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Sex-Linked Traits PDF Print E-mail

At first glance, sex-linked traits are more complex than autosomal traits. However, once you get the hang of them, they are actually easier to follow. Quaker mutations that are known to display sex-linked inheritance are the Pallid (Dark-Eyed Cinnamon) and the Cinnamon (Red-Eyed Cinnamon) traits. Though the only Lutino mutation identified to date is autosomal recessive, it is expected that a Lutino mutation will be identified as it has in many other species that manifests this inheritance. These two types of Lutinos are distinguished in other species by calling one "sex-linked Lutino" (SL Lutino) and the other "non-sex-linked Lutino". (NSL Lutino)

The difference between autosomal genes (traits) and sex-linked genes (traits) is that the former occur on the numerous pairs of autosomal chromosomes and the latter occur on the single pair of sex chromosomes.

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The reason why sex-linked genes (traits) are inherited differently is because, unlike autosomal chromosomes, the cock and the hen don't have similarly paired chromosomes. In fact, that is exactly what makes a cock a cock and a hen a hen. The cock has a pair of equal sized sex chromosomes which are designated with the letter "X".

Cock's Chromosomes
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However, the hen only has one copy of this "X" sex chromosome. Her other sex chromosome is much shorter and is termed the "Y" sex chromosome.

Hen's Chromosomes
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Any bird with a "XX" pair of sex chromosomes is a cock and any bird with a "XY" pair is a hen. If you think of gender as a "trait", we can use a Punnett square to determine the gender of offspring from any cock ("XX") and any hen. ("XY")
X x XY

X Y
X XX XY


The chicks are what we all know to be 50 % "XX" (cocks) and 50 % "XY". (hens) You can see that it is the hen that determines the sex of the offspring by contributing a "X" or a "Y" to the cock's constant "X" chromosome contribution. This is just the opposite in humans where the man determines the gender of children. Also notice that ALL hen offspring get their "X" chromosome from their father. (since they HAD to get their "Y" which makes them a hen from their mother) And, finally, note that ALL cock offspring ALWAYS receive their mother's only "X" chromosome. (because if he got the "Y", he would be a she) We will revisit these last two points later.


The cock's "XX" pair of sex chromosomes have normal pairs of genes as discussed in the previous sections. In the hen's XY pair, the genes on the lower half of the "X" chromosome are paired with the genes on the "Y" chromosome. However, there are no genes on the "Y" chromosome to pair with genes on the upper half of the "X" chromosome. So, genes (traits) that reside in the upper half of the "X" chromosome (above the pink line in the diagram below) are paired in cocks and remain as single genes in hens. These genes (above the pink line) are what are known as "sex-linked" genes. Those below the pink line will be ignored in this discussion.


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Sex-Linked Genetic Notation:

Genetic notation for sex-linked traits is a little confusing. The "X" and "Y" notations are used to allow the sex of the offspring to be identified. A superscript following a "X" indicates that letter as a sex-linked gene. (trait) We will use the superscript "P" for the normal green trait and "p" for the Pallid (Dark Eyed Cinnamon) trait. Thus, XP+ stands for the green trait at the sex-linked pallid site and Xp stands for the pallid trait at the sex-linked pallid site. The "Y" chromosome never has a superscript since sex-linked traits only occur above the pink line where the "Y" chromosome can't have a gene. "Y" is used alone to convey information about the sex of the bird and as a place keeper to remind us that there is no second gene for the hen at that site. Some examples of notation should clarify this. These are ALL the possible genetic combinations for the green and pallid traits.

XP+XP+
XpXp
XP+Xp
XP+Y
XpY
=
=
=
=
=
Green cock
Pallid cock
Green/Pallid cock
Green hen
Pallid hen


As you can see, all the birds with "XX" are cocks (regardless of the genes they carry) and all of the "XY" birds are hens. Also note that the pallid trait is recessive to the green trait since a "XP+Xp" bird is visual Green split for Pallid. And, finally, it's clear that a hen can NEVER be split for a sex-linked trait since she has only one copy of the gene. She is either Green or Pallid.

