I joined this site so I could learn more about sex linking chickens.
I'm surprised to see that nobody has a word to say about it, which (I guess) makes me the default teacher...
So here's a copy and paste on sex linking for dwarfism~
Dwarfism due to the sex-linked recessive gene dw. Comparative size of two full-sib roosters. Left: Normal sibling (genotype Dw/dw). Right: Dwarf sibling (genotype dw/dw).
Dwarfism in chickens is an inherited condition found in chickens consisting of a significant delayed growth, resulting in adult individuals with a distinctive small size in comparison with normal specimens of the same breed or population.
The affected birds show no signs of dwarfism in the first weeks of age.[1]Differences in size due to dwarfism appear slow and progressively along the growing stage. Poultry breeders begin to distinguish gradually dwarfs from normal birds by their shortest shanks and smallest body size.[2][3] Depending on the breed, most types of dwarfism in chickens begin to be recognized when the birds reach 8–10 weeks of age,[4][5]but classification is more precise when the chickens are five months old or more. At this point differences between normal and dwarf sibs is evident in all males and in 98% of the females.[1]Dwarfs chickens reach sexual maturity and reproduce normally.
Dwarfism in chickens has been found to be controlled by several simple genetic factors. Some types are autosomicwhile others are sex-linked, but when poultry breeders make reference to 'dwarf chickens' they usually refer implicitly to sex-linked recessive dwarfism due to the recessive gene dw, located on the Z chromosome.
As sex-linked dwarf broiler breeder hens can bring about normal sized broiler chickens, sex-linked recessive dwarfism found application in poultry industry since the last decades of the 20th century.
These hens require less food and less housing space. Their feed intake do not need to be restricted. They also have more tolerance to heat (see: Advantages...). So the use of sex-linked dwarf broiler female parent stocks helps to save costs and to improve animal welfare and economic efficiency in European broiler industry (see: Use of...). But in spite of the proven advantages of raising dwarf breeder hens, their use is not generalized in broiler industry.
Autosomal types of dwarfism
Sex-linked dwarfismEdit
In birds, female is the heterogametic sex, that is, it has one Z and one Wsexual chromosome (genotype ZW), while male (the homogametic sex) carries two Z chromosomes (genotype ZZ). Thus, reciprocal crosses between normal and dwarf specimens may give rather different results.
Sex-linked recessive dwarfism, dwEdit
Hutt studied in the 1940s a remarkable type of dwarfism caused by only one sex-linked recessive gene to which he assigned the symbol dw.[1]
This mutation reduces body weight in females by 26 to 32%, but the effect is still greater in homozygous males, by about 42-43%. Chicks are normal size.[12][13] This is the best studied type of dwarfism in chickens. Sex-linked dwarfism in meat type breeds are first recognized by the shortening of the shanks than by the lowering body weight in the rearing period[14]
There are no signs of sex-linked dwarfism in the first weeks of age. Some individuals can be identified as dwarfs at 8–10 weeks of age, but classification is more precise when the chickens are five months old or more. At this point differences between normal and dwarf sibs is evident in all males and in 98% of the females.[1] These dwarfs reach sexual maturity and reproduce normally.
Normal females are always of genotype Dw/-, while dwarf females are always of genotype dw/-, because female is the heterogametic sex having only one Zchromosome. That is, females carrying a sex-linked gene of dwarfism are always pure and exhibit the trait. On the other hand, normal males may be either homozygous Dw/Dw or heterozygous Dw/dw, but dwarf males are always homozygous dw/dw.
Double dose of dwarf gene causes the dwarfism to be much more evident in males than in females. The above picture illustrates the comparative size of two full-sib roosters born the same day: Left: Normal sibling of genotype Dw/dw. Right: Dwarf sibling of genotype dw/dw.
I'm surprised to see that nobody has a word to say about it, which (I guess) makes me the default teacher...
So here's a copy and paste on sex linking for dwarfism~
Dwarfism due to the sex-linked recessive gene dw. Comparative size of two full-sib roosters. Left: Normal sibling (genotype Dw/dw). Right: Dwarf sibling (genotype dw/dw).
Dwarfism in chickens is an inherited condition found in chickens consisting of a significant delayed growth, resulting in adult individuals with a distinctive small size in comparison with normal specimens of the same breed or population.
The affected birds show no signs of dwarfism in the first weeks of age.[1]Differences in size due to dwarfism appear slow and progressively along the growing stage. Poultry breeders begin to distinguish gradually dwarfs from normal birds by their shortest shanks and smallest body size.[2][3] Depending on the breed, most types of dwarfism in chickens begin to be recognized when the birds reach 8–10 weeks of age,[4][5]but classification is more precise when the chickens are five months old or more. At this point differences between normal and dwarf sibs is evident in all males and in 98% of the females.[1]Dwarfs chickens reach sexual maturity and reproduce normally.
Dwarfism in chickens has been found to be controlled by several simple genetic factors. Some types are autosomicwhile others are sex-linked, but when poultry breeders make reference to 'dwarf chickens' they usually refer implicitly to sex-linked recessive dwarfism due to the recessive gene dw, located on the Z chromosome.
As sex-linked dwarf broiler breeder hens can bring about normal sized broiler chickens, sex-linked recessive dwarfism found application in poultry industry since the last decades of the 20th century.
These hens require less food and less housing space. Their feed intake do not need to be restricted. They also have more tolerance to heat (see: Advantages...). So the use of sex-linked dwarf broiler female parent stocks helps to save costs and to improve animal welfare and economic efficiency in European broiler industry (see: Use of...). But in spite of the proven advantages of raising dwarf breeder hens, their use is not generalized in broiler industry.
Autosomal types of dwarfism
Sex-linked dwarfismEdit
In birds, female is the heterogametic sex, that is, it has one Z and one Wsexual chromosome (genotype ZW), while male (the homogametic sex) carries two Z chromosomes (genotype ZZ). Thus, reciprocal crosses between normal and dwarf specimens may give rather different results.
Sex-linked recessive dwarfism, dwEdit
Hutt studied in the 1940s a remarkable type of dwarfism caused by only one sex-linked recessive gene to which he assigned the symbol dw.[1]
This mutation reduces body weight in females by 26 to 32%, but the effect is still greater in homozygous males, by about 42-43%. Chicks are normal size.[12][13] This is the best studied type of dwarfism in chickens. Sex-linked dwarfism in meat type breeds are first recognized by the shortening of the shanks than by the lowering body weight in the rearing period[14]
There are no signs of sex-linked dwarfism in the first weeks of age. Some individuals can be identified as dwarfs at 8–10 weeks of age, but classification is more precise when the chickens are five months old or more. At this point differences between normal and dwarf sibs is evident in all males and in 98% of the females.[1] These dwarfs reach sexual maturity and reproduce normally.
Normal females are always of genotype Dw/-, while dwarf females are always of genotype dw/-, because female is the heterogametic sex having only one Zchromosome. That is, females carrying a sex-linked gene of dwarfism are always pure and exhibit the trait. On the other hand, normal males may be either homozygous Dw/Dw or heterozygous Dw/dw, but dwarf males are always homozygous dw/dw.
Double dose of dwarf gene causes the dwarfism to be much more evident in males than in females. The above picture illustrates the comparative size of two full-sib roosters born the same day: Left: Normal sibling of genotype Dw/dw. Right: Dwarf sibling of genotype dw/dw.
