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Sex-linked colours | Linkage between different loci | Mendel's Chart

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          The sex-linked phenotypes are cinnamon, slate, opaline, clearbody and ino. The X chromosome is responsible for carrying the genes for these colours. Cinnamon, slate and opaline, each have their respective locus while clearbody and ino share the same position on the X chromosome.

          The fact that hens are hemizygous, on other words, have one X chromosome and one Y chromosome while cocks have two X chromosomes has interesting consequences on the way sex-linked genes are passed on to the offspring. All the sex-linked colours named above are recessive mutations to their respective wild-type counterparts.

Symbols for sex-linked genes (according to Mutavi)

Type

Phenotype

 

 

 

cin +

Wild-type (dominant)

Normal

cin

Mutation (recessive)

Cinnamon

 

 

 

sl +

Wild-type (dominant)

Normal

sl

Mutation (recessive)

Slate

 

 

 

op +

Wild-type (dominant)

Normal

op

Mutation (recessive)

Opaline

 

 

 

ino +

Wild-type (dominant)

Normal

ino cb

Mutation (recessive)

Clearbody

ino

Mutation (recessive)

Ino

Table 11 – Symbols and visual effect of the individual genes carried by the X chromosome

          For each sex-linked colour a cock possesses two alleles, one on each X-chromosome. Because sex-linked colours are produced by the recessive mutations, a cock must be homozygous for a certain mutation to show the correspondent colour. If the cock has one copy the recessive mutation plus one copy of the dominant wild-type counterpart (heterozygous), it shows the normal colour. Heterozygous cocks are split for the recessive mutation that does not show on the phenotype.

          An hen cannot be heterozygous for any sex linked-colour. Hens have one X-chromosome, so they can only have one gene for each sex-linked colour. If a hen carries a recessive mutant gene she will show the correspondent colour, if on the other hand, she has the dominant wild-type gene she will show the normal colour.

          Table 12 shows some examples of genotypes and the correspondent phenotypes for the X chromosome. The symbols on the same line represent one genotype. On the left of each gene symbol is represented the X chromosome that carries it. The hen's Y chromosome is represented to show that it does not carry any of the genes in question.

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Home | Introduction | Notions on genetics | Two distinct loci and the colour pigments | Colour depth | The violet factor
Sex-linked colours | Linkage between different loci | Mendel's Chart
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