Questions: Chromosome breakage and abnormal re-attachment is one mechanism that causes the chromosomal structural change called a(n) trand - Another mechanism involves a crossover between nonhomologous chromosomes.

The answer is the first one: translocation.

Explanation:

1. Chromosome breakage and abnormal re-attachment is one mechanism that causes the chromosomal structural change called a translocation. This occurs when a segment of one chromosome breaks off and attaches to a different, nonhomologous chromosome.
2. Another mechanism involves a crossover between nonhomologous chromosomes, which can also result in a translocation. This type of crossover is abnormal because it typically occurs between homologous chromosomes during meiosis.

Summary: Chromosome breakage and abnormal re-attachment leading to a translocation is one mechanism of chromosomal structural change. Another mechanism involves crossover events between nonhomologous chromosomes, also resulting in translocations.