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Heredity of the Dunn-factor By Hennie Pienaar INTRODUCTION The easiest way of describing the heredity of the Dunn-factor is through making use of the Punnette squares. The Punnette square works as follow: Take for example a chequer cock (♂) with the genetic combination of Cb (a nonpurebred chequer (C) with the blue factor (b) which is recessive) and a blue bar hen (♀) with the genetic combination of bb (purebred blue factor). ♂ Square 1 (top left) represents the combination of the genetic factor C (Chequer) from the cock and the genetic factor b (Blue) of the hen. The result is Cb, a non-purebred chequer cock or hen. C b ♀ b Cb b ♂ C Square 2 (top right) represents the combination of the genetic factor b (Blue) from the cock and the genetic factor b (Blue) of the hen. The result is bb, a nonpurebred blue bar cock or hen. ♀ b b bb b ♂ Square 3 (bottom left) represents the combination of the genetic factor C (Chequer) from the cock and the genetic factor b (Blue) of the hen. The result is Cb, a non-purebred chequer cock or hen. C b ♀ b Cb b ♂ Square 4 (bottom right) represents the combination of the genetic factor b (Blue) from the cock and the genetic factor b (Blue) of the hen. The result is bb, a purebred blue bar cock or hen. C b b ♀ b bb ♂ We can summarize it as follow: C b b Cb bb b Cb bb 50% from the mating will be chequer cocks or hens with the blue factor recessive. 50% from this mating will be blue bar cocks or hens (purebred for the blue factor.) ♀ DUNN FACTOR : LINKED TO THE SEX CHROMOSONE The factor for the Dunn factor is found (like the factor for ash red) on the same chromosome as the sex factor. It is thus linked to the sex chromosome. The difference between the ash red factor and the dunn factor is that ash red is a dominant factor and the dunn is recessive. The Punnette Squares will help as to understand it better. Remember, a cock has two X chromosomes (XX), which not only determine the sex but also have a lot of other genetic information. A hen has only one X chromosome and a Y chromosome (XY). The latter is a vacant chromosome, which carries no hereditary (genetic) information. ♂ Figure 1: X X Xd XXd XXd Y XY XY A black factor cock (blue, chequer, penciled or dark) is paired with a Dunn hen, with the factor for Dunn linked to her X-chromosome. In the progeny: 50% will be blue bar or chequer cocks carrying the Dunn factor recessive. 50% will be blue bar, chequer, and etc. hens. ♀ Conclusion: All the male progeny won’t be dunns their selves, but they will carry the dunn factor. All the hens of this mating won’t either be dunns or carrying the Dunn factor. 0% of the progeny will be Dunns. ♂ Figure 2: X Xd X XX XdX Y XY XdY A blue bar, chequer, penciled or dark cock with the Dunn factor recessive is paired with a blue bar, chequer, etc. hen In the progeny: 25% are cocks and will be blue bar, chequer, etc, not carrying the Dunn factor. 25% are cocks and will carry the Dunn factor recessive. 25% are blue bar, chequer, and etc. hens. 25% will be Dunn hens. ♀ Conclusion: Halve of the male progeny won’t be dunns their selves, but they will carry the dunn factor. Halve of the male progeny won’t either be dunns their selves, or carry the dunn factor. Halve the hens of this mating won’t either be dunns or carrying the Dunn factor. Halve of the hens will be Dunns. 25% of the progeny will be Dunns ♂ Figure 3: X Xd Xd XXd XdXd Y XY XdY A blue bar, chequer, penciled or dark cock with the Dunn factor recessive is paired with a Dunn hen, with the factor for Dunn linked to her X-chromosome. In the progeny: 25% are cocks and will carry the Dunn factor recessive. 25% are cocks and will be purebred for the Dunn factor 25% are hens and will be blue bar, chequer, and etc. hens. 25% will be Dunn hens. ♀ Conclusion: Halve of the male progeny won’t be dunns their selves, but they will carry the dunn factor. Halve of the male progeny will be dunns. Halve the hens of this mating won’t either be dunns or carrying the Dunn factor. Halve of the hens will be Dunns. 50% of the progeny will be Dunns! ♂ Figure 3: Xd Xd Xd XdXd XdXd Y XdY XdY A Dunn cock is paired with a Dunn hen, with the factor for Dunn linked to her Xchromosome. In the progeny: 50% are cocks and purebred for the Dunn factor. 50% will be Dunn hens. ♀ Conclusion: All of the male progeny will be dunns. All of the hens will be Dunns. 100% of the progeny will be Dunns!