Which of the following best describes what happens during a cross-over event? a. tetrads change orientation as they line up along the center of the cell. b. chromatids of homologous chromosomes exchange corresponding segments. c. x and y sex chromosomes overlap and combine together during metaphase. d. spindle fibers overlap and attach to the wrong chromosomes during anaphase.

Select all the correct answers. which statements fail to meet the requirements of a scientific claim? 1 even though evidence indicates that the solar system's planets follow elliptical paths, copernicus's model involving circular orbits is true. 2 the evidence supporting newton's laws of motion was accurate in newton's time, but the universe operates differently today. 3 flowers that reflect the most ultraviolet light are more likely to attract bees and other pollinators than flowers that reflect less ultraviolet light. 4 in the final 100 meters of a 10,000-meter race, an athlete's speed is more strongly related to anaerobic efficiency than to aerobic efficiency.

Which of the following is an oxidation-reduction reaction? (pictured below)

Describe two recent or ongoing space missions.