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How do Siamese Cats get their color? - Abdullah Naeem
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How do Siamese cats get their coloring and how does this relate to how humans get their traits?
By:
Abdullah Naeem
What is a Siamese Cat?
A Siamese cat is a type of Asian cat that is known for its very distinct fur color pattern that's shown below.
1
My Initial Model
The Siamese cat is colored in this distinct way due to a flaw or a change in its DNA.
In order to verify this however, first we must compare the DNA of the Siamese Cat to that of a domestic cat.
1A
What is DNA?
-DNA is a deoxyribonucleic acid that is made in a double helix form.
-DNA also is a code for all of your traits and can be found in every living thing.
-DNA exists in every cell inside the nucleus.
1A (cont.)
DNA Composition
DNA is a nucleic acid and this means that it is made up of nucleotides.
A nucleotide is made up of a deoxyribose sugar that is paired to a nitrogenous base and a phosphate group.
The 4 different types of nitrogenous bases are Adenine, Thymine, Cytosine, and Guanine.
According to Chargaff's rule, the % of Adenine is equal to the % of Thymine. The % of Cytosine is equal to the % of Guanine.
Adenine always pairs with Thymine and Cytosine always pairs with Guanine in DNA
Thymine and Cytosine are pyrmiridines (single ring) while Adenine and Guanine are purines (double ring structure)
cont.
DNA EXTRACTION
1A (cont.)
In order to study the DNA, we first had to extract the samples.
-The steps for this was to first break open the cell membrane and the nuclear membrane.
-Then you had to denature the histones to separate it from the DNA.
-Then you had the final DNA sample that could be extracted.
After extracting the DNA, you still have to use gel electrophoresis, use DNA sequencing, and Gene comparison
Steps after extracting
DNA
The first step after you have extracted a DNA sample is to put it through a Gel Electrophoresis machine to find the gene of interest
This machine starts with DNA samples being loading into the "wells" at the top of the machine and this DNA then slowly begins to separate down.
This is because the machine runs an electric charge through the DNA which separates the sample based on the size and weight.
After Gel Electrophoresis, you make multiple copies of the gene of interest (polymerase chain reaction) and then cut them up using restriction enzymes
Cont.
Steps after Gel Electrophoresis
DNA SEQUENCING
After Gel Electrophoresis, you have to use different methods of DNA Sequencing.
-The first method is called the Sanger Method and that's where you determine the nitrogenous base pairs (A, T, C, G).
The second method is called Shotgun Sequencing and thats when you see where the fragments from Sanger overlap to determine the order of the bases.
Steps after DNA
Sequencing
After you separate and sequence the DNA, you can You compare the order of bases between DNA samples to see similarities and differences.
Below is the first 20 "triplets" of the sequence from the genes of a domestic and Siamese Cat.
DNA Comparison
Domestic Cat:
tac - atg - gtg - cat - ctg - acg - cct - gag - gag - aag
tct - gcc - gtt - act - gcc - ctg - tgg - ggc - aag - gtg
Siamese Cat:
tac - atg - gtg - cat - ctg - acg - cct - gag - ggg - aag
tct - gcc - gtt - act - gcc - ctg - tgg - ggc - aag - gtg
Gene Comparison
between the cats
The difference between both of the cats is a change in the 9th triplet between the Adenine base and the Guanine base
But, what is this change called?
Changes to DNA
Changes to DNA strands are called mutations.
A mutation can be passed down to offspring through sex cells.
A mutagen is a chemical or physical agent in the environment that can cause a mutation.
2
Different types of
Mutations
The three different types of mutations are substitution mutations, insertion mutations, and deletion mutations.
Mutations
Substitution Mutation
Substitution mutations is a mutation where a nitrogenous base pair is substituted out with another nitrogenous base pair.
The reason this can change traits of an organism is that the mutated base pair can lead to a different protein being made which can alter certain traits.