Single Gene Sex-Linked Inheritance:

Understanding how to describe Green and Pallid birds in notation allows us to use a Punnett square to predict some outcomes. Let's first practice with a Green x Green pair just to get familiar. Once again, the cock's possible contributions are tinted blue and the hen's possible contributions are tinted pink.
XP+XP+ x XP+Y

XP+ Y
XP+ XP+XP+ XP+Y

50 % of the offspring are Green cocks
50 % of the offspring are Green hens


You can see that the addition of the superscripts has not changed the way the "X" and "Y" chromosomes fall out. They are just as in the example above giving 50% cocks and 50% hens. In this case, all the associated genes are green, so all the offspring are too. Now, let's try a Pallid cock x Green hen.
XpXp x XP+Y

XP Y
XP XP+Xp XpY

50 % of the offspring are Green/Pallid cocks
50 % of the offspring are Pallid hens


Three things become apparent now. First and foremost, the color results of cocks and hens is different with sex-linked traits. With autosomal traits, no mention of gender was made because whatever colors resulted, they would be evenly divided between cocks and hens. Now that the sex chromosome is involved, though, things are different.


Second, you can see clearly now that it is the cock that determines whether the hen offspring inherit a sex-linked (pallid) trait.


And, third, all you would need to do with this pair is to look at the visual color of the chicks, and you would know, FOR SURE, their sex. All Green chicks are cocks which are split for Pallid and all Pallid chicks are hens. Let's reverse this cross with a Green cock and a Pallid hen.

XP+XP+ x XpY

XP Y
XP+ XP+Xp XP+Y

50 % of the offspring are Green/Pallid cocks
50 % of the offspring are Green hens


Once again, the color of the offspring is dependent on their gender (cocks are genetically different than hens) and the cock has determined whether the hen offspring are Pallid or not. It is also clear that the cock offspring inherit one of their father's "X" genes and MUST inherit their mother's only "X" gene. So, the make-up of cock offspring depends on input from BOTH parents contrary to that of hen offspring which only depends on input from their father. Our final example will be a Green/Pallid cock x Green hen.

XP+Xp x XP+Y

XP+ Y
XP+ XP+XP+ XP+Y
Xp XP+Xp XpY

25 % of the offspring are Green cocks
25 % of the offspring are Green/Pallid cocks
25 % of the offspring are Green hens
25 % of the offspring are Pallid hens


Once you get used to the superscripts, sex-linked traits are no more difficult to predict than autosomal. In this example, the genetics of all the hens will be known by just their visual color. (Green ones are XP+Y and Pallid ones are XpY) However, all the cocks will be "possibles" as they are all Green but half are XP+XP+ and half are XP+Xp.


All of the pairings and offspring for crosses involving only green and pallid traits can be viewed at the Pallid Tables page.

Combined Autosomal and Sex-Linked Trait Inheritance:


This is the most difficult 2 gene inheritance pattern to master. (and the most involved we'll deal with in these pages) However, once familiar with sex-linked inheritance, combining a sex-linked trait with an autosomal trait to predict their combined inheritance is relatively simple. It is no different in theory and practice than the last section of the Autosomal Traits page (Multiple Gene Inheritance) in which the combined blue and yellow sites were discussed. The only difference is that a sex-linked trait (with it's superscript) is substituted for one of the autosomal traits. We will examine the combined inheritance of the autosomal blue trait and the sex-linked pallid trait. The notation expressions for the possible parents are below.

B+B+
XP+XP+
= Green cock B+B+
XP+Y
= Green hen
B+b
XP+XP+
= Green/Blue cock B+b
XP+Y
= Green/Blue hen
b b
XP+XP+
= Blue cock b b
XP+Y
= Blue hen
B+B+
XP+Xp
= Green/Pallid cock

B+B+
XpXp
= Pallid cock B+B+
XpY
= Pallid hen
B+b
XP+Xp
= Green/Blue/Pallid cock

b b
XP+Xp
= Blue/Pallid cock

B+b
XpXp
= Pallid/Blue cock B+b
XpY
= Pallid/Blue hen
b b
XpXp
= Pallid Blue cock b b
XpY
= Pallid Blue hen



Note that there are 9 possible cock gene combinations and only 6 possible hen combinations. This is because hens cannot be split for the sex-linked pallid trait and, thus, cannot be Green/Pallid, Green/Blue/Pallid or Blue/Pallid. We will start with a normal Green x Green pairing to introduce the combined notation.

