I am glad that you are enthusiastic about learning genetics! :) At times you may have trouble understanding what I am talking about and that is normal. But PLEASE tell me when you are having trouble because it will only get more confusing if you keep going without asking questions. 
With that in mind though, this is going to be fun. :)
Okay, so here is my guide about genetics. If you are ever stuck you can refer to this to see if that helps.
https://docs.google.com/file/d…WxReEIyLU56V0E/edit?pli=1
So first things first. Skin color is controlled by pigments called Melanin. Everything has it. Melanin protects your skin from the sun.
"Melanin: The pigment that gives human skin, hair, and eyes their color. Dark-skinned people have more melanin in their skin than light-skinned people have. Melanin is produced by cells called melanocytes."
There are two different types of melanin cells in cats. Eumelanin and Pheomelanin. Eumelanin is the normal type and Pheomelanin is the mutated type.
Eumelanin is what makes a cat look black, chocolate, or cinnamon. When the cat has the mutated version called Pheomelanin, the cat loses the ability to produce melanin and the cat ends up looking red/orange.
So we are first going to focus on Eumelanin colors because those are the easiest to start with.
Okay, we will go over some basics. I will put key words in bold and I will provide a short key words list at the bottom of each lesson.
A Gene is a trait that is passed from parent to offspring. Number of toes and hair color are examples of different types of different genes.
In this case we will be talking about cats and for each gene, a cat will get two alleles (one from the mother and one from the father).
In this case, we have 3 different alleles that code for normal coat color. This gene is often referred to as the cat's Base Color. So if you see anyone talking about the Base Color of a cat, they are referring to the Eumelanin colors.
In cats, the Black Phenotype is the most dominant and will show up as the cat's color as long as they have at least one "B" allele. The Chocolate Phenotype is the second most dominant and will only show up if the cat doesn't have a "B" allele but DOES have at least one "b" allele. The Cinnamon Phenotype is recessive to both Black and Chocolate and will ONLY show up if the cat receives a "bl" from both parents.
Black = BB, Bb, or Bbl
Chocolate = bb or bbl
Cinnamon = blbl
So from looking at which alleles code for black, chocolate, and cinnamon, you should be able to see which allele is the most dominant and which allele is the most recessive.
Now when a cat has two of the same allele (ex: BB) the cat is said to be homozygous for that trait. And when a cat has two different alleles (ex: Bb) the cat is said to be heterozygous for that trait.
Each set of traits has two different ways of describing it. The phenotype and the genotype.
Phenotype refers to the the physical description of that allele.
Genotype refers to the genetic description of that allele.
For Base Color, the phenotype refers to the colors (black, chocolate, and cinnammon), and the genotype refers to the allele combination (ex: BB, bb, blbl).
To figure out what color the kittens will be when you cross two Eumelanin colored cats, you set up a punnet square using the genotypes of the parents. :)
Click Here for a Punnet Square reference PDF
For now we are going to assume that these cats are homozygous for Base Color. Since the base color isn't gender specific, it doesn't matter which is the male and which is the female, but I will let you know which is which.
So if we were going to do a cross of a male Black cat and a female Black cat, the punnet square would look like this:
B B
B BB BB
B BB BB
What does this mean? This means that when crossing two black cats that are both Homozygous for that trait, the phenotype of all of their offspring will be Black.
So if I were to write this out it would look like this:
Black x Black
Black
So when you do pairings, you will write out your answers like this: (replacing the male, female, and offspring with colors of course) When you are doing pairings for other people you don't have to write out the punnet square, but for practice I want you to write it out.
Male x Female
Offspring
B B
B BB BB
B BB BB
Gene - A gene is a trait that is passed from parent to offspring (Ex: Base Color)
Allele - An allele is a varation of a gene (Ex: There are three different Base Colors that a cat can be, so there are three alleles that code for Base Color)
Genotype - The genetic code of a gene (Ex: BB, bb, and blbl)
Dominant - A dominant allele produces a dominant phenotype. Only one parent needs to pass of the gene in order for it to show.
Recessive - A recessive allele produces a recessive phenotype. Both parents need to pass on a copy of a recessive allele in order for it to show.
Phenotype - The physical description of a gene (Ex: Black, Chocolate, and Cinnamon)
Melanin - The pigment that gives skin, hair, and eyes their color. Dark-skinned individuals have more melanin in their skin than light-skinned individuals have.
Eumelanin - One of the basic and most common type of melanin. Eumelanin produces the Base Colors for cats (Black, Chocolate, and Cinnamon).
Base Color - In cats, this refers to the three Eumelanin colors (Black, Chocolate, & Cinnamon)
Review Questions:
1) What does it mean for a trait to be dominant? recessive?
2) For base color, write out the colors (not alleles) in order of most dominant to recessive.
3) Based on the Genotypes, can you name the Phenotypes of the following cats?
BB =
blbl =
bbl =
4) Figure out the offspring of these cat pairings: (for these problems, assume that the parents are homozygous for their colors)
Black male, Black female:
Chocolate male, Black female:
5) Figure out the offspring for these cat pairings: (for these problems, assume that the dominant colored parent is heterozygous for the color of the recessive colored parent)
Cinnamon male, Chocolate female:
Black male, Cinnamon female:
**Make sure you follow the template that I used in the example above.** (You can copy and paste this template (below) if that helps - just replace the female with the female's color, and the male with the male's color)
Also, if you are like me and you learn well from visual examples you can watch this video. :)
[youtube][/youtube]
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Example:
~~For Homozygous pairings (only applies to the dominant color)~~
Black male, cinnamon female:
Step 1: Figure out which one is the dominant color. (In this case, Black is the dominant color)
Step 2: Figure out if the question asks for the dominant color to be homozygous OR heterozygous. (In this case the dominant color will be homozygous - two copies of the same allele).
Step 3: Write out the alleles:
Black (Homozygous) = BB
Cinnamon = blbl
Step 4: Create the punnet square:
Black
B B
bl Bbl Bbl
Cinnamon
bl Bbl Bbl
Step 5: Analyze the punnet square. (This shows that all of the kittens will be black since Black (B) is the dominant phenotype and there are no (blbl) pairings).
Step 6: Write out the paring as "Male x Female"
Black x Cinnamon
Black
Now if we were doing a heterozgous pairing it would look like this:
~~For Heterozygous pairings (only applies to the dominant color)~~
Black male, cinnamon female:
Step 1: Figure out which one is the dominant color. (In this case, Black is the dominant color)
Step 2: Figure out if the question asks for the dominant color to be homozygous OR heterozygous. (In this case the dominant color will be heteryzygous - one copy of the dominant allele and one copy of the recessive allele).
Step 3: Write out the alleles:
Black (Homozygous) = Bbl
Cinnamon = blbl
Step 4: Create the punnet square:
Black
B bl
bl Bbl blbl
Cinnamon
bl Bbl blbl
Step 5: Analyze the punnet square. (This shows that there can be black kittens and cinnamon kittens since both genotypes show up in the punnet square).
Step 6: Write out the paring as "Male x Female"
