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When studying genetics, you may come across some unfamiliar words or terms. It is important that you understand certain words and terms related to genetics to correctly apply what you know about your rabbits. Following are some common genetic-related words and terms and their definitions. I have tried to put them into everyday language so you can understand what they are and how they relate. To give you an understanding of how these genetic words and terms work I’ll be using examples with the A locus (or gene set) of the rabbit. This is also known as the Agouti pattern locus. Three genes or alleles make up this locus, "A (agouti)", "at (tan)", and "a (self)". I recommend that you come back once you have made it through the unit on the A locus and re-read this section, to see if it makes more sense afterward.
LOCUS & ALLELE
Locus (plural loci): “Locus” is the location of certain genes on a chromosome. To simplify, the locus is the set of genes that make up a particular characteristic. For rabbit colors, there are five major loci: A, B, C, D, and E. The A locus refers to the agouti hair pattern. I will delve more into these letters as we go along.
Allele: Each locus is made up of several possible genes. Each of these combinations is known as an allele. For the A locus, there are three possible genes: A, at and a. They will always be present in any combination of two genes. The sire will pass on one gene from each of his alleles to his offspring, and the dam will pass on one gene from each of her alleles to her offspring- each parent contributes one of the offspring’s pair of genes.
Allele: Each locus is made up of several possible genes. Each of these combinations is known as an allele. For the A locus, there are three possible genes: A, at and a. They will always be present in any combination of two genes. The sire will pass on one gene from each of his alleles to his offspring, and the dam will pass on one gene from each of her alleles to her offspring- each parent contributes one of the offspring’s pair of genes.
HETEROZYGOUS & HOMOZYGOUS
Hetero means “different” and homo means “same.”
Heterozygous: The two genes in the allele are NOT the same. I.e., Aa, Aat, ata.
Homozygous: The two genes in the allele are identical. I.e., AA, atat, aa.
Heterozygous: The two genes in the allele are NOT the same. I.e., Aa, Aat, ata.
Homozygous: The two genes in the allele are identical. I.e., AA, atat, aa.
DOMINANT & RECESSIVE
Dominant (Expressed): The stronger of the two genes. This is the gene you will see in the rabbit, it is visible.
Recessive (Carried): The weaker of the two genes, the “backup” gene. This is the gene that is carried but not seen. It is hidden.
A great example that I use to explain recessives and dominants using the A Locus of Agouti, Tan, and Self patterns (note the A locus is the Agouti locus, which is a fur pattern): picture these three patterns as people. The front person is large and round, representing agouti- A. Next, we have the middle center person who has a medium build, representing tan- at. Last, we have a skinny person representing self- a. If the large person (agouti- A) is standing in front of us, we wouldn’t know who was hiding behind him. It could be a medium person (tan- at) or a skinny person (self- a), or he could even have another large person of the same size (agouti- A). We don’t know which; we just know that because this person is large (aka dominant), he can easily hide someone of equal size or smaller behind him. Next, we have the medium guy (tan- at). He can’t hide a large person (agouti- A) behind him- we’d see a large person trying to hide behind him. But he could hide another medium person (tan- at) or a skinny person (self- a), right? That means your tan- at rabbit can either have another tan- at or a self- a gene hidden. Finally, we have the skinny guy, self- a. No one can hide behind him except another skinny person, self- a. The rule is, the smaller the guy, the less he can hide behind him. The bigger the guy, the more he can hide. In other words, the more dominant a gene, the more genes can hide behind it. The more recessive a gene, the fewer genes that can hide behind it.
In most cases the dominant genes and recessive genes don’t act like mixing two cans of different colored paint. A completely dominant gene will override and hide the recessive gene. You will only see the dominant color. One exception to this is in the C locus, which has incomplete dominant genes. More on that when we reach the C locus unit.
Recessive (Carried): The weaker of the two genes, the “backup” gene. This is the gene that is carried but not seen. It is hidden.
A great example that I use to explain recessives and dominants using the A Locus of Agouti, Tan, and Self patterns (note the A locus is the Agouti locus, which is a fur pattern): picture these three patterns as people. The front person is large and round, representing agouti- A. Next, we have the middle center person who has a medium build, representing tan- at. Last, we have a skinny person representing self- a. If the large person (agouti- A) is standing in front of us, we wouldn’t know who was hiding behind him. It could be a medium person (tan- at) or a skinny person (self- a), or he could even have another large person of the same size (agouti- A). We don’t know which; we just know that because this person is large (aka dominant), he can easily hide someone of equal size or smaller behind him. Next, we have the medium guy (tan- at). He can’t hide a large person (agouti- A) behind him- we’d see a large person trying to hide behind him. But he could hide another medium person (tan- at) or a skinny person (self- a), right? That means your tan- at rabbit can either have another tan- at or a self- a gene hidden. Finally, we have the skinny guy, self- a. No one can hide behind him except another skinny person, self- a. The rule is, the smaller the guy, the less he can hide behind him. The bigger the guy, the more he can hide. In other words, the more dominant a gene, the more genes can hide behind it. The more recessive a gene, the fewer genes that can hide behind it.
In most cases the dominant genes and recessive genes don’t act like mixing two cans of different colored paint. A completely dominant gene will override and hide the recessive gene. You will only see the dominant color. One exception to this is in the C locus, which has incomplete dominant genes. More on that when we reach the C locus unit.
GENOTYPE & PHENOTYPE
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Genotype: What the genes are- the list of the rabbit’s loci and alleles. Genotype is typically displayed in a series of letters that represents the genes that create the color and pattern of a rabbit. These letters tell us what the rabbit will look like. For example, a chestnut (wild color) rabbit’s genotype might be Aa Bb CC Dd Ee. More on what each of these letters means as we go along.
Phenotype: What you SEE visually on the rabbit. The chestnut rabbit above has a simpler PHENOTYPE than GENOTYPE. The genotype is Aa Bb CC Dd Ee, but the phenotype is chestnut.
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MELANIN: EUMELANIN & PHEOMELANIN
Melanin: Melanin is a pigment found in most organisms that is produced by cells known as melanocytes. These cells are present in the skin of most animals, including rabbits. Melanin affects everything from skin color, hair color, and eye color. Melanin comes in two basic forms and can range from yellowish-red to dark brown.
Eumelanin: Eumelanin is the most common form of melanin and is brownish in color.
Pheomelanin: Pheomelanin is the other basic form and produces a reddish-brown color that is often associated in humans with freckles and red hair.
Eumelanin: Eumelanin is the most common form of melanin and is brownish in color.
Pheomelanin: Pheomelanin is the other basic form and produces a reddish-brown color that is often associated in humans with freckles and red hair.
PUNNETT SQUARESPunnett Squares are SUPER useful tools! They are a square diagram that is composed of a grid of usually four boxes and is used to calculate and depict all the combinations and frequencies of the different genotypes and phenotypes among the offspring of a cross. Note: Each result represents the possibility for each kit, not for the whole litter.
We will dive further into Punnett Squares later in the lessons. |
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