B+B+
XP+XP+
x B+B+
XP+Y
= Green cock cross Green hen


The cock can only contribute a B+ gene at the blue site (top) and a XP+ gene at the sex-linked pallid site. (bottom) Therefore, the ONLY combination he can give is this.

B+
XP+


Similarly, the hen can only give a B+ gene at the blue site. But, at the sex-linked pallid site, she can either pass on her XP+ gene to a cock chick or the "geneless" Y chromosome (as a place keeper) to a hen chick.

B+
XP+
or B+
Y


Filling these into a Punnett square, we would get the following:

B+B+
XP+XP+
x B+B+
XP+Y

B+
XP+
B+
Y
B+
XP+
B+B+
XP+XP+
B+B+
XP+Y

50 % of the offspring are Green cocks
50 % of the offspring are Green hens


Another way to represent offspring is in a table form. Such a table is below with the offspring of this cross entered. The visual color of the chicks are the columns and the split characteristics are entered in the boxes.

Offspring Green Blue Pallid Pallid Blue
Cocks US


Hens US




KEY: US = unsplit, SB = split Blue, SC = split Pallid, DS = double split = split Blue and split Pallid

Just as when we were dealing with the blue and yellow sites together, the blue and pallid pairs of genes are worked through the table "independently" of each other once the possible contributions by the cock and the hen are placed along the left and across the top of the table. A more involved example is that of a Blue cock x Pallid hen.

b b
XP+XP+
x B+B+
XpY
= Blue cock cross Pallid hen


The cock can only contribute a b gene at the blue site and a XP+ gene at the pallid site.

b
XP+


The hen can only give a B+ gene at the blue site, but can provide either an Xp or a Y at the pallid site.
B+
Xp
or B+
Y

The resulting Punnett square looks like this.
b b
XP+XP+
x B+B+
XpY

B+
Xp
B+
Y
b
XP+
B+b
XP+Xp
B+b
XP+Y

Results:
Offspring Green Blue Pallid Pallid Blue
Cocks DS


Hens SB



KEY: US = unsplit, SB = split Blue, SC = split Pallid, DS = double split = split Blue and split Pallid
50 % of the offspring are Green/Blue/Pallid cocks
50 % of the offspring are Green/Blue hens

Though all chicks are Green, their genetics are known for certain once they are sexed. Note again that all cock chicks inherit their mother's single sex-linked gene and that the single sex-linked gene of all hen chicks comes from their father. The results of the opposite pairing, Pallid cock x Blue hen, is below.
B+B+
XpXp
x b b
XP+Y
= Pallid cock cross Blue hen

The cock must contribute a B+ gene at the blue site and a Xp gene at the pallid site.
B+
Xp

The hen can only give a b gene at the blue site, but can provide either an XP+ or a Y at the pallid site.
b
XP+
or b
Y

Thus, the Punnett square looks similar, but gives different offspring.
B+B+
XpXp
x b b
XP+Y


b
XP+
b
Y
B+
XP
B+b
XP+Xp
B+b
XpY

Results:
Offspring Green Blue Pallid Pallid Blue
Cocks DS


Hens

SB

KEY: US = unsplit, SB = split Blue, SC = split Pallid, DS = double split = split Blue and split Pallid
50 % of the offspring are Green/Blue/Pallid cocks
50 % of the offspring are Pallid/Blue hens

The cock offspring are the same as in the previous example. However, the hen offspring are Pallid/Blue instead of Green/Blue even though one parent is Blue and one parent is Pallid in both cases. This is because (in this example) the father has the sex-linked pallid mutation instead of the mother and, thus, he gives it to all his hen offspring. For this reason, cocks with visual sex-linked traits (which have two copies) are considered more valuable than visual hens (which have only one copy) and are generally priced higher.

