I really need some help and guidance.
I need some internet references to a guide for genetics for dummies. Or maybe there is a person on P&L and that person would want to teach us all some genetics lingo and information.
I am wanting to try starting a project for a new color of orpingtons, but I know nothing about genetics or even where to get started. Everything I look into is way over my head.
Someone please help.
Sheila
This message was edited Mar 5, 2009 12:57 AM
Genetic for Dummies
What color are you looking to breed for and is it seen at all in the breed?
Sheila -I found a couple of good starter links last night and put 'em in that first post on the reference thread, under genetics. One is a really nice beginner thing, for me anyway...I read and forget it all repeatedly, lol.
edited - something odd happened to my post....that took me an hour to write....dangummit....
This message was edited Mar 1, 2009 2:39 PM
trying again...
BASIC GENETICS!
Ok, I’m going to try to make this simple, simple, simple. If anyone wants to argue the finer points of genetics, please d-mail me! I realize there are exceptions to much of what I am about to say. I have an MS in genetics so I am not clueless! There is no “easy” way to explain genetics but I’m doing my best here to make something folks can understand. This is my attempt at giving a basic genetics lesson without overloading anyone. If it’s too simple, let me know, and we’ll get complicated!
Inside a cell are structures called chromosomes. A chromosome is a big long “chunk” of DNA that is tightly twisted into a specific structure. All the DNA that makes up a single chromosome could contain hundreds or thousands of genes. It also contains a lot of DNA that we don’t know the purpose for (sometimes called “junk DNA” but it’s not really junk, we just don’t know enough about it yet). Inside a chicken cell, there are 78 chromosomes, while a human cell only has 46 chromosomes. They come in pairs. So, a chicken has a pair of chromosome 1, a pair of chromosome 2, etc all the way up to chromosome 39.
Because you (or a chicken) have 2 copies of every chromosome, you have 2 copies of every gene. One copy of each gene came from your mom, and one copy came from your dad. Down to basics, every egg cell and every sperm cell only has 1 copy of each chromosome. This is called a haploid cell. When the two come together, they make a diploid cell. A cell with 2 copies of every chromosome is a diploid cell. Most of our cells are diploid.
So, with chickens, the rooster gives 1 complete set of chicken genes (on chromosomes) to the baby chick, and the mother gives 1 complete set. Each gene can have multiple forms, and this can get really complicated, but for this simple outline, let’s say there are two forms: dominant and recessive. Dominant means that the dominant gene will “mask” the recessive gene. So for colour, let’s just say, that purple feathers is dominant over green feathers.
A chicken could have 2 copies of the purple dominant gene like this: PP. That chicken is purple.
A different chicken could have 1 copy of the purple dominant gene, P, and one copy of the recessive green gene, g. So they would have Pg, but the purple is dominant over the green, so they are purple too, but they carry the green gene.
A 3rd chicken could have 2 copies of the green gene, gg. That gene is recessive, but there is no purple gene to mask it. Therefore, that chicken is green.
When you have two copies of a gene that are the same, like PP or gg, it’s called “homozygous” for that trait. When you have two different copies, like Pg, it’s “heterozygous”
So, let’s do some chicken sex!
PP rooster (purple) meets gg hen (green) and they have babies. All babies get one gene from mom and one gene from dad. They each get a P gene from dad, because that’s all he has to give. They also each get a g gene from mom, because that’s all she has to give. All babies are therefore Pg. So, the parents were homozygotes, the babies are heterozygotes. They are all purple though, so you might think they were PP, but they are all carrying the green gene.
What happens if two of the babies mate?
Pg x Pg (we use x symbol to show mating crosses)
Each baby gets a P or a g from mom, and another P or g from Dad. Soooo….how do we figure this out? Easiest way is with something called a ‘punnett square.’
You put the one parent’s genes along the top, and the other’s along the side, like this:
------P------g
P
g
Then you fill in the squares for the possible combinations, by using the letter from the row and column that you’re in, like this:
-------P-------g
P-----PP-----Pg
g-----Pg------gg
Ah-hah! So, we have 25% of the babies will be PP (purple homozygous), we have 50% of the babies will be Pg (purple, heterozygous) and we will have 25% of the babies being gg (green, homozygous.
This 25/50/25 ratio is very common in offspring.
Another common ratio is 50/50, which you get from breeding a homozygote to a heterozygote, like this:
-------P-------g
g-----Pg-----gg
g-----Pg-----gg
So there, you would have 50% Pg (purple) and 50% gg (green).
So, the trouble is, that very few traits are controlled by only one gene. For example, last I heard, I think there are 20-something genes involved in human eye color, which is why occasionally brown eyed people have a blue eyed baby, etc. Same with hair colour, and of course, same with feather colour. There are MANY genes involved.
