1. Meiosis & Reproduction Chapter 7

2. objectives • Recognize that during meiosis, the formation of sex cells, chromosomes are reduced to half the number present in the parent cell • Explain how fertilization restores the diploid number of chromosomes • Recognize cells both increase in number and differentiate, becoming specialized in structure and function, during and after embryonic development • Identify factors (e.g. Biochemical, temperature) that may affect the differentiation of cells and the development of an organism • Distinguish between asexual (i.e. binary fission, budding, cloning) and sexual reproduction • Describe the advantages and disadvantages of asexual and sexual reproduction with regard to variation within a population

3. VI. Meiosis • Two divisions of the nucleus • Results in the formation of 4 gametes (egg, sperm) • Reduces the number of chromosomes by half (in humans from 46 to 23)

4. Stages of Meiosis I 1.*Prophase I- crossing over occurs, portions of one chromosome are broken and exchanged with portions of the other homologue **results in genetic variability

5. 2. Metaphase I- homologous chromosomes pair up together at the equator

6. 3. Anaphase I- spindle fibers shorten and homologous chromosomes separate and move toward opposite poles

7. 4. Telophase I and Cytokinesis

8. Meiosis II- same as mitosis 1. Prophase II 2. Metaphase II 3. Anaphase II 4. Telophase II & Cytokinesis

11. Females- meiosis is called oogenesis, forms 1 ovum and 3 polar bodies, occurs in ovaries

12. Males- meiosis is called spermatogenesis, forms 4 sperm cells, occurs in testes

13. Meiosis video

14. Sexual Reproduction- requires egg and sperm 1. Zygote- fertilized egg, first cell of new offspring

17. 2. Zygote divides by mitosis many times to produce a blastula (hollow ball of cells) Zygote 1 division 24 hours after conception Blastula 5 days after conception

18. Gastrula- one side of the blastula collapses and cells begin to change into 3 layers Gastrula Blastula

19. 4. The 3 gastrula cell layers begin to differentiate (change) into specific kinds of cells

21. Asexual Reproduction- does not require egg and sperm 3 Types: 1. Budding

22. 2. Regeneration

23. 3. Binary Fission

25. Advantages/Disadvantages Sexual reproduction- *provides genetic variability to the population Asexual reproduction- *produce many offspring in a short time *offspring have the exact same DNA as parent *all mutations in DNA get passed to offspring