC1R gene can allow higher amounts of melanin to be produced, which
results in a black jaguar. The high amount of melanin does not allow the spots to be seen. (The spots on
jaguars are caused by a different gene.) The following sequence shows some of the MC1R DNA sequence for
the typical coloring and for the black coloring. Note that this is just a short portion in the middle of the
gene’s sequence. The entire MC1R gene is made up of several thousand DNA nucleotides, begins with a start
codon, and ends with a stop codon:

Typical jaguar:
GTG CTG GAG ACG GCC GTC ATG CTG CTG CTG GAG GCG GGC ACC CTG GCC GGC

Black jaguar:
GTG CTG GAG ACG GCC GTC ATG CTG CTG CTG GCC GGC
It is interesting to note that the MC1R gene is involved in differences in coloration in other animals,
too. One change in the DNA sequence of this gene causes the difference between white snow geese and bluegray snow geese. Changes in MC1R also cause the difference between the white and black forms of the black
bear and light and dark forms of certain lizards. The gene is also responsible for light and dark rock pocket
mice. In humans, most people with red hair have one particular allele of the same gene.
Resistance to Insecticide in Mosquitoes
Malaria is a disease that is common in many tropical locations in the world, such as Africa, Asia, and
South America. Malaria is caused be a parasite that is transferred to humans when they are bitten by an
infected mosquito. It is a serious disease that can cause a flu-like illness with fevers, chills, vomiting, and
joint pain. Sometimes malaria can be serious enough to cause death.
In the 1950’s, an effort started across the globe to kill the mosquitoes that carried malaria. This was
done using insecticides such as DDT. In some places, such as the southeastern United States and in Europe,
the effort was successful in wiping out malaria by the late 1970’s. In other parts of the world, there was not
as much success. As it turned out, a mutation in the DNA of the mosquitoes had caused them to be resistant
to insecticides. The live mosquitoes were still able to carry the malaria parasite and continue to infect
people.
What effect did the change in DNA that led to the insecticide resistance have? Mosquitoes and other
organisms have an enzyme called acetylcholinesterase, or AChE, in the synapses between neurons. This
enzyme helps remove a neurotransmitter called acetylcholine from the synapse. Insecticides cause the AChE
to work improperly to remove acetylcholine. This results in acetylcholine building up and causing the
mosquitoes to become paralyzed and die. The mutation cause a change in the AChE, though, that made it
resistant to the effects of the insecticides. This means the AChE could continue carrying out its typical
functions in the cell and the mosquitoes were able to live.
The following sequences show a part of the DNA sequence in the typical AChE allele and the
insecticide-resistant AChE allele. Note that this is only a small portion of the DNA sequence. The whole AChE
gene is made up of several thousand DNA nucleotides, begins with a start codon, and end with a stop codon:

Typical AChE:
CGG CGG CAG TAC GAC ACC TAG AAG CCC CCA CCG AAG ATG AGG CCC TGA CGG

Insecticide-resistant AChE:
CGG CGG CAG TAC GAC ACC TAG AAG CCC CCA TCG AAG ATG AGG CCC TGA CGG
Geese Living at High Altitude
Mount Everest rises above the country of Nepal, its peak soaring at 8,848 m (29,028 ft).
Temperatures are so cold that flesh will freeze instantly if exposed. Almost all of the climbers who attempt
to reach the top require bottled oxygen as they climb. The amount of oxygen available at that altitude is only
about a third of the amount available at sea level. Despite the harsh conditions, bar-headed geese fly over
the top of Mount Everest as they migrate from their feeding grounds in India to their nesting grounds in
Nepal.
The key to this type of goose being able to fly at such high altitudes is a special type of hemoglobin. In
these geese, the hemoglobin in their red blood cells is able to bind oxygen very quickly compared to
hemoglobin found in most geese. When a bar-headed goose breathes in, the oxygen binds to the hemoglobin
in red blood cells, even at extreme elevations where the oxygen pressure is low. The oxygen then moves to
all parts of the body, carried by the red blood cells. This gives the important systems such as the gas
exchange system and the muscular system, the power to fly at such high altitudes.
What changes have occurred at the protein level that allows the hemoglobin to bind to the oxygen
more quickly? Scientists have found that one change in the protein has caused the hemoglobin proteins to
differ between bar-headed geese and geese that live at low altitude. The following protein sequence shows a
portion of the hemoglobin protein in bar-headed geese and in greylag geese, a type of goose that lives at
lower altitude. Note that this is only a small portion of the protein sequence. The whole hemoglobin gene is
made up of several thousand DNA nucleotides, begins with a start codon, and ends of with a stop codon. This
results in a large protein with many more amino acids than are shown:

Greylag goose hemoglobin:
valine valine alanine isoleucine histidine histidine proline serine alanine leucine threonine proline glutamate valine histidine alanine serine

Bar-headed goose hemoglobin:
valine valine alanine isoleucine histidine histidine proline serine alanine leucine threonine alanine glutamate valine histidine alanine serine
Some scientists wanted to confirm that this change in amino acid sequence was what caused the
change in the hemoglobin. To do this, they took human hemoglobin and made the same amino acid change
at the same place in the protein. They found that the modified human hemoglobin bound oxygen more
quickly as well.
Use the following information to create an illustration of the process of gene expression for your topic. Your
teacher will direct you on the materials you may use. Your illustration should include the following criteria:
1.
2.
3.
4.
5.
The type of mutation that occurs and the nucleotides changed.
The mRNA that is the product of transcription.
The amino acid sequence of the polypeptide that is the product of translation.
The tRNA anticodons used in the synthesis of the polypeptide.
A description of how the mutation affects the organism’s phenotype.
If you are studying jaguar coloration or insecticide resistance in mosquitoes, you have been provided the
DNA sequence and will be able to work through the steps in order. If you are studying geese at high altitude,
you have been give the protein sequence and will work backward to the DNA sequence