So, to start a breeding project, you should ensure that you are starting with parents that are homozygous for the trait of interest. That means they are not carrying some recessive genes that will introduce bizarre results into your breeding. How do you know if the parents are homozygous? The only way is to breed them, and to ensure that you see 100% of the offspring having the trait, and THEN breed the offspring, and ensure you see 100% of the trait again. Only that way will you be able to determine which genes are being carried by which birds. Let’s say black is dominant over white, and you start with a pair of birds (one black, one white, but the black carries the white trait but it’s masked because black is dominant), you will get completely different offspring than if you start with a black homozygote bird and a white homozygote bird. In the first case, you won’t know which babies carry which genes, but in the second case you will. In order to ensure good record keeping and knowledge of which bird has which gene, the latter is highly preferable.
I hope some of this helps, just trying to teach some basics!
Claire
p.s. Usually the dominant and recessive copies of a given gene are represented by the same letter, P and p. I used P and g for simplicity, but if you are reading other materials, you will see Pp or Gg for example.
This message was edited Mar 1, 2009 5:01 PM
Oh my gosh, Ms. Moxon. Can you tell me when the next class meets. You are now elected the official Dave's Garden Genetics teacher.
I guess what I also am confused about is when I read information. People are using so many letters. I am sure the each letter represents something ie color, comb type, shank color, but I have no idea what these letters are referring to and therefore have no idea what they are talking about. Do certain letters represent certain things in chickens?
Sheila
Teacher! Teacher!
I am confused--but I also have a blinding headache so I may be easily confused--In the final paragraph you say it is best to start with birds that are heterozygous for the trait of interest. But then in closing you say that it is preferable to start with homozygous birds. I would have thought the latter....
I'll sit down in my seat again...ohhhhhmyhead........
Claire,
I'm so glad you posted that and not me LOL. Shelia, that's why I asked what trait (Color) you are looking for. I breed Paint Horses so the color idea is familiar to me. Remember Heterozygous means different and homozygous means same. Sometimes homozygous (at least in horses and Manx cats) dominate can be lethal. Also, when you you are breeding specifically for one trait you must breed again and again and in the process you limit the gene pool. Also, at least with horses, they have found recently that a horse can genetically carry the color information but the gene that "expresses" shows the color is "turned" off. So the individual may carry the color gene but not show it. So what color are you going for again?
Lisa
Sheila - my genetics was all plant genetics, so I'm no specialist on chicken genetics, but I do understand the basics because they're pretty much the same for any living thing. Generally each letter represents a gene. There may be 1 or more genes that correspond to a trait (like green eggs for instance, which I understand requires some "blue" genetics and some "brown" genetics mixed. There is no single green egg gene).
So for example, on this page here: http://www.pekinbantams.com/genetics_two_two.asp
in the first table they are talking about chick down colors. The E is the dominant color form. The e+ and e^ and all the others with the superscript letters are different recessive variants of that same gene. When I did my example, I just had 1 dominant and 1 recessive gene, but usually there is 1 dominant and a whole bunch of recessives, and some of the recessive forms may be dominant over other recessive forms, but not AS dominant as the original dominant form. Like A is dominant and a+ is recessive but is still dominant over a*. So AA and Aa+ and Aa* will all look the same. a+a+ and a+a* will look different from the first group, but the same as each other. a*a* will look different from all the others.
I imagine the same letters are typically used for certain traits, but I don't know them right off hand.
Like 1lisac said, there can be lethal combinations, and I think that's the problem with the true Araucanas and why they are so hard to breed. I think the embryos die due to the lethal gene combination.
Catscan - THANK you! You got me! That was my second time writing that thing up and I was getting tired. Yes, definitely start with homozygous parents.
You Go Gals!! I lose my mind trying to figure out the alternative life form recessives...them weird diacriticals.
Just to prove Claire's point when you cross a grey poodle with an apricot one you get Blk/wht offspring! Shelia, What color are you trying to get? I would breed 2 that have some form of the color that you are trying to get and go from there.
Maybe Sheila wants to keep her color goal secret, so that we don't all try to do the same thing. That's OK. :-)
Example - Sheila wants green orpingtons. Blue orpingtons crossed with yellow orps gives green orps (in theory).
MAKE SURE you start with a homozygous blue orp and a homozygous yellow orp, so you don't get mixed recessive genes in there throwing off your party. Unless you want that kind of party!! But then the records will be really tough because you'll get some super-cool bird and have no idea what the genetics of the parents are that produced it, and you'll have to just keep trying to re-create that match by chance, rather than by following the same recipe.
