Crossing-over?

Crossing-over?

• A. Crossing-over produces new combinations of alleles and occurs during Prophase I
• B. Crossing-over is the separation of chromatids during Anaphase II
• C. Crossing-over is the duplication of a chromosome
• D. Crossing-over is the alignment of chromosomes at metaphase

Answer: (A)

Crossing-over is the genetic reshuffling that happens in meiosis when homologous chromosomes pair up. In prophase I, homologous chromosomes form a tetrad and nonsister chromatids exchange segments at sites called chiasmata. This swapping creates recombinant chromatids, so the resulting gametes carry new combinations of maternal and paternal alleles on the same chromosome, increasing genetic variation. Other descriptions don’t fit crossing-over: separating chromatids during anaphase II refers to the actual division of sister chromatids, not exchanging genetic material; duplicating a chromosome is DNA replication; aligning chromosomes at metaphase is about their arrangement before separation, not exchanging segments.

Crossing-over is the genetic reshuffling that happens in meiosis when homologous chromosomes pair up. In prophase I, homologous chromosomes form a tetrad and nonsister chromatids exchange segments at sites called chiasmata. This swapping creates recombinant chromatids, so the resulting gametes carry new combinations of maternal and paternal alleles on the same chromosome, increasing genetic variation.

Other descriptions don’t fit crossing-over: separating chromatids during anaphase II refers to the actual division of sister chromatids, not exchanging genetic material; duplicating a chromosome is DNA replication; aligning chromosomes at metaphase is about their arrangement before separation, not exchanging segments.