This example shows the power of knowing your genetics. All one would have to do is look in the nest box and one would know, FOR SURE, that all Pallid chicks were Pallid/Blue hens and all Green chicks were Green/Blue/Pallid cocks. A Green/Blue x Pallid pairing yields a slightly more complex result.
B+b
XP+XP+
x B+B+
XpY
= Green/Blue cock cross Pallid hen

The cock can contribute either a B+ or b gene at the blue site, but always gives a XP+ gene at the pallid site.
B+
XP+
or b
XP+

The hen can only give a B+ gene at the blue site, but can provide either an Xp or a Y at the pallid site.
B+
Xp
or B+
Y

The Punnett square is slightly larger, but still relatively straightforward.
B+b
XP+XP+
x B+B+
XpY


B+
Xp
B+
Y
B+
XP+
B+B+
XP+Xp
B+B+
XP+Y
b
XP+
B+b
XP+Xp
B+b
XP+Y

Results:
Offspring Green Blue Pallid Pallid Blue
Cocks SC, DS


Hens US, SB



KEY: US = unsplit, SB = split Blue, SC = split Pallid, DS = double split = split Blue and split Pallid
25 % of the offspring are Green/Pallid cocks
25 % of the offspring are Green/Blue/Pallid cocks
25 % of the offspring are Green hens
25 % of the offspring are Green/Blue hens

All offspring are Green and even after sexing, none of the genetics are known for sure. All are "possibles". The results of the opposite pairing, Pallid cock x Green/Blue hen, gives a similarly complex table full of "possible" offspring.
B+B+
XpXp
x B+b
XP+Y
= Pallid cock cross Green/Blue hen

The cock can only contribute a B+ gene at the blue site and an Xp gene at the pallid site.
B+
Xp


The hen can either give a B+ or b gene at the blue site and either an XP+ or a Y at the pallid site. Her possible contributions are below.
B+
XP+
or b
XP+
or B+
Y
or b
Y

The Punnett square is 1x4 instead of 2x2, but is still relatively straightforward.
B+B+
XpXp
x B+b
XP+Y

B+
XP+
b
XP+
B+
Y
b
Y
B+
Xp
B+B+
XP+Xp
B+b
XP+Xp
B+B+
XpY
B+b
XpY

Results:
Offspring Green Blue Pallid Pallid Blue
Cocks SC, DS


Hens

US, SB

KEY: US = unsplit, SB = split Blue, SC = split Pallid, DS = double split = split Blue and split Pallid
25 % of the offspring are Green/Pallid cocks
25 % of the offspring are Green/Blue/Pallid cocks
25 % of the offspring are Pallid hens
25 % of the offspring are Pallid/Blue hens


The cock chicks are the same as in the previous example, but the hen offspring are all visually Pallid. However, 100% of the chicks are still "possibles". Therefore, it would be advantageous to avoid such a cross unless necessary. As the degree of "splitness" increases, the complexity of the table increases such as a Green/Blue x Pallid/Blue pairing.

B+b
XP+XP+
x B+b
XpY
= Green/Blue cock cross Pallid/Blue hen


The cock can either contribute a B+ or b gene at the blue site, but can only give an XP+ gene at the pallid site.

B+
XP+
or b
XP+


The hen can either give a B+ or b gene at the blue site and either an Xp or a Y at the pallid site.

B+
XP
or b
XP
or B+
Y
or b
Y


The Punnett square is now a larger 2x4 matrix.

B+b
XP+XP+
x B+b
XpY



B+
Xp
b
Xp
B+
Y
b
Y
B+
XP+
B+B+
XP+Xp
B+b
XP+Xp
B+B+
XP+Y
B+b
XP+Y
b
XP+
B+b
XP+Xp
b b
XP+Xp
B+b
XP+Y
b b
XP+Y


Results:

Offspring Green Blue Pallid Pallid Blue
Cocks SC, DS, DS SC

Hens US, SB, SB US



KEY: US = unsplit, SB = split Blue, SC = split Pallid, DS = double split = split Blue and split Pallid

With this pairing, there are 8 possible offspring. (2x4 table) Even if there are duplicates, they are all brought down to the "offspring" table to preserve the genetic ratios of the various chicks. Thus, each box in the table represents 1/8th or 12.5 % of the whole. The results are as follows:

12.5 % of the offspring are Green/Pallid cocks
25.0 % of the offspring are Green/Blue/Pallid cocks
12.5 % of the offspring are Blue/Pallid cocks
12.5 % of the offspring are Green hens
25.0 % of the offspring are Green/Blue hens
12.5 % of the offspring are Blue hens


In this case, all the Green chicks are "possibles" and all the Blue chicks are "known". Sometimes the results allow a certain visual color of chick to always be "known" as in this case, and sometimes it is a particular gender which is always "known" such as in a Green/Blue/Pallid x Blue pairing.