"MAKE SURE you start with a homozygous blue orp and a homozygous yellow orp"
And for the purpose of keeping this a learning thread, How, one might ask, would I MAKE SURE?
Tell me Claire: When my dad used to call me a dip, was that short for diploid? Claire that was a great explanation, but oh am i so confused. I thinks me shall only hatch eggs that are fertile and wait and see what the out come is.LOL Hay
Breed, Hatch, Repeat.
OH Claire! I love it! You explained it so I can actually remember! Bless you! I had some of that info in that air space of a brain I have, but I couldn't bring it out.
This is so cool.. Thank you so much!
Not that I'm gonna go make a green Modern Game, but I now I know how! LOL
Care to tell a duffer (after all that typing trauma) how to map back from offspring? And keep it that simple? The RIR genes from my BSLs that crossed to the BJG keep showing up in odd places. Got a BR cross that has red glints on hackle and saddle feathers. Came from his paternal great grand hen...who was pure RIR...so she claims...
Fran - good question.
Let's say B is blue dominant gene, and small b is recessive, white.
BB chickens are blue
Bb chickens are blue
bb chickens are white
You'd have to breed the homozygous blue to another homozygous blue and then breed their babies (preferably multiple times). If they are both homozygous blue, here's how it would go:
BB x BB = all BB babies.
BB baby x BB baby = all BB (blue) babies, confirms homozygosity of both parents.
So why did I say breed the babies multiple times? Well, imagine....
...if you had a homozygote BB and a heterozygote Bb, here's how it would go:
BB x Bb = half BB babies, half Bb babies (but all blue because B is dominant over b)
Bb baby x Bb baby = 25% BB, 50% Bb and 25% bb babies. The bb babies would be white, so you'd know you had a non-homozygote parent.
***Unfortunately****, you could also pick 2 babies from the BB group, or one BB and one Bb, and still have all blue babies, and *think* that you had a homozygote parent when really you don't. This is why multiple breedings of the babies would be preferable - to account for any potential heterozygotes.
Then you do the same thing with the yellow ones.
Then, when you know you've got 2 homozygotes, you can breed them and know exactly what all the babies will be from the first pairing, and then once you breed those babies, you can tell (based on the 25:50:25 or 50:50 ratios) whether they are hetero or homo.
Bottom line - ensuring that you have homozygous birds is not easy or fast. If you had access to a reputable breeder who had been breeding the same birds repeatedly with the same results every time, preferably someone who has an interest in, and understanding of genetics, you might be able to obtain homozygous birds from the start.
Umm. I think I have zygo-conflicted birds...
Sorry Haystack, I tried to make it clear. I didn't want to confuse anybody. :-(
ZZ - glad to be of assistance, although I'm sure Catscan could have told you the same!
Grow - best way to have an idea of what you started with, based on offspring patterns, is to look at ratios. You have to have a bunch of offspring from the same cross. Do you see more of a 50:50 ratio, or a 25:50:25 ratio, in the trait?
50:50 is usually a BB x Bb type of cross. (or Bb x bb)
25:50:25 is usually a Bb x Bb type of cross.
100% the same offspring is either BB x BB or BB x bb.
BUT, remember, this is all assuming that a single gene is responsible for a colour trait, which is not really feasible in many cases. There are probably several, so even if there were two genes responsible...
...AABB or AaBB or aaBB or AABb or AAbb or AaBb or aabb are possible. When you start making Punnett squares from those kinds of crosses, things get messy and complicated in a hurry. And it's likely there are sometimes 5 or more genes involved. (i.e. AABBCCDDEE and all its variations).
This is why things sometimes don't show up in a couple of generations, and then suddenly do - because finally a cross has been made that allows a recessive trait to show up.
Of course, it gets more complicated, because there are things like leaky dominant genes, that are mostly dominant, but sometimes allow a recessive trait to show partially.
Ugh....
And it really gets messed up when you get other pairs of genes which affect things as diluters or intensifiers of colors and color patterns.
Really nice basic explanation!! Just about like my opening lecture on genetics in high school biology class. Only missing the comments from the class clown.
Robert
Thanks Patrob - it's been a long time since I was a TA for Genetics 101! I had that weird memory of a sea of blank faces looking back at me when I started doing meiosis.
Where is our class clown? Usually it's Grownut....
That's why I suggested that you breed 2 birds that have some form of the color that you want and see what happens. Because, as Claire mentioned, there is no way to tell if they are homozygous unless you breed them. With paint horse we do genetic testing on Stallions and usually use produced offspring in mares. We look for homozygous in color ie black, and homozygous in expression ie solid or colored. Even Mendall (when studying peas) first started out by breeding 2 different plants the significance of this crossing came later.
