Question

"Crossing over" in eukaryotes most frequently occurs between a. two homologous chromosomes of a diploid germ-cell b. two sister chromatids of a diploid somatic cell c. homologous chromosomes from two different haploid germ cells immediately following fertilization d. randomly homologous regions of two nonhomologous chromosomes e. chromosomes of different cells during very early development (example 4 to 16 cell stage and metazoans)

Answer 1

Crossing over typically occurs between two homologous chromosomes of a diploid germ-cell during prophase I of meiosis, resulting in the exchange of genetic material and contributing to genetic diversity.

Step-by-step explanation:

Crossing over most frequently occurs between two homologous chromosomes of a diploid germ-cell during prophase I of meiosis. This process involves the exchange of genetic material between non-sister chromatids of homologous chromosomes. During prophase I, homologous chromosomes pair up, aligning gene-for-gene, and form a tetrad. A crossover event can occur, where material from two non-sister chromatids is exchanged, resulting in recombinant chromosomes with mixed genetic material from both parents.

This recombination contributes to the genetic diversity of gametes and, consequently, the potential variation in the offspring. Each crossover event shuffles the genes on the chromosomes, producing unique genetic combinations and aiding the natural variation observed within a species.

To answer the student's question, crossing over most frequently occurs between two homologous chromosomes of a diploid germ-cell (option a). This is when both chromosomes from a pair exchanged segments of DNA, leading to gametes that carry a mix of alleles from the individual's parents. This genetic shuffling is essential for ensuring the diversity of traits in subsequent generations.