lesson 4: gene interactions
Key words:
-Codominance
-Incomplete dominance
-Epistasis
-Pleiotropy
So in previous pages, we've learned that a dominant allele masks a recessive allele, right? This is true in most cases, except where codominance or incomplete dominance involved.
Incomplete dominance is when the two different alleles in a hybrid blend together, and the resultant phenotype is halfway between the two. For example, an imaginary blue gene and yellow gene blend, making the offspring green. Codominance is when the alleles are both expressed individually. For example, an imaginary blue gene and yellow gene combine, causing the offspring to be blue with yellow spots. The distinction between codominance and incomplete dominance can get a little blurry, especially on the molecular level, so the terms can frequently be used interchangeably.
Here's an example of codominance. The wool, or, fuzzy gene is recessive, denoted by f. A rabbit with two of the fuzzy genes, ff, has wool fur. If a rabbit has two dominant, FF genes, then it has normal fur. A rabbit with Ff genotype has normal fur, but slightly longer and thicker.
They say a picture (or Punnett Square) is worth a thousand words, so here's an example for you:
-Codominance
-Incomplete dominance
-Epistasis
-Pleiotropy
So in previous pages, we've learned that a dominant allele masks a recessive allele, right? This is true in most cases, except where codominance or incomplete dominance involved.
Incomplete dominance is when the two different alleles in a hybrid blend together, and the resultant phenotype is halfway between the two. For example, an imaginary blue gene and yellow gene blend, making the offspring green. Codominance is when the alleles are both expressed individually. For example, an imaginary blue gene and yellow gene combine, causing the offspring to be blue with yellow spots. The distinction between codominance and incomplete dominance can get a little blurry, especially on the molecular level, so the terms can frequently be used interchangeably.
Here's an example of codominance. The wool, or, fuzzy gene is recessive, denoted by f. A rabbit with two of the fuzzy genes, ff, has wool fur. If a rabbit has two dominant, FF genes, then it has normal fur. A rabbit with Ff genotype has normal fur, but slightly longer and thicker.
They say a picture (or Punnett Square) is worth a thousand words, so here's an example for you:
All of the offspring would be Ff (fuzzy carrier), and be semi-fuzzy (slightly longer than normal) in phenotype.
Next let's talk about epistasis. Epistasis sounds scary, but it's really quite simple. Basically, an epistatic gene is one that is able to mask another gene. The other gene is still there but is not expressed. A great example of this is the REW (ruby-eyed white) gene. It is recessive, denoted by cc. When a rabbit carries the REW gene (Cc), the REW gene is not expressed. However, when a rabbit is homozygous recessive cc, this masks ALL the other color genes. So the rabbit may genetically be a chestnut, a blue, a pointed white, a broken orange, or any other color UNDERNEATH the REW gene, but that color is not expressed because the REW gene has 'blocked' it.
Pleiotropy is when one gene results in multiple, seemingly unrelated effects. For example, rabbits that have two copies of the broken gene (EnEn) are known as Charlies. Animals with this genotype are minimally marked brokens with distinctive nose markings, but they also very frequently have 'megacolon,' a digestive disorder that is extremely rare in normal broken or solid animals. Interestingly, megacolon is not completely penetrant, meaning not all rabbits with this genotype present with the disorder.
That's it for now! Hopefully this has given you a better grasp on basic genetics to better understand my other articles. :)
Next let's talk about epistasis. Epistasis sounds scary, but it's really quite simple. Basically, an epistatic gene is one that is able to mask another gene. The other gene is still there but is not expressed. A great example of this is the REW (ruby-eyed white) gene. It is recessive, denoted by cc. When a rabbit carries the REW gene (Cc), the REW gene is not expressed. However, when a rabbit is homozygous recessive cc, this masks ALL the other color genes. So the rabbit may genetically be a chestnut, a blue, a pointed white, a broken orange, or any other color UNDERNEATH the REW gene, but that color is not expressed because the REW gene has 'blocked' it.
Pleiotropy is when one gene results in multiple, seemingly unrelated effects. For example, rabbits that have two copies of the broken gene (EnEn) are known as Charlies. Animals with this genotype are minimally marked brokens with distinctive nose markings, but they also very frequently have 'megacolon,' a digestive disorder that is extremely rare in normal broken or solid animals. Interestingly, megacolon is not completely penetrant, meaning not all rabbits with this genotype present with the disorder.
That's it for now! Hopefully this has given you a better grasp on basic genetics to better understand my other articles. :)