B+b
XP+Xp
x b b
XP+Y
= Green/Blue/Pallid cock cross Blue hen


The cock can contribute either a B+ or b gene at the blue site and an XP+ or Xp gene at the pallid site.

B+
XP+
or b
XP+
or B+
XP
or b
XP


The hen can only contribute a b gene at the blue site and either an XP+ or a Y at the pallid site.
b
XP+
or b
Y


The Punnett square is now a 4x2 rather than a 2x4 matrix.

B+b
XP+XP+
x B+b
XpY



b
XP+
b
Y
B+
XP+
B+b
XP+XP+
B+b
XP+Y
b
XP+
b b
XP+XP+
b b
XP+Y
B+
Xp
B+b
XP+Xp
B+b
XpY
b
Xp
b b
XP+Xp
b b
XpY


Results:

Offspring Green Blue Pallid Pallid Blue
Cocks SB, DS US, SC

Hens SB US SB US


KEY: US = unsplit, SB = split Blue, SC = split Pallid, DS = double split = split Blue and split Pallid

12.5 % of the offspring are Green/Blue cocks
12.5 % of the offspring are Green/Blue/Pallid cocks
12.5 % of the offspring are Blue cocks
12.5 % of the offspring are Blue/Pallid cocks
12.5 % of the offspring are Green/Blue hens
12.5 % of the offspring are Blue hens
12.5 % of the offspring are Pallid/Blue hens
12.5 % of the offspring are Pallid Blue hens


All of the cocks are "possibles" and all of the hens are "known". Also, we see our first Pallid Blue chick. You may have noticed already that sex-linked (Pallid or Pallid Blue) hen chicks are easier to produce than cocks as they only require one copy of the gene to be visual compared to the cocks who need 2 copies for the trait to be visually expressed. Again, this explains why sex-linked cocks are more valuable and more expensive. One of the most complex of all tables to construct is a Green/Blue/Pallid x Pallid/Blue pairing.

B+b
XP+Xp
x B+b
XpY
= Green/Blue/Pallid cock
cross Pallid/Blue hen


The cock can contribute either a B+ or b gene at the blue site and an XP+ or Xp gene at the pallid site.

B+
XP+
or b
XP+
or B+
XP
or b
XP


Similarly, the hen can contribute either a B+ or b gene at the blue site and an Xp or a Y at the pallid site.

B+
XP
or b
XP
or B+
Y
or b
Y


The Punnett square is now a huge 4x4 matrix.

B+b
XP+Xp
x B+b
XpY



B+
Xp
b
Xp
B+
Y
b
Y
B+
XP+
B+B+
XP+Xp
B+b
XP+Xp
B+B+
XP+Y
B+b
XP+Y
b
XP+
B+b
XP+Xp
bb
XP+Xp
B+b
XP+Y
bb
XP+Y
B+
Xp
B+B+
XpXp
B+b
XpXp
B+B+
XpY
B+b
XpY
b
Xp
B+b
XpXp
b b
XpXp
B+b
XpY
b b
XpY


Results:

Offspring Green Blue Pallid Pallid Blue
Cocks SC, DS, DS SC US, SB, SB US
Hens US, SB, SB US US, SB, SB US


KEY: US = unsplit, SB = split Blue, SC = split Pallid, DS = double split = split Blue and split Pallid

Now we see that there are 16 possible offspring from this 4x4 (= 16) table. Each of these constitutes 6.25 % of the whole. The offspring are as follows:

6.25 % of the offspring are Green/Pallid cocks
12.5 % of the offspring are Green/Blue/Pallid cocks
6.25 % of the offspring are Blue/Pallid cocks
6.25 % of the offspring are Pallid cocks
12.5 % of the offspring are Pallid/Blue cocks
6.25 % of the offspring are Pallid Blue cocks
6.25 % of the offspring are Green hens
12.5 % of the offspring are Green/Blue hens
6.25 % of the offspring are Blue hens
6.25 % of the offspring are Pallid hens
12.5 % of the offspring are Pallid/Blue hens
6.25 % of the offspring are Pallid Blue hens


