Sex linked vs autosomal traits

[sum1]

Is there a way in determining whether a trait is either sex-linked or autosomal by looking at a sample?

[alondouek]

What do you mean by sample? You can potentially identify sex linkage through sex bias in a population. Autosomal traits do not demonstrate significant sex bias.

[sum1]

As in if looking at a group of specie, how do I know if say eye colour was a sex linked trait or autosomal.

[alondouek]

Firstly, you wouldn't be able to make that comparison immediately across the species barrier. Some species have a different set of sex chromosomes to the human XY (I.e. birds have the WZ system).

But within a species, you'd look for familial sex bias and specific non-autosomal modes of transmission. Have you covered pedigrees yet? If not this will all make sense once you cover that area.

Also, you'd need to be careful with certain traits, as they may be under polygenic inheritance rather than simple autosomal/non-autosomal inheritance.

[SocialRhubarb]

It is often possible to disprove that the mode of inheritance is X-linked by examining specific cases.

For example, in humans, if the trait is recessive, but a female with the trait has a father without the trait, then the trait cannot be sex-linked.

Or if the trait is dominant, but a female without the trait has a father with the trait, then the trait cannot be sex-linked.

If there aren't any clear contradictions, then, like others have said, sex bias is probably the clearest method of determining mode of inheritance.

[Yacoubb]

It is often possible to disprove that the mode of inheritance is X-linked by examining specific cases.

For example, in humans, if the trait is recessive, but a female with the trait has a father without the trait, then the trait cannot be sex-linked.

Or if the trait is dominant, but a female without the trait has a father with the trait, then the trait cannot be sex-linked.

If there aren't any clear contradictions, then, like others have said, sex bias is probably the clearest method of determining mode of inheritance.

Wouldn't pedigree analysis be best. Typical MC question asking for which mode of inheritance is shown on a particular pedigree:
- Autosomal (dominant or recessive)
- X-linked (dominant or recessive)