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PostPosted: Sun Aug 30, 2009 12:39 pm 
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Champion Bird
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This idea is really the brain-child of another member (rollyard) who has helped address the need for beginners like me, to start somewhere they can get their feet wet - but not drown completely in the theory.

As a backyard breeder, you may think yourself a likely candidate for experimenting with colours and other features in chickens you desire. But it's not a simple matter to select the right chickens - or more accurately, the right genetics. So here is your opportunity to ask those genetics questions that have eluded your understanding.

In the interests of learning and understanding some of the answers given, you may wish to read some books on the theory of genetics before jumping in. This isn't a pre-requisite, but it would be helpful. There is a recent book written by one of our members (blackdotte) called, "Genetics of Chicken Colours", and I have provided a link for how to purchase an e-copy here. Alternatively, for a hardcover copy, PM blackdotte on this forum.

If you have other reading material on genetics that has helped you understand the theory, feel free to add a website link or just the title of the book and author.

Remember to be patient for answers after asking a question, as people with more knowledge about genetics are busy people too. It may also take a while to put the answer together, if it's broken down into more simple terms. Hopefully we can help each other gain more understanding in what exactly goes on behind the theory.

I will kick-off with the first question: "What are the first genes a beginner should start learning about, and what are they responsible for affecting?"

The second part of my question, is for those who need a visual image to attach the gene too. :D


Further reading from BYP:

Chicken down colour: MASTERCLASS!!!
Genetics and breeding of BLUE in poultry

A useful tool:

The Chicken Colour Calculator:

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PostPosted: Sun Aug 30, 2009 12:50 pm 
A) what a gene is.

B) what a chromosome is.

C) that there are 2 genes only at one time at each point (loci) affecting the out come. the different genes for this loci are called allels.

D) recessive and dominant.


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PostPosted: Sun Aug 30, 2009 12:55 pm 
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Might I just add that this thread is PERFECT for anything you don't understand - if you don't understand what a chromosome is and how it fits in, and no matter how many times you Google it you still just...don't...get...it, please ask! I am quite happy to answer all sorts of questions that you may deem too silly to ask.

For instance, you may not grasp the concept of 'dominance', or 'partial dominance'.
Or maybe want to know what happens on a cellular level - e.g. what DOES DNA do? What is DNA?
Or how might epistasis affect poultry? Are there any examples?

Like Eggs said, doesn't mean tht you don't read a book - but if you still don't get it, ask!


Oooh, ruff's asked some like that. Are they questions, ruff?

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PostPosted: Sun Aug 30, 2009 1:24 pm 
no they are not questions from me but i think they are the very basics a person should know/learn/understand if they are going to get into genetics or cross breeding chooks.

also the word 'split' is used in avairy bird circles...this term is a laymans term for recessive.

k


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PostPosted: Sun Aug 30, 2009 2:23 pm 
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Old Mother Goose
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ruff wrote:
also the word 'split' is used in avairy bird circles...this term is a laymans term for recessive.

k


Now I didn't know that! See this thread is really going to work.

Ok here goes...
1) All cells (with the occasional exception but don't worry about this) have a cell nucleus ( like a central data-base).
The nucleus controls all the activities and functions of the cell.
The information to do this is carried on chromosomes.

2) The chromosomes are made up mostly of DNA.
The chromosomes are in pairs and there is a set standard number of chromosomes for each species of plant and animal.

3) Genes are parts of DNA on the chromosome that give instructions to make particular proteins. Each gene has a specific locus -(think location) on the chromosome.

4) The proteins that the genes are coded (by DNA) to make may be the proteins responsible for blue or brown eye colour, straight or curly hair, to be right or left-handed etc.

5) Some genes are dominant over others.

6) Genes are passed on from both parents in sexual reproduction - half from the mother and half from the father.
A sperm and an egg each contain only half the number of chromosomes from each parent. Remember the chromosomes are in pairs, these pairs are split when sperm cells and eggs are made.

7) After the egg has been fertilised by the sperm, the two sets of chromosomes are paired up. This pairing gives the newly developing chick its own individual combination of genes.