Though this cross will give the coveted Pallid Blue cock 6.25 % of the time, 75 % of the offspring are possibles and only 25 % are known. If one would instead choose a cock with a single extra blue gene (Blue/Pallid instead of Green/Blue/Pallid) to pair with the hen in this example, (Pallid/Blue) the resultant Punnett square is simpler and the offspring are MUCH more desirable and 100 % known!

b b
XP+Xp
x B+b
XpY
= Blue/Pallid cock
cross Pallid/Blue hen


The cock can only contribute a b gene at the blue site, but can give an XP+ or Xp gene at the pallid site.

b
XP+
or b
XP


The hen, however, can contribute either a B+ or b gene at the blue site and an Xp or a Y at the pallid site.

B+
XP
or b
XP
or B+
Y
or b
Y


The Punnett square is now a simpler 2x4 matrix.

b b
XP+Xp
x B+b
XPY



B+
XP
b
XP
B+
Y
b
Y
b
XP+
B+b
XP+Xp
b b
XP+Xp
B+b
XP+Y
b b
XP+Y
b
XP
B+b
XPXp
b b
XPXp
B+b
XPY
b b
XPY


Results:

Offspring Green Blue Pallid Pallid Blue
Cocks DS SC SB US
Hens SB US SB US


KEY: US = unsplit, SB = split Blue, SC = split Pallid, DS = double split = split Blue and split Pallid


12.5 % of the offspring are Green/Blue/Pallid cocks
12.5 % of the offspring are Blue/Pallid cocks
12.5 % of the offspring are Pallid/Blue cocks
12.5 % of the offspring are Pallid Blue cocks
12.5 % of the offspring are Green/Blue hens
12.5 % of the offspring are Blue hens
12.5 % of the offspring are Pallid/Blue hens
12.5 % of the offspring are Pallid Blue hens


A quick glance at the offspring table clearly shows that once the chicks are sexed, ALL the genetics of the chicks are known just by their visual color. In other words, there is only one entry in each box. This is a fantastic pairing that requires no test breeding of the offspring to determine genetics while producing a full 25 % Pallid Blue chicks; half of which are the rare and powerful Pallid Blue cocks! Pairings such as this are the goal of our breeding program.

All of the pairings and offspring for crosses involving the green, blue and pallid traits can be viewed at the Pallid Blue Tables page.

By now you should . . .


- understand what sex chromosomes and sex-linked genes/traits are.
- be familiar with which Quaker mutations are inherited as sex-linked.
- know whether sex-linked Quaker traits are dominant or recessive.
- understand why hens only have one copy of sex-linked genes while cocks have two copies.
- realize that a hen CAN NEVER be split for a sex-linked trait and why that is.
- be familiar with the "X" and "Y" notation of sex chromosomes and how to represent a cock and a hen with them.
- be comfortable with notation such as XP+Xp and XpY.
- be able to set up a Punnett square of a Green/Pallid x Pallid pairing and predict the genetics of their offspring. (try it !)
- be aware that cock and hen offspring of sex-linked crosses are necessarily of the same genetic make up or even color.
- know which parent is responsible for passing on a sex-linked trait to hen offspring.
- be comfortable with notation such as that below and be able to write out a description of each parent.

b b
XP+Xp
and B+b
XP+Y

- be able to plug information into a Punnett square to determine offspring for a pairing such as this. (try it !)

b b
XP+Xp
x B+b
XP+Y

- understand why a cock who is visual for a sex-linked trait is more valuable and powerful than a hen visual for the same trait.
- understand the value of producing genetically "known" offspring and use this knowledge along with genetics tables to set up more efficient parental pairs.

If these concepts are not clear at this point, you may want to review this page again before going on.

Had enough? Go back to our Home Page and surf some other stuff.

Still thirsty for more? Peruse the 54 possible parental pairings involving the green, blue and pallid traits on the Genetics Tables pages and view all their potential offspring.