Genetics Primer

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Farrier1987
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Genetics Primer

Post by Farrier1987 » Wed Feb 24, 2016 5:05 pm

Hey folks. I need a little help, (well according to some, a LOT of help). I know there are those here have way more expertise than I on genetics. Could someone do a short primer please? Like what is an F1 and F2. Or for an example, silkie has five toes. What are the chances that a crossbred offspring will have four or five toes? Can the offspring of a four toed crossbred have five toes, even though both parents had four toes? Where do dominant and recessive come in? That kind of stuff?

I know there is the web and libraries, and I can do research and all and I understand a little about probabilities. But it would be nice to ask someone who understands this subject well to expound a little on it, and then I can ask questions back. Thanks.
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Farrier1987. South of Chatham on Lake Erie. Chickens, goats, horse, garden, dog, cat. Worked all over the world. Know a little bit about a lot of things. No incubator, broody hens.

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JimW
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Genetics Primer

Post by JimW » Wed Feb 24, 2016 6:27 pm

F1 stands for First Filial Generation, F2 is Second Finial Generation... So say your have a group of chickens you are raising up for breeding stock, those first birds you breed are your P1 generation, Parent Generation. The offspring of those birds are your F1 generation. If you then took 2 birds from your F1 generation and bred them their offspring is the F2 generation.

I know nothing about silkies so can't help with the 5 toe thing. I have Houdan chickens that have 5 toes and last year ended up with a few houdan crosses (no idea what they were crossed with) and the crosses have 5 toes, those the 5th toe was often smaller.

Dominant and recessive is one way traits can be inherited. Not a chicken example but if you look at albinism (lack of dark skin/hair pigments) in many species albinism is a recessive trait, so to show the albino phenotype (outward appearance) and individual most have 2 copies of the gene (called allele) for albino. If an individual had 1 gene for normal colour and 1 gene for albino, that individual would look normal coloured but can pass the albino gene to it offspring.

If we let "N" represent normal colour and "n" represent albino and we cross a normal individual with no albino genes (NN) with an albino
nn), this is P1 generation, all the F1 generation would have 1 normal colour allele and 1 albino allele (Nn), this is called heterozygous. Since albino is recessive the an individual with 1 normal and 1 albino gene would look normal coloured, but all carry albino gene.

If we the breed 2 F1 generation individuals together Nn x Nn

then we would end up with 25% of the offspring (F2) being albino (nn); 50% being normal but carry albino gene (Nn) and 25% being normal with no albino gene (NN).

For traits that are recessive you cannot tell the difference between the individuals that look normal with no albino gene (NN) and the normal coloured ones with the albino gene (Nn), and as a result suprizes can show up when breeding if the source/genetics of your breeding stock in unknown.

Not all traits are simply recessive or albino, some are incomplete dominance, so and individual with 2 different alleles would be a 3rd phenotype. For example black (BB) cross white (WW) gives offspring with 1 allele for each colour appear grey (BW).

Other traits are co-dominate, where black cross white would produce individuals with black and white fur or feathers.

Other traits are sex-linked where the gene for a trait is on a sex chromosome so males and females will look different.

That is grade 11 Biology Lesson #1. Let me know when you are ready and I can send you the quiz I give my biology students. lol

JimW
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JimW
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Genetics Primer

Post by JimW » Wed Feb 24, 2016 6:30 pm

Here is a good link about chicken genes.

http://sellers.kippenjungle.nl/page3.html
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Keeping poultry with my 2 daughters since 2014.
Ayam cemani, BC Marans, Legbars (Gold Crele, Opal and White), Mosaics, Hmongs and Cuckoo Malines
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thegawd
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Genetics Primer

Post by thegawd » Wed Feb 24, 2016 7:28 pm

I stickied this, theres already a lot of great info in this thread, thanks Jim! and I have a feeling that there is more to come.
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Cuttlefish
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Genetics Primer

Post by Cuttlefish » Wed Feb 24, 2016 7:40 pm

Chicken color genetics can be quite complicated. If you don't have a good grasp on the terminology consider starting with human basics. This video goes pretty fast, but it'll get you up to speed to enjoy the kippenjungle site. : )
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Genetics Primer

Post by Chicken Ninja » Wed Feb 24, 2016 7:59 pm

I believe that the polydatyl (5-toes) gene is dominant, like brown eyes in humans. But it could be that it can be diluted by the short-toe gene to get a shorter 5th toe, like Jim described.