8) Back to dominant genes over recessive genes. When the newly fertilised egg develops into an embryo, the chromosomes in it's cell start making the proteins it's coded to do by the DNA in the genes.
Some genes totally dominate over the other in the pair.
So with each chromosome pair there will two genes for a certain trait. They may be the same, they may be different. Remember one came from mum, the other from dad.
If the two genes are the same, eg two genes for a big nose, then the offspring will have a big nose.
If the two genes are different; eg mum had a big nose and dad had a small nose, then what the child has will show what gene was dominant. Hopefully the small nose :lol:
The recessive gene will be "dominated" by the dominant gene.

9) To make matters more complicated, not all genes are fully dominant. There is such a thing as partial dominance.
We can come back to this later.

10)Genetics were first discovered ( I think) by a monk called Mendel who studied the colours of sweet peas in the garden. He discovered that if you cross a red flower with a white flower you get pink flowers.
The genetics we study today are called Mendelian genetics after him. ( Just a bit of trivia).
This ( correct me if I'm wrong Blackdotte) is an example of incomplete dominance and also a good way to introduce the terms heterozygote and homozygote.

A heterozygote has 2 different genes , a homozygote has two genes the same for a particular trait.

Typically the genes are allocated a letter for a trait.
In this example lets call the gene "R"
The dominant gene is always a capital letter, the recesive gene is always a small letter.

So for the sweet peas, 'R' is for red and 'r' is for white.
So we would call the red flower RR - as it has 2 genes for red
we would call the white flower rr as it has 2 recessive genes making it white.
The pink flowers are a mixture of the 2 genes Rr - note the recessive gene is always written second.


Now if you cross your red and white sweet peas this is what happens....

RR x rr
(red) (white)

gives Rr Rr

The progeny (offspring) will all be pink.

Both parents are homozygotes, the progeny get one each of the genes and are heterozygotes.
In this case the dominance is incomplete so all the flowers are pink.
If the dominance was complete, all the progeny would be red.


Now if we crossed the progeny with each other - so two heterozygotes
Lets see what happens.

Rr x Rr
(pink) (pink)

RR Rr rR * rr
red pink pink white

* correctly should be written Rr but just written that way to show how it happened.

So with the heterozygous cross, we have 25% red, 50% pink and 25% white sweet peas.

Have I lost anyone yet?

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Last edited by stella on Sun Aug 30, 2009 2:35 pm, edited 1 time in total.

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PostPosted: Sun Aug 30, 2009 2:25 pm 
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Old Mother Goose
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Hmmm the computer squashed together all my Rr's etc - wasn't supposed to look like that.

I really need to be able to do diagrams.

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PostPosted: Sun Aug 30, 2009 2:54 pm 
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And anyone in the know who can elucidate info about Mallard-derived duck plumage genetics would be very welcome to contribute! :D


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PostPosted: Sun Aug 30, 2009 2:59 pm 
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Sex-linkage (As I understand it - open to correction if I'm wrong)

Sorry, I can't give poultry examples here its not my field of expertise.

Now remember we all have a standard number of chromosomes BUT there is one pair that is a bit different.

A female has two 'X' chromosomes, a male has an 'X' and a 'Y' chromosome.
Yes men are inherently deficient as they lack that little bit extra that turns the X into a Y. :lol:

I guess though that it gets made up for because it means that it is sperm that determines whether the offspring is male or female.

Because eggs and sperm only have half of the pairs of chromosomes in them, all eggs will have an 'X' but half sperm will be 'X' and half will be 'Y'.
When the sperm fertilises the egg, if it is 'X' then the offspring will be female (XX), if the sperm carries the 'Y' the progeny (offspring) will be male (XY).

The genes that are carried on the tail of the X chromosome which the Y chromosome doesn't have are the sex-linked genes.

Hmm, I need to be able to draw a picture again. - If anyone doesn't see what I mean plz let me know.
Draw an X then draw a Y and see that the Y is missing the right hand bottom tail that the X has.

Now for my example.

Many people will have heard that tortoiseshell cats are all female and that there aren't many female ginger cats.
This is because the black and orange colour genes are carried on that bottom right tail of the X chromosome that the Y chromosome doesn't have.

B is the dominant gene for black.
b is the recessive for ginger.

Females can be BB (black), Bb (tortoiseshell, ie black and ginger) or bb ginger. ( ah! another case of partial dominance)
The reason there aren't many ginger female cats is because bb is homozygous recessive. Most will be black or tortie.

Males can only be B (black) or b (ginger) as there is no pair from the Y chromosome.

