1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 2 major groups of Cells 1.Somatic Cells Body cells Diploid = 2n –two copies of each chromosome (1 from mom and 1 from dad) 2.Gametes –Sex cells –Haploid = 1n or n one copy of each chromosome –Ova or eggs in females (x) –Spermatozoa or sperm in males (x or y)

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 2 Types of Chromosomes in Cells Sex Chromosomes chromosomes that determine the gender of an organism Humans have 2 = X and Y Autosomes –All of the other chromosomes in an organism –Humans have 22 pairs

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Sex Chromosomes and Autosomes

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Meiosis Formation of gametes Division of 1 diploid cell into 4 haploid cells DNA is copied once but divided twice Two rounds of division = Meiosis I and Meiosis II Each round has 4 stages Prophase, Metaphase, Anaphase, Telophase Creates unique gene combinations

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Meiosis I prophase I, metaphase I, anaphase I, telophase I Crossing-over portions of homologous chromosomes exchange genetic material occurs during prophase I results in genetic “recombination” Genetic Linkage Genes located close together tend to be inherited together

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Stages of Meiosis I

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Meiosis II prophase II, metaphase II, anaphase II, telophase II Four new haploid cells result

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Stages of Meiosis II

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Comparing Meiosis and Mitosis

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Development of Gametes Spermatogenesis is the process by which sperm cells are produced 1 diploid cell produces 4 haploid sperm cells Oogenesis is the process that produces mature egg cells 1 diploid cell produces 1 haploid egg cell and 3 polar bodies that die off

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Meiosis in Male and Female Animals

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Sexual Reproduction the formation of offspring through meiosis and the union of a sperm and an egg Offspring produced by sexual reproduction are genetically different from the parents