I have tried a to decide if this is a autosomal dominant, recessive or a mitochondrial disorder.

Is it possible to know for sure, or do you have to use probability?

(English is not my native language)

No other pedigrees have had carriers marked so I did not expect this one had it either.

Auto dominant.

I:1 aa I:2 A- II:1 aA II:2 aa II:3 aa II:4 aA II:1 children could have got a from him and a from her the the disorder would be gone. III:9 children got her dominant A

Recessive I:1 A- I:2 aa II:1 aa II:2 A- II:3 A- II:4 aa

Mitochondrial disorder I read "transmission only accours through females"

  • 1
    $\begingroup$ Could you please share your findings/rational so far on the matter and what makes you think it is autosomal or mitochondrial? This will show that you have thought about the question and will encourage others to contribute and point you to the right answer. $\endgroup$ Jun 16 '14 at 20:40
  • $\begingroup$ Since other pedigrees we have used have not had carriers marked I presumed this would not either. $\endgroup$
    – Fredrik
    Jun 16 '14 at 21:27

Mitochondrial because all the offsprings have the same trait as that of the female parent. Lets go through the possibilities one at a time. Assuming you have no carriers (you do not have any carrier symbols) we can work out the following.

Autosomal Recessive?

This might be the case if we assume the male in the first generation is a carrier.

Autosomal Dominant?

This might be the case but it is unlikely. Looking at the first generation possibly yes, as 50% of offspring have the trait. Looking at the second generation however only 3 out of 9 offspring have the trait. Making autosomal dominant unlikely (but it is still a possibility.)

In the test, if you have to go with one option, mitochondrial inheritance is the best because there are no assumptions at all but if multiple options may be correct, you can have any of them.

  • 2
    $\begingroup$ Actually, all offspring of females with the trait are affected ... $\endgroup$
    – Rory M
    Jun 16 '14 at 22:41
  • $\begingroup$ ah yes sorry my mistake, i read the female in the first generation as a daughter not a wife. so it is mitochondrial. Thanks $\endgroup$
    – Spinorial
    Jun 16 '14 at 22:52
  • $\begingroup$ As Rory has pointed out, there is no incomplete penetrance if we accept it as a mitochondrial trait. Besides that, your "Sex-linked?" point seems to be incorrect. In this case we can rule out the case of a dominant X-linked locus based on the observation that males didn't pass the trait to their daughters (decisive argument) and that sick heterozygous mothers transmitted the trait to all of their progeny (in statistical terms). $\endgroup$
    – alephreish
    Jun 17 '14 at 8:46
  • $\begingroup$ It cannot be X linked dominant. If it were then the male in the top left corner would always have daughters who had the trait as they need to inherit one X from their mother and the other trait X, X_T from there father. Resulting in XX_T and if X_T was dominant they would show the trait. $\endgroup$
    – Spinorial
    Jun 17 '14 at 10:21
  • $\begingroup$ Please read my comment again. Your argument was: it's not a sex-linked locus, "because both males and females are effected." $\endgroup$
    – alephreish
    Jun 19 '14 at 14:59

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