Post by sandy on Feb 16, 2006 23:18:38 GMT -5
Oh boy... I'm slogging through this and it's slowly starting to sink in. Here's a question I asked of a person working at the Animal genetics lab in Fla. He's been emailing with me and is very helpful!
My question to him:
I do have a few more questions. You mentioned the "recessive red allele." I'm not really sure what the term "allele" is referring to. Is it different than a gene, or is it another word for gene... perhaps the more technical, scientific word for gene?
I've also been reading about the Extension Locus: *"**In the case of the two Base Colors, red and black, these are both determined at the same place (Latin term "locus" plural "loci") on the DNA strand. This "Locus" is called the Extension Locus, and it is signified by the letter "E". The dominant form, black, is called "E" and the recessive form, red, is "e"."*
I've seen this "Extension Locus" mentioned several times and it's not quite sinking in as to what it is. At first I thought it was a place on the DNA strand geneticists identified as carrying the red and black gene, but now I'm not sure, because there are other places on the strand identified with certain genes, and I've never seen names for those places. So, what (or where???) is this Extension Locus? Is it a "spot" that will have both the black and red genes, or only one or the other?
Anudder question on dominant and recessive genes: Red is recessive, black is dominant in equine color. If a sire is red, can he still carry a black, dominant gene? If he CAN carry a black, dominant gene, then why is he red if the black is dominant?
I assume one animal can carry both a red AND black gene?
And his answer:
Hey Sandy,
A gene is basically a section of an individuals dna that encodes for something. A horse carries two copies of each gene inheriting one from the mother and one from the father. Sometimes the word gene is used to describe a disease or condition such as the gene for obesity. A locus is a particular area of interest of a gene and an allele is the different possible coding at that locus.
Take for instance the Extension gene. The Extension gene is a particular gene that has been found to encode for red or black pigment of the horse. "Extension" is just the name for that gene. Research found an area, a single mutation, within this gene that determines if the coat will have a red or black base. There are two possibilities or alleles this area can have. Either "E", the dominant black allele, or "e" the recessive red allele. Since a horse has two copies of the gene, the possible coding at the Extension locus or gene can be EE (two copies of black), Ee (One of each) or ee (two copies of red). The dominant form of an allele will be the one that is expressed if both are present. The only time the recessive red will be expressed is when the horse is "ee" and does not carry the black allele. So to answer your question, no a red horse can not carry black. But a black horse can carry red.
So a "Ee" horse will be black but it does carry a copy of the recessive red "e" allele. This red "e" allele does not encode for the horses color but it can be passed on to it's offspring. When this Ee horse is bred, it will pass on one copy of each gene to the offspring and it's mate will supply the offspring with the other copy. Therefore, there is a 50% chance the "Ee" horse will pass on the "e" allele to the offspring. Now if the mate also passes on an "e" allele to the offspring, the result is "ee" for the offspring and its color will be red.
Let me know if this made sense."
So, I think it is starting to make sense. Of course I have a lot of other questions I'm going to be asking him. This is really fun!
*It's so nice to have a geneticist in the house* haha
sandy
My question to him:
I do have a few more questions. You mentioned the "recessive red allele." I'm not really sure what the term "allele" is referring to. Is it different than a gene, or is it another word for gene... perhaps the more technical, scientific word for gene?
I've also been reading about the Extension Locus: *"**In the case of the two Base Colors, red and black, these are both determined at the same place (Latin term "locus" plural "loci") on the DNA strand. This "Locus" is called the Extension Locus, and it is signified by the letter "E". The dominant form, black, is called "E" and the recessive form, red, is "e"."*
I've seen this "Extension Locus" mentioned several times and it's not quite sinking in as to what it is. At first I thought it was a place on the DNA strand geneticists identified as carrying the red and black gene, but now I'm not sure, because there are other places on the strand identified with certain genes, and I've never seen names for those places. So, what (or where???) is this Extension Locus? Is it a "spot" that will have both the black and red genes, or only one or the other?
Anudder question on dominant and recessive genes: Red is recessive, black is dominant in equine color. If a sire is red, can he still carry a black, dominant gene? If he CAN carry a black, dominant gene, then why is he red if the black is dominant?
I assume one animal can carry both a red AND black gene?
And his answer:
Hey Sandy,
A gene is basically a section of an individuals dna that encodes for something. A horse carries two copies of each gene inheriting one from the mother and one from the father. Sometimes the word gene is used to describe a disease or condition such as the gene for obesity. A locus is a particular area of interest of a gene and an allele is the different possible coding at that locus.
Take for instance the Extension gene. The Extension gene is a particular gene that has been found to encode for red or black pigment of the horse. "Extension" is just the name for that gene. Research found an area, a single mutation, within this gene that determines if the coat will have a red or black base. There are two possibilities or alleles this area can have. Either "E", the dominant black allele, or "e" the recessive red allele. Since a horse has two copies of the gene, the possible coding at the Extension locus or gene can be EE (two copies of black), Ee (One of each) or ee (two copies of red). The dominant form of an allele will be the one that is expressed if both are present. The only time the recessive red will be expressed is when the horse is "ee" and does not carry the black allele. So to answer your question, no a red horse can not carry black. But a black horse can carry red.
So a "Ee" horse will be black but it does carry a copy of the recessive red "e" allele. This red "e" allele does not encode for the horses color but it can be passed on to it's offspring. When this Ee horse is bred, it will pass on one copy of each gene to the offspring and it's mate will supply the offspring with the other copy. Therefore, there is a 50% chance the "Ee" horse will pass on the "e" allele to the offspring. Now if the mate also passes on an "e" allele to the offspring, the result is "ee" for the offspring and its color will be red.
Let me know if this made sense."
So, I think it is starting to make sense. Of course I have a lot of other questions I'm going to be asking him. This is really fun!
*It's so nice to have a geneticist in the house* haha
sandy