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    I was doing this question on inheritance:
    (Please tell me if the link doesn't work, I'll reupload) There isn't any further information given other than what's in this screenshot.

    Can anyone help me? Here is the mark scheme for this particular question, but I just don't understand it:

    (b) (i):

    3 and 4 produce unaffected male/8 / female/10, so must
    carry recessive;
    but both affected by nail-patella which must be dominant.


    3 inherits X from mother, who is not affected;
    if sex-linked, 3 would have nail-patella on X chr and
    would pass on to all female offspring;
    10 is recessive female, so gene not sex-linked.


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