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WHAT IS SEX-LINKED RECESSIVE

INHERITANCE IN BIRDS?

Sex-linked genes are located only on the sex-chromosomes. Sex-linked recessive means that the gene for a recessive factor in a bird is located on the sex- chromosome. Females have only one sex- chromosome (X-). Males have two sex- chromosomes (XX). In females, if they have the sex-linked gene, the factor will be visible, as they have only one sex-chromosome to which the sex-linked gene is on. In males, the sex-linked recessive factor will be visible if it is located on both sex-chromosomes. The factor is not visible in males if only one sex-chromosome carries the gene. If a male carries only one gene with the recessive factor, than it is split for the recessive factor. Females never can be split for a sex- linked gene. Here are some mating examples: X = Sex-Chromosome, also called X-Chromosome F = Factor (recessive)
MALE (XF)
F E M A L E
X
F
X
X
X
F
X
X
F
MALE (FF)
F E M A L E
F
X
X
X
F
F
F
F
F
MALE (XF)
F E M A L E
X
F
F
X
F
F
X
F
F
MALE (FF)
F E M A L E
F
F
F
F
F
F
F
F
F
Male: double-factor = visible for the recessive factor Female: without the recessive factor Results: 50 % males, single-factor = split for the recessive factor (XF) 50  % females, single-factor = visible for the recessive factor (F-)
Male: single-factor or split for the recessive factor Female: without the recessive factor Results:  25 % males, without the recessive factor (XX) 25 % males, single-factor = split for the recessive factor (XF)                       25 % females, single-factor = visible for the recessive factor (F-) 25 % females, without the recessive factor (X-)
Male: double-factor = visible for the recessive factor Female: single-factor = visible for the recessive factor Results:  50 % males, double-factor = visible for the recessive factor (FF) 50 % females, single-factor = visible for the recessive factor (F-)
(X-)
(F-)
(F-)
Male: single-factor or split for the recessive factor Female: single factor = visible for the recessive factor Results: 25 % males, single-factor or split for the recessive factor (XF) 25 % males, double-factor and visible for the recessive factor (FF)                       25 % females, without the recessive factor (X-) 25 % females, single-factor = visible for the recessive factor (F-)
(X-)
MALE (XX)
F E M A L E
X
X
F
F
F
X
X
X
X
Male: without the recessive factor Female: single factor = visible for the recessive factor Results:  50 % males, single-factor or split for the recessive factor (FX)                           50 % females, without the recessive factor (X-)                   
(F-)