Claire, You say to BE SURE to start out with two birds that you know are homozygous, but the only way to be sure they are is to breed them and observe the offspring. I don't understand what you mean. It kind of sounds like the chicken and the egg ordeal.
Present and accounted for. Just feeling as though I had somehow fallen down on the job.
My prob. is that while I know pretty much what the crosses are I'm getting lost in dilutions --like spangles and lacing. My 3rd gen has me baffled as to how to map 'em. Though they do stay consistently black for female and flashy for males. The few decorations that show up on the females are interesting.
Probably shouldn't be concerning myself with the barring gene in Genetics101...
I forgot about chickens and sexual dimorphism, so whats good for the goose may not be good for the gander.
1Lisac - yes, I meant that she should start her attempt to get to the "new" color by starting with 2 homozygous birds, but she can't do that until she has already gone through some breeding cycles, unless she can obtain homozygous birds from some other source that is trustworthy. I didn't think she should start aiming for the new colour until she had established what the parent birds were (through test crosses). Sorry if I didn't make that clear.
So step 1: choose birds, test for homozygosity as best as you can (or obtain homozygous birds elsewhere)
Step 2: start breeding assumed homozygotes in specific repeatable crosses to experiment with offspring (and you will know what the offspring are because you will in theory know that the parents are homozygous), cross breeding of offspring, etc. I don't know much about the effects of inbreeding in chickens but it would probably be good to have 2 different, unrelated, homozygous birds of each sex (so that you can cross breed between populations, rather than always inbreed)
Step 3: If it all goes pear-shaped, the parents probably weren't homozygous.
Step 4: Start over. :-)
Another good point, 1Lisac. Although we could hope, faintly, that any such dimorphism would be recognizable and consistent over generations...
I really wish I had waited until morning to check this thread. This sexual dimorphism thing is going to have my head reeling. Most of my roos from stock that is "bred true" show colors that the plain hens never do. Horses are so much more straight foreward. So does this mean the colors are sex-linked in birds?
Claire-After I typed that post I thought that was what you meant, but I wasn't sure. Thank you for answering I didn't want to give the impression that I didn't agree with you I just didn't understand.
I might be able to answer that question for you. I think Lavender is the color she is trying for.
luvs are you giving away my project????????? I really don't know which way I would like to go. I had thought about a lavendar Orp or a golden laced orp
The gold laced would be harder in trying to get the lacing, though.
Sheila
oops sorry :(
This is the most interesting, understandable thread to come along in forever.. would be a GREAT sticky!
I do it the easy way i let other folks breed them and i buy them LOL
My advice is breed those that have the trait you like hatch, repeat and keep notes. Try to use unrelated birds when possible to increase your gene pool. You will see the effects of recessive genes more often when you breed related animals, but lavender may be recessive I don't know. I have explained genetics to many a horseman that didn't know how it worked but had a pasture of beautiful expensive horses, which proved to me that they already knew what they were doing, even though they had never been in a lab. There is more and more evidence that the environment can have a lot of effect on how genes are expressed so the phenotype (what the bird looks like) may appear different from its genotype (the genes the individual possesses). I don't mean to bore everybody but this is really interesting to me.
Lisa
I find it interesting even with out having the chickens.
Ok here is what I have, I have a blue andalusian cross to a buff orp, she shows more blue than buff her 2 sisters show more of the buff. I have a black a blue and a blue splash jg roo's. I have a lav jg pullet and a couple black jg hens. that is what i am going to play with. What ya think.
Oh Genetic wise i have Lemon Blues which are brown red crossed with blue splash so when i breed i can get blue splash,lemon blue and brown red. I have found the brown red to be dominate in these as i get more of those than i do the others.
I have blue mille fleur which give me blue mille fleur but can also just give me millie's. My crele are a cross of BB red and barred yet they only give me crele i have had no barred or bb's come from these.
My porcelain are complicated as they originated from a pair of millie's my friend owns these and the genetic makeup of this pair of millies he has is strange. I wish i could reproduce it but who could figure it out........This one pair of millie's produce's 4 different kinds of chickens it produces Millie, blue millie , porcelaine, and what he call sport millie's.
The genetic makeup of this one pair of chickens is amazing but i can't reproduce that here. My porcelains give me porcelain and the millies do the same.
tell me about the trying to figure it out. I go to read up on things and i get so lost. But how it has been explained here I can understand so much more.
I won't do the genetics thing the people who breed around here are like the mafia it's well kept secrets and smoke and mirrors LOL
I know enough to keep what i have going and thats good for me.