Substitution
Insertion Mutation
Insertion Mutation is when there is a nitrogenous base pair added to a DNA sequence. This change is a big change since it disrupts the order of every triplet that comes after the mutation. Insertion Mutations are also referred to as a frameshift mutation since it changes the entire frame of the DNA sequence.
Insertion
Deletion Mutations
A deletion mutation is when a nitrogenou base pair is taken out of the DNA sequence. This is another example of a frame shift mutation since it changes all the triples that occur after the mutation.
Deletion
How mutations impact
traits
How mutations impact
traits
- Mutations affect traits by first affecting DNA. When the DNA is changed, it affects the corresponding RNA. Before you can make proteins, you have to transcribe the DNA into RNA.
-When transcribing, you should know that there is no Thymine in RNA, it is now Uracil so Cytosine pairs with Guanine and Adenine now pairs with Uracil when you are transcribing DNA into RNA.
cont.
The DNA triplets are turned into RNA codons through transcription.
This RNA eventually is translated into amino acids (proteins) through messenger RNA.
Each codon codes for a certain protein and this protein codes for your traits. This is how a mutation in your DNA can affect the RNA which affects the protein made which ultimately affects your traits.
cont.
RNA to protein chart
Part of recipe making
Where this occurs in cell
Cell structure that it represents
cookbook DNA(makes recipes) Nucleus
scribe DNA polymerase Nucleus
turns DNA into RNA
Recipes RNA nucleus +
cytoplasm
Example
Chefs Ribosomes Cytoplasm
Meals Proteins (amino acids) Cytoplasm to
where needed
Denaturation
Denaturation is a process in which proteins/enzymes lose their structure and they "unfold" their fibers which alter their function.
Things can be denatured by either being exposed to a different temperature (too hot) or by being in an environment with an altered pH level.
3
Altered Model
In the middle of the investigation, I thought that the color of the Siamese cats might have been the way it was due to something wrong with its pigment cells. After further investigation I found the following
How do Siamese Cats get
their color?
Color of the Siamese Cats
Investigation
When an organism has no color and is white, it is called albinism. Organisms that do have color get the color from molecules called pigments.
The main pigment found in organisms is called Melanin. Enzymes allow for the production of Melanin by turning the amino acid Tyrosine into other products which become Melanin.
This enzyme is called tyrosinase and it oxidizes tyrosine to turn it into Dopaquinone which then mixes with other things to turn into Melanin.
Organisms that are albino are normally albino since they have a mutation to their tyrosinase gene which results in a non functional tyrosinase which halts the production of melanin.
cont.
Final Model
Based on the last discovery about the enzyme tyrosinase, I have concluded that the Siamese Cat has a mutated tyrosinase gene. As I previously stated, the Siamese cat had a substitution mutation in the 9th triplet of its DNA sequence. This mutation caused a change in the enzyme tyrosinase and caused the enzyme to be more heat-sensitive.
4
Final Model cont.
Since the tyrosinase enzyme was more heat sensitive, it would denature easier and faster in regular temperatures.
-The reason that the Siamese cat is colored differently is because the body temperature near the center of the cat is around 101°F which is too hot for the tyrosinase enzyme to function.
It denatures due to this (heat) and the process for making melanin is halted which leaves those parts of the cat white.
Final Model cont.
The places which are farther away from the center of the cat, the extremities (ears, paws, tail), are colored since the temperature of those places is around 77°F which is ideal for the mutated tyrosinase to work.
This shows that the Siamese cat only gets colored in cold extremities and cold environments and also shows that the reason for its color is due to a mutated tyrosinase enzyme.
How does this relate to how humans get their traits?
Part 2
This relates to how humans get their traits since humans also experience mutations in the DNA which lead to altered proteins as well.
A tiny mutation in a DNA sequence can have a domino affect that can change the very traits of an organism.
Humans get their traits through proteins and the Siamese cat does as well.