A really good idea to start wrapping your head around for genetics is the black/blue/splash phenotypes (how the bird looks):

So you have a black bird: It has two dominant black genes that make the bird look black -> BB
A blue bird, which is basically a washed-out black, has only one dominant black genes, and a recessive dilutor gene -> Bb
A splash bird is a pale grey with random black and blue feathers, has two recessive dilutor genes -> bb

So each parent can only give one of these letter to each offspring. So two black birds, only have dominant B genes between them - all chicks are black, and called homozygous dominant, becasue they only have the dominant gene.

Two blue birds have 2 dominant B and two recessive b genes between them. Chicks can get a B from each - black (BB) chicks, a B from one parent and a b from another - blue (Bb) chicks, or a b from both - splach (bb) chicks. All blue birds are called heterozygous because they have a dominant and recessive gene.

Two splash birds only have recessive b genes to give offspring, so all chicks are also splash, and called homozygous recessive, because they only have the recessive gene.

Crossing the different colours cretes new probibilities! 2 black birds = 100% black chicks. 2 blue birds = 25% black, 50% blue, 25% splash. 2 splash birds = 100% splash.
Black/Blue = 50% black, 50% blue. Blue/Splash = 50% blue, 50% splash
Black/Splash = 100% blue.

The BBS (Black/blue/splash) colour genetics are one of the simpler types to wrap your head around, and once you understand how the different colours are created, it becomes easier to understand other types like sex-linked, liked genes, etc.

Hope this helps Farrier1987! Keep asking questions, and you'll get it!
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JimW
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Genetics Primer

Post by JimW » Thu Feb 25, 2016 8:35 pm

Just found this while I was playing around on the internet....

https://scratchcradle.wordpress.com/gen ... ni-series/
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Keeping poultry with my 2 daughters since 2014.
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windwalkingwolf
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Genetics Primer

Post by windwalkingwolf » Thu Feb 25, 2016 10:25 pm

I just saw that one too, Jim, I like it. It doesn't make me go crosseyed :D
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WLLady
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Genetics Primer

Post by WLLady » Fri Feb 26, 2016 10:35 am

and farrier: take your time absorbing it....it's not easy....because not all genes act the same. some are dominant (cover other ones up), some are recessive (you need two, and commonly also need the absence of some others and modifiers that could cover it up), some are modifiers (that take the effect of one gene but alters it just enough to make it appear different).....

the easiest one (i found) was to start with is the e locus. it dictates mainly what the coat colour and pattern is of the chick. so it will dictate if your chick looks like a penguin, or is plain yellow or orange or brown chipmunky with stripes. it also dictates the overall pattern in where on the bird certain colours can be expressed (ie, eWh gives black tips on wings and tail, with a base lighter colour all over breast, back etc in the female, cinnamon wing triangle in male, less black hackle striping in boys etc etc). this is kind of the frame work that all the other genes build on...

you have genes. these are the things that code for stuff....like blue eyes. or brown eyes. or yellow legs. where these genes are in the DNA is called the "locus". one gene is located at one locus. where this is a little more complicated is there's 2 copies of everything. so when we say that the e locus is e+/e+ there's 2 copies (because there are 2 chromosomes...each with the same e locus or place on the chromosome and each locus gets one gene, therefore 2 genes total in that animal) of e+, one on each of the chromosomes that make up the pair that house the e locus. this chick will be a chipmunky striped looking chick. if the genes located on each of the chromosomes at that locus were E, then you get a black chick. Now, there are several different mutations within one gene at that locus. the wildtype one is e+....mutate that and you can get E, or eWh (wheaten) or eb....it was originally the SAME gene coding, but something in the coding got changed, and then because it is changed its a mutation in the gene and was given a unique name, E, ER, eWh, eb...etc. each tiny change in the gene (the mutation) results in a different coat pattern/colour in the chicks.

So it is totally possible to have a bird with an e locus that is E/Ewh. This chick would be black because E is dominant over Ewh (or one could also say that Ewh is recessive to E). So even though both the genes are there, one on one chromosome and the other on the second chromosom, the expression of Ewh is overridden and hidden by E. now....if you get e+/Ewh it's a little more complicated, because Ewh is not totally dominant to e+ and e+ is not totally dominant to Ewh. so some chicks end up looking yellow or orangy with broken striped down their backs - the yellow all over is the Ewh, but the e+ donates some stripes, it forces the expression of some of the striping normally seen. This is incomplete penetrance of the e+ over Ewh. it kinda happens, but not all the way, but it's not covered up either.

and that's probably enough for now....LOL. yes, please ask away, we'll all do our best!!!!

do you have a specific breeding you are thinking of doing and wondering how it will come out? each case is a bit different depending on where those birds come from and what genes they have already etc etc-oh and about your other question you asked me on the weekend, i've PMd you the information i have, and if you PM your email to me i'll send you a bunch of documents i got from the hospital/university.
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Poultry Genetics, An Introduction, Article of the Day

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