There is an exception - don't read this if you don't want to be confused.
There is a condition ( I think its called Klinefelter's syndrome) where by a male can actually be XXY instead of XY.
It's very rare and does apparently happen in humans.
These XXY males are infertile.
In a cat it does mean that the male can be a tortoiseshell as there are 2 X chromosomes to get the black and ginger genes from.
There was such a cat in the paper about a year ago that turned up at the RSPCA.

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Last edited by stella on Sun Aug 30, 2009 3:10 pm, edited 1 time in total.

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PostPosted: Sun Aug 30, 2009 3:00 pm 
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Old Mother Goose
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cackles wrote:
And anyone in the know who can elucidate info about Mallard-derived duck plumage genetics would be very welcome to contribute! :D


Way over my head!!!
I think that sounds like it needs it's own thread :lol:

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PostPosted: Sun Aug 30, 2009 3:03 pm 
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Omg thankyou! :thanks: Ive got books, but I still need people to dumb it down for me :? (Way down :lol: ). It may just sink in yet with this thread! :D


Cheers,
Michelle

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PostPosted: Sun Aug 30, 2009 3:12 pm 
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That's good information to start with Stella. I hope I'm not doubling up on info here, but in the interests of wrapping my head around the subject matter, I'll try to answer ruff's initial question. They confused me at first - answering my question with a question, but it kinda made sense when I went through the process.

Please forgive me if anything I present isn't entirely accurate. Jump in for corrections where necessary.

A) what a gene is?

This was very interesting to read about because it wasn't a thing per se, but a measurent of something else - DNA - most people would've heard of this term before. So what is DNA? My research material says DNA (or deoxyribonucleic acid) is the carrier of hereditary information.

A gene is a unit of that heredity information. Does that make sense? Feel free to correct me if I've misinterpreted what my study material says.

B) what a chromosome is?

A chromosome carries the genes, and usually pairs - so in effect, the chromosome is the body of that hereditary information.

C) that there are 2 genes only at one time at each point (loci) affecting the out come. the different genes for this loci are called allels.

I didn't find any information on loci in my material (it's very basic) but it did say that physical traits are controlled by gene pairs called alleles.

I've seen the term "alleles" mentioned in discussions about genetics before - now I I think I understand what it means. It is the control mechinism by which genes are expressed? But while they come in pairs, they can also act independently - which leads me to your last question.

D) recessive and dominant

A dominant gene will mask a recessive one, but as the hereditary information is still carried within the gene - it can reappear in subsequent offspring - but only if the dominant gene is no longer present.

So in answering my question with a question ruff, I have learned that:

a) my head hurts,
b) ouch
c) mercy please, and
d) okay, that's better - I think I've made it though the first step. :lol:

How did I do?

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PostPosted: Sun Aug 30, 2009 3:17 pm 
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[quote="Eggs-actly"]

C) that there are 2 genes only at one time at each point (loci) affecting the out come. the different genes for this loci are called allels.

I didn't find any information on loci in my material (it's very basic) but it did say that physical traits are controlled by gene pairs called alleles.

[quote]

Loci is the plural of locus. It's from the Latin ( most scientific stuff is unfortunately).
It means location, as Ruff said "point" on the chromosome.
So if you see locus or loci, don't go loco - think location, location, location. :thumbs:

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PostPosted: Sun Aug 30, 2009 3:30 pm 
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Oh wow, Latin, that so makes sense now. Mendel was a monk - of course he would've used Latin!! :lol:

See I KNEW genetics was a whole other language.

You're a champ Stella.

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PostPosted: Sun Aug 30, 2009 3:35 pm 
TAKE NOTE!

birds do not have the same X and Y chromsomes as mammals.

in the case of chickens the male carries 2 of the same sex genes and the female only one. this is important to understand as this influences the sex linked genes. for example barring...the rooster can have 2 genes for barring and the female only ever one.

k


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PostPosted: Sun Aug 30, 2009 3:39 pm 
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ruff wrote:
TAKE NOTE!

birds do not have the same X and Y chromsomes as mammals.

in the case of chickens the male carries 2 of the same sex genes and the female only one. this is important to understand as this influences the sex linked genes. for example barring...the rooster can have 2 genes for barring and the female only ever one.

k


Ah I'd long forgotten that or just plain didn't know!! Thanks Ruff.
I guess that's why sex-linkage in birds seems to be much more complex. Same sort of principle but more complicated.

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