Chapter 13 RQ

2. Chapter 13 RQ • What are hereditary units of information called? • All chromosomes besides the X and Ys are known as _____________. • What keeps sister chromatids together until anaphase? • What is the purpose of meiosis? • What is the term for a fertilized egg?

3. 1. Explain why organisms only reproduce their own kind, and why offspring more closely resemble their parents than unrelated individuals of the same species. • It is a consequence of heredity, which results from the transmission of genes from parents to offspring • Because they share similar genes, offspring more closely resemble their parents or close relatives than others 

4. 2. Explain what makes heredity possible. • DNA is precisely replicated producing copies of genes that can be passed along from parents to offspring • Sperm and ova carrying each parents’ genes are combined in the nucleus of the fertilized egg 

5. Asexual Single parent  passes on all of its genes Offspring are genetically identical to parent Results in a clone Genetic differences may occur as a result of mutation (change in DNA) Sexual 2 parents  each parent passes on ½ of its genes Offspring have a unique combination of genes inherited from both parents Results in greater genetic variation – offspring vary genetically from their siblings & parents  3. Distinguish between asexual and sexual reproduction.

7. 4. Diagram the human life cycle and indicate where in the human body that mitosis and meiosis occur; which cells are the result of meiosis and mitosis; and which cells are haploid. • Mitosis  somatic cells, diploid (46 chromosomes); growth • Meiosis  gametes, haploid (23 chromosomes); sperm cells and ova 

10. 5. Distinguish among the life cycle patterns of animals, fungi, and plants. Animals • Gametes are the only haploid (n) cells • Meiosis halves the cells (2n  n + n) • Fertilization makes the 2n organism 

12. Fungi • Only diploid (2n) stage is the zygote • Resulting haploid (n) cells divide by mitosis to make the “n” organism • Gametes produced by mitosis 

13. Life cycles… Plants • Alternate generations • 2n stage – sporophyte (makes spores by meiosis) • Haploid spores divide mitotically to produce a multicellular haploid gametophyte (haploid gametes produced by mitosis) • Fertilization produces a diploid zygote – sporophyte 

14. 6. List the phases of meiosis I and meiosis II and describe the events characteristic of each phase. • Meiosis I  cell division that segregates the two chromosomes of each homologous pair and reduces the chromosome number by one-half; includes four phases: 1. Prophase I 2. Metaphase I 3. Anaphase I 4. Telophase I and Cytokinesis 

16. Meiosis I… • Prophase I  long and complex; 90% of time for meiosis - synapsis occurs (homologous chromosomes come together to form a tetrad; four chromatids) - crossing over occurs • Metaphase I  tetrads align at metaphase plate • Anaphase I  homologues separate and are moved toward the poles by the spindle apparatus • Telophase I & cytokinesis  the spindle apparatus continues to separate homologous chromosome pairs until the chromosomes reach the poles 

17. Meiosis II… • Meiosis II  this division separates sister chromatids of each chromosome; includes four phases: 1. Prophase II 2. Metaphase II 3. Anaphase II 4. Telophase II and Cytokinesis 

18. Meiosis II… • Prophase II  spindle apparatus forms and chromosomes move toward the metaphase II plate • Metaphase II  chromosomes align singly on the metaphase plate • Anaphase II  centromeres of sister chromatids separate, sister chromatids of each pair move towards opposite poles of the cell • Telophase II and cytokinesis  nuclei form at opposite poles of the cell - cytokinesis occurs producing four haploid daughter cells 

19. Synapsis  homologous chromosomes come together as pairs Crossing over can happen where the nonsister chromatids are linked  7. Describe the process of synapsis during prophase I, and explain how genetic recombination occurs.

20. 8. Describe key differences between mitosis and meiosis; explain how the end result of meiosis differs from that of mitosis. • Meiosis 1. Is a reduction division 2. Creates genetic variation 3. Is 2 successive nuclear divisions - produces gametes in animals • Mitosis - crossing over doesn’t occur - occurs in somatic cells (body cells) - copies the cells 

22. 9. Explain how independent assortment, crossing over, and random fertilization contribute to genetic variation in sexually reproducing organisms. • Independent assortment – orientation of the chromosome pairs is random at the poles (meiosis I) - each homologous pair orients independently of the others at metaphase I • Crossing over – exchange of genetic material between homologues (prophase I) - occurs when homologous portions of 2 nonsister chromatids trade places • Random fertilization – an egg is representative of 1 in 8 million possible chromosome combinations (same with sperm) - resulting zygote can have 1 in 64 trillion possible diploid combinations (not including crossovers) 

24. 10. Explain why inheritable variation was crucial to Darwin’s theory of evolution. • It is the basis for natural selection - variations selected that increase reproductive success - adaptation (the accumulation of heritable variations) 

25. 11. List the sources of genetic variation. • Sexual reproduction  independent assortment, crossing over, random gamete fusion • Mutation  random and rare structural changes made during DNA replication in a gene that could result from mistakes 