Sexlinked Breeding

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Sexlinked Breeding

Postby tessg » Fri Jul 31, 2015 11:29 am

I understand that you can breed the likes of a RIR Rooster over a Barred Rock hen to get sexlinked chicks at hatching. BUT why doesn't it work with the opposite, i.e. a Barred Rock roo over a RIR hen?? I'm just curious to know.
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Re: Sexlinked Breeding

Postby seatil » Fri Jul 31, 2015 12:22 pm

I'm sure a gazillion people could explain this more clearly, but I'll give it a go. Hopefully I don't get anything too wrong!

This is a sex-linked trait and is carried on the sex chromosome. A chicken has a pair of sex chromosomes; either WZ (hen) or ZZ (rooster). The W chromosome is a bit deficient compared with the Z. It may be easier to think of each of these as a length of string, the W string being 10cm long and the Z being 20cm long. You can pin much more information to string 20cm long than 10cm long.

For the purposes of picturing this, the sex-linked barring gene (B) sits about 15cm along the Z chromosome. It's "fallen off" the end of the string on the W chromosome; basically meaning there's nothing there.

A hen (a Z and a W chromosome) will either be: B/- (barred) or b/- (not barred). The - represents where the gene "fell off the string" on the W chromosome, and what the hen looks like is entirely dependent on what she has on the Z chromosome.

A rooster (two Zs) will either be: B/B (very barred), B/b (barred) or b/b (not barred). What the rooster looks like is affected by both of his Z chromosomes, hence the barring being "barred" rather than "very barred" when he is B/b.

Hopefully I haven't lost you so far!

A RIR rooster will be b/b (not barred). A barred rock hen will be B/- (barred).

To work out what the offspring look like, we use something called a punnet square to work out all the possible combinations of offspring from the genes we're interested in. Offspring get one of a pair of genes from mum, and the other of the pair from dad.

Image

I've put mum's genes across the top, and dad's genes down the side. From this we can see that there are only two possibilities of offspring:

* b/B (male, barred)
* b/- (female, not barred)

If I repeat the punnet square with a barred rock roo (B/B) and a RIR hen (b/-):

Image

* B/b (male, barred, same as b/B).
* B/- (female, barred)

Hopefully that illustrates why you need the rooster and the hen the correct way around.

As a side note, with a RIR roo and a barred hen you may also have some indications of sex from the gold/silver gene which is also sex linked. I'm not sure how visible the effects of this gene are when barring is present, but in theory a RIR roo and barred hen will produce "gold" female offspring and "silver" male offspring, so putting the two together, you'd theoretically be getting gold* non-barred females and silver barred males.

[*] To further complicate things, this gold will be more like the mahogany colour of the RIR as the chicks will all get a dose of the autosomal (non-sex linked) mahogany gene from dad, which is dominant and turns the orangey gold into the deeper mahogany red of the RIR.

Still awake? :)
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Re: Sexlinked Breeding

Postby Kracka » Mon Aug 03, 2015 1:27 pm

:lol: still awake!
that's brilliant - I remember my genetics stuff we were taught at school (many many moons ago) - the thing to remember is poultry are the opposite way round (as you say) - roosters carry the double up (both full length 'strings') and the hens don't - opposite way round to people/mammals
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Re: Sexlinked Breeding

Postby sewren » Tue Aug 04, 2015 12:52 pm

Love the punnet squares!! :lol: :lol: Great explainable though.
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Re: Sexlinked Breeding

Postby joeyh » Tue Aug 04, 2015 6:16 pm

You're a bundle of knowledge, seatil! Thanks heaps!This was a very interesting read!
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Re: Sexlinked Breeding

Postby AlisonS » Wed Oct 28, 2015 9:36 am

I was searching for posts on sexing BR chicks and found this post - cool ços I'm (hopefully) hatching some Langshan/BR eggs just now. My hen is the BR, so I can see that any barred chicks will be roosters and all the pullets will be solid coloured. Now I'm not so sure about letting them hatch with my full Langshans, because the pullets might not be distinguishable from each other! I wonder how strong the Langshan leg feathering gene is. Maybe if they have feathered legs they're Langshans and if they're clean legged they're Xs??
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Re: Sexlinked Breeding

Postby seatil » Wed Oct 28, 2015 10:00 am

I would hatch them separately. The feathered leg gene I have floating around is incomplete dominant - a dosing effect thing. Two copies = really feathery feet, one copy = somewhat feathered feet, which seems to vary in degree from chook to chook.

