Question

which three statements best describe the events that occur after homologs synapse, early in meiosis i? select the three best answers.
recombination is an appropriate term because the chromosomes that result have a new combination of alleles--a mix of maternal and paternal.
crossing over and recombination are key aspect of mitosis.
crossing over is an appropriate term because the maternal and paternal physically cross each other (they look like an x under the microscope!).
after crossing over and recombination, sister chromatids are no longer identical--they each carry a unique combination of alleles.

Explanation:

• First statement: During meiosis I after synapsis, crossing - over occurs. This leads to recombination where chromosomes get a new combination of alleles (maternal and paternal), so this statement is correct.
• Second statement: Crossing - over and recombination are key aspects of meiosis, not mitosis. Mitosis is for growth and asexual reproduction and does not involve these processes in the same way as meiosis. So this statement is incorrect.
• Third statement: When homologs synapse, crossing - over occurs where maternal and paternal chromatids physically cross each other (and can look like an X - shaped structure called a chiasma under the microscope), so this statement is correct.
• Fourth statement: Before crossing - over, sister chromatids are identical (assuming no mutations). After crossing - over (a form of recombination), sister chromatids have a unique combination of alleles (since parts of maternal and paternal chromatids have been exchanged), so this statement is correct.

Answer:

• First statement: Recombination is an appropriate term because the chromosomes that result have a new combination of alleles - a mix of maternal and paternal.
• Third statement: Crossing over is an appropriate term because the maternal and paternal physically cross each other (they look like an X under the microscope!).
• Fourth statement: After crossing over and recombination, sister chromatids are no longer identical - they each carry a unique combination of alleles.