Biology STAAR (State of Texas Assessments of Academic Readiness) Practice Test

What is nondisjunction?

1. The random assortment of chromosomes during meiosis

2. The failure of chromosomes to separate during meiosis

3. The correct division of chromosomes leading to equal gametes

4. The formation of homologous structures

The correct answer is: The failure of chromosomes to separate during meiosis

Nondisjunction refers to the failure of chromosomes to separate properly during meiosis, which can lead to gametes with an abnormal number of chromosomes. This process can occur during either the first or second meiotic division. When nondisjunction happens, it results in one gamete receiving an extra chromosome (trisomy) and the other gamete lacking that chromosome (monosomy). If these gametes participate in fertilization, the resulting zygote will have an abnormal chromosome number, which can lead to various genetic disorders, such as Down syndrome, Turner syndrome, or Klinefelter syndrome. The other options describe different biological processes. The random assortment of chromosomes during meiosis refers to the normal process of how chromosomes are distributed into gametes, which helps to create genetic diversity. The correct division of chromosomes leading to equal gametes is the desired outcome of meiosis, ensuring that each gamete has the correct haploid number of chromosomes. The formation of homologous structures pertains to evolutionary biology and describes how similar structures evolve in different species due to shared ancestry, rather than a process related to chromosome separation.