Are there any examples of two "visible" or "obvious" phenotypic traits in humans that are a priori unrelated, but which tend to be inherited together (i.e. their inheritance probabilities are correlated) due to genetic linkage from their proximity on a chromosome?

I know that peas' flower color and grain shape are genetically linked, but are there any similar examples in humans?


Sex-linkage would be the canonical example.

In other words, people with phenotypically male or female sex characteristics have non-random genetic predilections towards specific X-linked traits such as hemophilia, color-blindness, Duchenne dystrophy, etc.

However, other classic examples would include linkage between blood group antigens and peptic ulcers.

For a general review of how linkage has been used historically in human genetic research see here.

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    $\begingroup$ The blood groups/peptic ulcers paper linked is from 1954 and behind a paywall. Given that peptic ulcers' cause wasn't sorted out for another 40 years or so and isn't a gene, I don't think it really fits the question here. $\endgroup$
    – Armand
    Sep 14 at 19:23
  • $\begingroup$ Sex linkage certainly counts, but I think there's a big difference from genetic linkage of genes on non-sex chromosomes. If I understand correctly, chromosomal crossover is fairly common between homologous chromosomes, so genes are faraway loci on the same chromosome are inherited fairly independently because there is a high probability of a chromosomal crossover occurring between those loci, so gene linking is the exception rather than the rule on non-sex chromosomes. But chromosomal crossover is much less common between and X and Y chromosomes because they aren't homologous (except at the .. $\endgroup$
    – tparker
    Sep 14 at 23:42
  • $\begingroup$ pseudoautosomonal regions). So if I understand correctly, gene linkage is more the rule than the exception for genes on the sex chromosomes, so it isn't as surprising, but it's more the exception off of the sex chromosomes. $\endgroup$
    – tparker
    Sep 14 at 23:44
  • $\begingroup$ @tparker The ballpark genetic length of human chromosomes is around 100 centiMorgans so very roughly two genes on a given autosome will have a fifty-fifty chance of being linked -- not so exceptional. $\endgroup$
    – Armand
    Sep 15 at 0:31
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    $\begingroup$ @MaximilianPress The pea phenotypes were in fact due directly to different but linked genes. Blood groups and peptic ulcer assocations seem plausibly to be due to the same gene, in which case genetic linkage would not be involved, but rather pleiotropy. $\endgroup$
    – Armand
    Sep 15 at 6:45

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