Regions of chromosomes where nonsister chromatids cross over are called __________.

• A. mutations
• B. homologs
• C. kinetochores
• D. tetrads
• E. chiasmata

Answer: (E)

Verified step by step guidance

1. Understand the context: During meiosis, homologous chromosomes pair up and exchange segments of genetic material. This process is known as crossing over.
2. Identify the key term: The regions where nonsister chromatids (chromatids from homologous chromosomes) physically exchange genetic material are crucial to this process.
3. Define the term: These regions are called 'chiasmata' (singular: chiasma). They are the visible manifestations of crossover events.
4. Differentiate from other terms: Mutations refer to changes in DNA sequence, homologs are pairs of chromosomes, kinetochores are protein structures on chromatids where spindle fibers attach, and tetrads are groups of four chromatids formed during meiosis.
5. Conclude with the correct term: Therefore, the regions where nonsister chromatids cross over are called chiasmata.