In many organisms, sex of the individual is determined genetically by the presence or absence of particular sex-chromosomes. For example: in humans, XX is female, XY is male; in chickens, ZW is female, ZZ is male (ie the male is homogametic not the female).

Definitions:
autosomal trait :- a gene carried on a non-sex chromosome and present in two copies in both sexes.
sex-linked trait - a gene carried on the sex chromosome that is present in both sexes; one copy in one sex, two in the other. In mammals, this is the X chromosome (one copy in males, two in females).
In birds, this is the Z chromosome (one copy in females, two in males).

If you cross chickens with two different feather patterns – barred and nonbarred.
1. 1 st cross
(female)nonbarred x (male)barred -------- all barred
Therefore …….. nonbarred is recessive
2. Reciprocal cross
(female)barred x (male)nonbarred --------(female)nonbarred and (male)barred>

genotype : (female)Z B - W (barred) x (male)Z b - Z b (nonbarred) gives
1/2 :(female) Z b -W (nonbarred) and 1/2 : (male)Z B - Z b (barred)

For the mating, ZbW x ZBZB, the progeny genotypic ratio is :
1 ZBW : 1 ZBZb
ZbW is a nonbarred female (remember the female is heterogametic in birds)
ZBZb is a barred male
From this mating sexing chicks at birth is possible.

For the mating, ZBW x ZbZb, the progeny genotypic ratio is :
1 ZbW : 1 ZBZb
ZbW is a non-barred female (remember the female is heterogametic in birds)
ZBZb is a barred male
From this mating sexing chicks at birth is possible.

For the mating, ZBW x ZBZb, the progeny genotypic ratio is :
1 ZBW : 1 ZbW : 1 ZBZB : 1 ZBZb
ZBW is a barred female (remember the female is heterogametic in birds)
ZbW is a non-barred female
ZBZB is a barred male
ZBZb is a barred male
From this mating sexing chicks at birth is only partially possible in that one-half of the females can be separated at birth.

A gene for silver plumage color also is sex-linked in chickens and can be used in the same manner to identify male and female chicks

A gene influencing rate of growth of wing primary feathers is located on the X chromosome. The allele for slow growth of primary feathers is dominant to the allele for fast feather growth. When a fast feathering rooster is mated to a slow feathering hen, male chicks are slow feathering and female chicks are fast feathering.
The difference is readily apparent and allows large numbers of male and female chicks to be separated quickly with a minimum of labor. Breeders must maintain genetic uniformity for the pertinent alleles in their male and female parent lines, to take advantage of the opportunity to feather-sex chicks.

Sex-limited inheritance
a - Where trait exists in only on one of the two sexes can occur at single-locus level (long feathers in chickens)
example: feather length in chickens
females all have short feathers
in males, s+s+ and s+s = short feathers
ss = long feathers
click here to see a picture of the difference in feathering

b - more common at the multiple-gene level involving complex traits (e.g., egg laying)

Sex-limited inheritance
A. Expression of a phenotype is limited to one sex
B. Gene is NOT on a sex chromosome
C. Example – domestic fowl tail and neck plummage.
In the males, cock-feathering is more long and curved, while in the female, hen-feathering is more short and rounded.


Genotype	Phenotype	Phenotype
	in females	in males
HH	Hen-feathered	Hen-feathered
Hh	Hen-feathered	Hen-feathered
hh	Hen-feathered	Cock feathered

Colour sexing
S > s : silver > gold
Parents: SS Male x s- Female
F1 Progeny: Ss and S- offspring all silver
ss Male x S- Female
F1 Progeny: Ss silver males
s- gold females

Dwarf gene DW > dw :Normal size > dwarf
Parents: dw dw x DW-
F1 Progeny: DW dw Male and dw - Female
Application: normal sized Male x dwarf females
The dwarf gene has pleiotropic effects:
• 20% smaller body weights
• 20% less feed consumption
• less eggs

Another is exemplified by the black/white plumage colors in chickens (Miller 1985, 1991).

links :http://esg-www.mit.edu:8001/esgbio/mg/sexlinkage.html
http://www.janecky.com/runyen/bio554/lectnotes/chp3sex.pdf
sex-linked imperfect albinism in chickens
old book on identifiying chicks (PDF)
Silversides F.G., Crawford R.D., (1990): Genetic Aspects of a New Mutation (Sal-s) to Sex-Linked Imperfect Albinism in Chickens (artilce no link)
Somes R.G. Jr. (1984) : International Registry of Poultry Genetic Stocks University of Connecticut, Storrs (article no link)
Werret W.F., Candy A.J., King J.O.L., (1959) Semi-Albino: A Third Sex-Linked Allelomorph of Silver and Gold in the Fowl Nature Vol.184: p.p.480-482 (article no link)
Sex linkage

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