A karyotype is used to track the occurrence of a trait in a family

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Explanation:

A karyotype is the collection of all the chromosomes in an individual. Chromosomes can be isolated from cells and visualised by microscopy following the use of a stain to highlight the structural features of the chromosomes.

Karyotyping is used to assess structural or numerical aberrations in chromosomes that could cause genetic disease. For example is is often used to look for Down's syndrome, Turner's syndrome, or Cri du chat syndrome.

To track the occurrence of a trait in a family, a pedigree analysis is used. This is where the family tree is drawn out and individuals with a trait are marked in order to assess the prevalence of the trait in the family, and track it through generations.