Time to Restore our Utility Poultry (T.R.O.U.P.) in the U.K.
Poultry Genetics
The problems and interesting facts about breeding poultry
  • Sex Linkage
    • 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).
      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.

    Silver Feathering
      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
    Feather sexing
      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
    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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