Part 1 Multiple Choice When vertebrate eggs are developing they go through the first meiotic division and then pause at metaphase of the second meiotic division until fer tilization occurs before completing the second mei otic division MPF a protein regulates the pause and continuation of meiosis after fertilization Analyze the graph and answer questions 18 20 MPF Levels During Melosis Fertilization First meiotic Second meiotic division division Metaphase arrest 18 MPF is at high levels A at the beginning of the first meiotic division and at the beginning of the second meiotic division B at the beginning of the first meiotic division and at metaphase of the second meiotic division C only at the beginning of the first meiotic division D only at metaphase of the second meiotic division 19 MPF also slows the beginning of the first meiotic division to allow the egg to grow Therefore at this time MPF levels are A unchanged B low C high D high and low 20 Which of the following statements best describes the relationship between MPF and the slowing of meiosis in the developing egg A When MPF is high meiosis progresses B MPF has no effect on slowing meiosis C MPF is necessary for mitosis D When MPF is high meiosis slows down Study the diagram and answer questions 21 23 Gastrula 5 hours after fertilization Ectoderm DOS 18 hours 20 hours after after fertilization fertilization Mesoderm Yolk cell A heart tail eyes head B heart tail fins head 21 The cell layer from which the heart of the zebra fish develops is the A endoderm C mesoderm B ectoderm D yolk sac 22 One day after fertilization the zebra fish has C no internal organs D two cell layers in a gastrula 23 Twenty hours after fertilization the heart is C four chambered D ectoderm 1000 A two chambered B not divided into two chambers 1 day old embryo Heart or heart primordia MAN CHLIES