A donkey and a horse are considered separate species. They can mate, making a animal called a mule, but mules are sterile and cannot mate.
Because their offspring can't make donkeys and horses are separated by
O gametic isolation.
O reduced hybrid viability.
O mechanical isolation.
O reduced hybrid fertility.

19. a cell is viewed under a microscope and is found to have two nuclear envelopes and spindles that appear to be breaking apart. which phase of mitosis is the cell most likely in? a. metaphase b. prophase c. telophase d. anaphase

Why has two different alleles for the same trait?

Which of the following best describes the expensive tissue hypothesis? brains require more energy, so the gut had to be reduced, and larger brains and tool use led to higher quality diets. increasing body size means that homo neanderthalensis had to include more fat in its diet. brains require more energy, so the gut had to be reduced as brains got bigger. brains require more fat, so the gastrointestinal viscera (gut) had to expand, and hands were needed to acquire more food.