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Which of the two definitions of sex-linked trait is correct?

  • Traits controlled by genes present on the non-homologous region of sex chromosomes are called sex-linked traits.

  • Bodily traits controlled by genes present on the non-homologous regions of sex chromosomes are called sex-linked traits. Here by bodily traits I mean traits that are not involved with sex of an organism.

I read the first definition in the book Competition Science Visionand also from Instant notes genetics (page 163). The following is an excerpt from the latter

Sex linkage is not displayed by genes which map to a small segment of X chromosome, the pseudoautosomal region, the part of X chromosome that pairs with Y chromosome in meiosis.

The second definition is made up but sounds potentially intuitive to me.

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  • $\begingroup$ What do you mean by "traits that are not involved with sex"? Do you mean traits that are unrelated to (primary or secondary) sexual organs? $\endgroup$ – Remi.b May 27 '16 at 21:01
  • $\begingroup$ Yes that is what I meant $\endgroup$ – Tyto alba May 27 '16 at 21:03
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    $\begingroup$ I edited your post. Feel free to roll-back. If you agree that the format is much more pleasant to read than before then you can inspire yourself for future posts and try to always use a pleasant format for the readers. $\endgroup$ – Remi.b May 27 '16 at 21:19
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The first definition is correct.

A sex-linked trait is a trait affected by a locus on a sex chromosome.

If you google sex-linked trait, you will find this same definition (not the exact same words) over and over again.

The definition of sex-linked trait is NOT restricted to traits that are not unrelated to primary or secondary sexual organs. Any phenotypic trait can be sex-linked as long as the causal locus is on a sexual chromosome.

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  • $\begingroup$ "a locus that is present in individuals of only one sex..." isn't that wrong? Genes on the X are sex linked and therefore present in both sexes $\endgroup$ – rg255 May 27 '16 at 21:24
  • $\begingroup$ Yes, you are right that was wrong! I edited it. Thanks. $\endgroup$ – Remi.b May 27 '16 at 21:36
  • $\begingroup$ @Remi.b What are X-Y linked traits then? Are they what the book says, traits controlled by genes present on homologous regions of sex chromosomes? $\endgroup$ – Tyto alba May 27 '16 at 21:42
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    $\begingroup$ yes, traits causes by genes present on NON-homologous (you said the opposite in your comment) sequence on the X or Y chromosome. In case you did not know the non-homologuous sequence of X or Y chromosome. $\endgroup$ – Remi.b May 28 '16 at 7:21
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Sex linked traits are those controlled by genes on the sex chromosomes, regardless of whether or not they are related to reproduction. This can be the major (e.g. X or Z) or minor (e.g. Y or W) sex chromosomes.

"Sex linkage applies to genes that are located on the sex chromosomes. These genes are considered sex-linked because their expression and inheritance patterns differ between males and females." - link

Note. Most traits are polygenic thus some of the causal genes may be sex linked, and others on the autosomes. Phenotypic traits can therefore have varying degrees of sex linkage.

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