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Basic Genetics and Definitions

Learning about Gene Inheritance and Punnett Squares!

Quick Definition Reference:
Genotype vs Phenotype: Genotype is the hidden genetic code. Phenotype is what is physically expressed.

Gene and Gene Series: Genes occur in different series within the genotype of the rabbit. Each series is responsible for affecting a different trait.

Allele: Variant form of a gene. Each gene series always contains TWO alleles.

Dominant vs Recessive: When an allele is dominant over the second allele within its gene series, it will be expressed over the more recessive allele. 

Homozygous vs Heterozygous: When a pairing of alleles is identical, it is described as "homozygous". When the gene series contains two different alleles it is "heterozygous".

Basic Gene Inheritance

Here we will focus on the genotype (the genetic code, or full set of gene series) of a rabbit, and how that genotype is defined and created. The genotype of a rabbit determines the phenotype (the physical appearance) of the rabbit.

 

Each gene series contains two genes. Each gene contains different variations on that gene and what is expressed, and those are called alleles. A rabbit inherits one allele from each parent to complete each gene series.  Capital and lowercase letters are very important when referring to these alleles, as they represent the different variations of their genes and their orders of dominance.  A dominant allele typically overrides a recessive allele when it comes to expressing itself in the phenotype of the rabbit.

 

Below you will see an example of how basic gene inheritance works with two alleles in the "A series" of rabbit color genetics. The sire passes along one allele within the series, as does the dam.  Each allele within the series has a 50% chance to be passed along.  The alleles in this example are variants on the A gene. They are "A" and "a". (You will learn what these represent in the next section).

basicinheritance.jpg

To illustrate how these genes are inherited, we use what are called Punnett Squares.

First, you put the Sire's genes along one side and the the Dam's genes along the other.

 

It doesn't matter which side you put which on, as long as you are only using genes from the same gene series.

 

We'll continue using two alleles from our "A-series" of genes.

punnet1.jpg

Since each parent contributes one allele to each offspring, we will see that when we put each gene in the corresponding box within the Punnett Square.

This means that each box contains one allele from each parent in all possible genetic combinations.  Understanding orders of dominance within each series will come later, just understand that the more Dominant alleles are typically capitalized.

 

Within the A-series, "A" is dominant over "a", which means the "A" allele is expressed physically over the "a" allele, so we write the order of the alleles as "Aa"  This is also known as a "heterozygous" gene series.  When you have two alleles of the same gene it is referred to as a "homozygous" gene series, where neither gene is dominant over the other.

punnet2.jpg
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You can use this information to calculate the percentage chance for each offspring to carry a specific set within that gene series.  It doesn't matter which parent contributed which allele, since the probability is only affected by the amount of squares each UNIQUE pairing occurs in.

Using our example, you can see that out of the four squares, the unique gene sets are "AA" (appearing one time), "Aa" (appearing twice), and "aa" (appearing one time).

punnetts4.jpg

This can become more complicated as more alleles are introduced within each series, however the PROCESS of figuring out gene inheritance is still the same.  One parent can be "A a" and the other "a a", and you would still fill out the punnet square in the same fashion, but you would get a different spread of inheritance chances.

To learn more about how we apply this to Rabbit Color Genetics, go to the NEXT SECTION ==>

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