CHAPTER 8 The Cellular Basis of Reproduction and Inheritance

1. CHAPTER 8The Cellular Basis of Reproduction and Inheritance Modules 8.12 – 8.18

2. MEIOSIS AND CROSSING OVER 8.12 Chromosomes are matched in homologous pairs • _____ cells of each species contain a specific number of chromosomes • Human cells have 46, making up 23 pairs of ________ chromosomes Chromosomes Centromere Sister chromatids Figure 8.12

3. Karyotype______CellsHaploidCells

4. 8.13 Gametes have a single set of chromosomes • Cells with two sets of chromosomes are said to be ______ • Gametes are ______, with only one set of chromosomes

5. Repeated mitotic divisions lead to the development of a mature adult • The adult makes haploid gametes by _____ • All of these processes make up the _____ ___ cycle of organisms • At fertilization, a sperm fuses with an egg, forming a diploid ______

6. Haploid gametes (n = 23) Egg cell • The human life cycle Sperm cell MEIOSIS FERTILIZATION Diploidzygote (2n = 46) Multicellulardiploid adults (2n = 46) Mitosis anddevelopment Figure 8.13

7. 8.14 Meiosis reduces the chromosome number from diploid to haploid • Meiosis, like mitosis, is preceded by chromosome duplication • However, in meiosis the cell divides ____ to form _____ daughter cells

8. While they are paired, they ____ ___ and exchange genetic information • The homologous pairs are then separated, and two daughter cells are produced • In the first division, meiosis I, homologous chromosomes are _____

9. 9

10. MEIOSIS I: Homologous chromosomes separate INTERPHASE PROPHASE I METAPHASE I ANAPHASE I Centrosomes(withcentriolepairs) Microtubules attached tokinetochore Metaphaseplate Sister chromatidsremain attached Sites of crossing over Spindle Nuclearenvelope Sisterchromatids Tetrad Centromere(with kinetochore) Homologouschromosomes separate Chromatin Figure 8.14, part 1

11. The sister ______ of each chromosome separate • The result is four haploid daughter cells • Meiosis II is essentially the same as ______

12. MEIOSIS II: Sister chromatids separate TELOPHASE IAND CYTOKINESIS TELOPHASE IIAND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II Cleavagefurrow Sister chromatidsseparate Haploiddaughter cellsforming Figure 8.14, part 2

13. 8.15 Review: A comparison of mitosis and meiosis • For both processes, chromosomes replicate only once, during interphase

14. 8.16 Independent orientation of chromosomes in meiosis and random fertilization lead to varied offspring • Each chromosome of a homologous pair comes from a different parent • Each chromosome thus ____ at many points from the other member of the pair • Cross-Over (Does it happen) and where cross-over Occurs

15. The large number of possible _______ of chromosome pairs at metaphase I of meiosis leads to many different combinations of chromosomes in gametes • _____ fertilization also increases variation in offspring

16. POSSIBILITY 1 POSSIBILITY 2 Two equally probable arrangements of chromosomes at metaphase I Metaphase II Gametes Combination 1 Combination 2 Combination 3 Combination 4 Figure 8.16

17. Tetrad Chaisma Centromere Figure 8.18A