= Solution
Only <heterozygous> parents contribute an alternative-allele transmission contrast to the <transmission disequilibrium test>. Both parents are <homozygous> in rows 1, 13, 14 and 15, so \b[rows 1, 13, 14 and 15 are uninformative]. Their counts total 15 families. Every other row has at least one <heterozygous> parent. When both parents are <heterozygous> and the child is <heterozygous>, there is one transmission of each <allele>, regardless of the unresolved parent-specific phase; these transmissions contribute to both discordant cells.
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