During prophase I of meiosis, crossing over occurs between:

• A. Sister chromatids of the same chromosome
• B. Non-homologous chromosomes
• C. Centromeres of homologous chromosomes
• D. Non-sister chromatids of homologous chromosomes

Answer: (D)

Verified step by step guidance

1. Understand the context of prophase I in meiosis: Meiosis is a type of cell division that reduces the chromosome number by half, creating gametes. Prophase I is a key stage where homologous chromosomes pair up and exchange genetic material.
2. Define homologous chromosomes: These are pairs of chromosomes, one inherited from each parent, that have the same genes at the same loci but may have different alleles.
3. Clarify the concept of sister chromatids and non-sister chromatids: Sister chromatids are identical copies of a single chromosome, formed during DNA replication. Non-sister chromatids refer to chromatids from homologous chromosomes, which are not identical.
4. Explain crossing over: Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes. This process increases genetic diversity by creating new combinations of alleles.
5. Conclude why crossing over occurs between non-sister chromatids of homologous chromosomes: Non-sister chromatids are aligned closely during prophase I in a structure called a tetrad, allowing the exchange of genetic material at specific points called chiasmata.