I wonder how gangly legged your crosses will be compared with the purebreds :lol:
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Re: Sexlinked Breeding

Postby Kracka » Wed Oct 28, 2015 10:06 am

are the eggs in an incubator? if so, can you rig up a fence (when they go into the hatching tray) and divide the eggs, you'll get a bit of time to see who is who before they start climbing over hopefully
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Re: Sexlinked Breeding

Postby AlisonS » Wed Oct 28, 2015 1:01 pm

No, unfortunately for keeping them separate, they are under a hen. They may or may not be being sat on, as she hopped off this morning once she heard me feeding the others. I transferred her last night from the empty nestbox in the chook house to a nice cosy rabbit hutch and pile of eggs. She settled down happily and covered the eggs, but once she woke up and found the food she wanted to go back to her original nest. I've shut her in the nest part and blocked off the door to the run, so hopefully she's settled down on the eggs. I'm at work, so we'll find out when I go home, I guess.

Maybe I'll just keep all the eggs together now that they've started incubating, and only breed from the really feathered footed girls. Even supposing anyone hatches!
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Re: Sexlinked Breeding

Postby Kracka » Wed Oct 28, 2015 1:37 pm

I'm wondering what I'll come home to - a hen hatched chicks a couple of days ago, but she left one behind, found it cold & barely able to blink, popped it in the incubator, up on its feet this morning. So I tried giving it back to her, but found it cheeping loudly being ignored, so I've put it under another sitting hen (think her eggs are duds), but chick is a blue/black Silkie and she's a Buff Pekin, just hoping she's not fussy about what babies look like!
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Re: Sexlinked Breeding

Postby AlisonS » Thu Oct 29, 2015 1:21 pm

This going to work lark puts a real handbrake on the chook rearing!! I came home to my little broody sitting [i]next[i] to the pile of eggs with just three under her. :x She was glaring at me - if a chook can be said to glare! I let her out for breakfast this morning and she zoomed back to the chook house afterwards. I've shut her back in the dark with the three eggs she sat on over night... I don't hold out much hope that we'll have a hatch!! So no worries over unstriped Langshan crosses. :(

As for different coloured chicks - you'll be finding out after work, too! Hens are all individual, aren't they. I have one who's just desperate to be a mum and will accept chicks of all descriptions. She wants to mother them for ever - even when they're bigger than her. Once I put day old chicks under her when she'd only been broody for 2 days! In fact that's her and them in my avatar.
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Re: Sexlinked Breeding

Postby Kracka » Thu Oct 29, 2015 1:56 pm

I came home to a 'despatched chick' (hole in the head) :(
next two chicks in the incubator hatched (I picked up abandoned eggs) so I put them under a Blue Pekin - I know my blues are racist, babies have to be tones of blue/black/splash & luckily these two are... they all looked happy this morning when I left them, fingers crossed.
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Re: Sexlinked Breeding

Postby sewren » Thu Oct 29, 2015 3:23 pm

Oh no - sorry to hear that Alison :( Did you try to stick the eggs back under her at all? They might be ok, although I've read that in the early stages of incubation getting cold might have more of an effect than when they're a week in....

I've got some eggs under a broody I've never used before at the moment and every day I think I'm going to find her off them - so nervous! I also need to move her at some point before they hatch because she's not really in the best place for chicks, so I'm paranoid that she'll stop sitting when I do that too.
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Re: Sexlinked Breeding

Postby nhb » Thu Oct 29, 2015 3:55 pm

When they start to pip is supposed to be a good time so I've heard as they want to stay with the eggs then
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Re: Sexlinked Breeding

Postby Marina » Thu Oct 29, 2015 4:04 pm

I move once the chicks have hatched - and the hen has bonded to them - and not to the nest.

At pipping the eggs are very vulnerable to breaking and the hen does not hop off the nest as soon as a chick hatches. I have an old grate from a fridge which I put in front of the nest when pipping has started so she can't get out :mrgreen:
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