3
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$\text{So... here is the given pedigree chart:}$

Ped1

My question is ... whether this is an autosomal or a X-linked recessive trait.


The book I was following gave me this info:

Ped2


My Attempt:

Looking at the chart ... it all comes down to either X-linked recessive or Autosomal recessive.

According to Rule 1. under these conditions:

  1. If it appears with equal frequency in both Males and Females -- Autosomal
  2. Otherwise , if more male than female -- X-linked

But my teacher said ... "its not always so"

So.... I tried with both once (brute force method ... going through all possibilities) and I could not understand which one...

It seems both are correct (which obviously is not possible)

So can anyone please help me with this problem!?

Thanks!

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  • $\begingroup$ Are squares males and circle females? $\endgroup$ – Remi.b Feb 20 '17 at 14:30
  • $\begingroup$ It is both possible that the trait is x-linked recessive and autosomal recessive. If autosomal recessive, that would require individual 12 to be heterozygous though. $\endgroup$ – Remi.b Feb 20 '17 at 14:34
  • $\begingroup$ @Remi.b Yes ... and the darkened ones are the affected ones $\endgroup$ – Abhinav Kochhar Feb 20 '17 at 14:35
  • $\begingroup$ The rule is you have to see 1st if the pedigree obeys Y-liked inheritance, if not then whether dominant/recessive. Once you figure out that (say it turned out to be recessive) see if it obeys X-linked or not. If it does the pedigree shows X-lined(recessive) trait. If it doesn't then it is autosomal and applying the genotypes you'll see there's no conflict and it obeys Autosomal inheritance for sure. The list of characters they are not always true for all pedigree charts, you'll find some matching while others may not. $\endgroup$ – Tyto alba Feb 20 '17 at 15:02
  • $\begingroup$ I would suggest you to consult your teacher because it is next to impossible to explain in a written Q&A format. Besides there are a number of ways this is taught, learning from more than one source will actually confuse you. $\endgroup$ – Tyto alba Feb 20 '17 at 15:08
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With the currently given information both autosomal and X-linked recessive is possible:

(WARNING extremely sloppy Paint editing ahead)

This is a possible scenario for an autosomal recessive trait: Autosomal gene inheritance

And this is one for a X-linked trait: X-linked gene inheritance

Ideally you would extend the chart until you encounter a scenario where an affected female has healthy male offspring (which indicates an autosomal trait).

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  • $\begingroup$ For both autosomal and X-linked recessive, we must make the assumption that 3 is heterozygous. The genotype of 1 shouldn't matter in either case, and is most likely homozygous. $\endgroup$ – canadianer Feb 20 '17 at 22:16
  • $\begingroup$ Oops you are absolutely right $\endgroup$ – Koen vd H Feb 21 '17 at 6:40
  • $\begingroup$ Thanks for your comment on my answer. You're absolutely right and, actually, the entire answer is now wrong. $\endgroup$ – canadianer Feb 21 '17 at 16:45
  • $\begingroup$ @canadianer I suppose X-linked might still be slightly more likely as autosomal assumes subject 12 to be a heterozygous outsider. $\endgroup$ – Koen vd H Feb 21 '17 at 21:22

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