Understanding Cell Reproduction: The Essentials

1. Honors BiologyChapter 9 JUST THE FACTS!

2. Cell Reproduction = the process by which cells divide to create new cells = cell division

3. Why Most Cells Divide: • 1. Surface Area to Volume Ratio: • As cells grow their volume increases faster than their surface area. • This decreases the surface area to volume ratio. • So, diffusion and other forms of transport cannot happen fast enough to keep the cell alive.

4. What would the volume of a cell be if each side measured 4 cm?

5. Why Most Cells Divide: (cont.) • 2. DNA Overload: • Genetic information cannot be processed fast enough in a really large cell to keep the cell functioning. • Giant amebas have 2 nuclei with 2 sets of chromosomes to overcome this problem!

6. Cell Cycle = the orderly sequence of growth and division for a cell • Events of the Cell Cycle: • G1 Phase: Period of growth before DNA is duplicated • S Phase: DNA is replicated (duplicated)

7. Cell Cycle • Events of the Cell Cycle: (Cont.) • G2 Phase: More growth, and organelles and materials needed for cell division are made. • M Phase: Cell division • 2 Parts: • Nuclear Division (Mitosis) • Cytoplasm Division (Cytokinesis)

8. Cell Cycle

10. B. The Cell Cycle- Series of events that cells go through as they grow and divide 1. Consists of 4 phases (interphase= G1, S, and G2) a. M phase (mitosis)- division of cell nucleus and cytokinesis b. G1 phase (gap)-periods of growth and activity c. S phase (synthesis)- DNA synthesized (duplicated) d. G2 phase (gap)- period of growth and acitivity. Organelles produced.

11. Two Types of Nuclear Division

12. D. Cytokinesis- division of cytoplasm and organelles. Follows mitosis or meiosis (division of the nucleus) 1. Animal cells- cell membrane drawn inward until cytoplasm is pinched into two nearly equal parts 2. Plant cells- cell plate forms midway between divided nuclei. Gradually develops into separating membrane. Eventually cell wall begins to appear.

13. Asexual Reproduction • Single parent produces offspring • All offspring are genetically identical to one another and to parent

14. Chromosome = thin thread of DNA wrapped around histone proteins. • Structure:

15. Chromosome

16. A. Chromosomes- genetic information carried on chromosomes 1. Before cell division each chromosome is replicated (copied) 2. Each chromosome consists of two identical “sister” chromatids 3. Each pair of chromosomes attached to area called centromere

17. Chromosome Number • Chromosome number is expressed as either: • 1. Diploid = 2n = the number of chromosomes found in somatic cells, where n = the number of homologous pairs.

18. Chromosome Number (cont.) • Haploid Number = n = the number of chromosomes in a gamete of that organism. (Half the diploid number) • Examples: • Humans: n = 23 • Gorillas: n = 24 • Pea Plants: n = 7 • Why is it necessary for gametes to have half the chromosome number of somatic cells?

19. CHROMOSOMES • Homologous chromosomes = a matched set; each chromosome has a partner chromosome that looks just like it and contains genes for the same things.

20. Homologous Chromosomes Carry Different Alleles • Cell has two of each chromosome • One chromosome in each pair from mother, other from father • Paternal and maternal chromosomes carry different alleles (allele = different form of a gene, but for the same inherited trait. Ex. We have genes for eye color, but you could have an allele for brown eyes, or an allele for blue eyes.

21. Mitosis Details: Interphase • Usually longest part of the cycle • Cell increases in mass • Number of cytoplasmic components doubles • DNA is duplicated

22. Mitosis Details: Prophase Duplicated chromosomes begin to condense

23. Mitosis Details: Late Prophase • New microtubules are assembled • One centriole pair is moved toward opposite pole of spindle • Nuclear envelope starts to break up

24. Mitosis Details: Transition to Metaphase • Spindle forms • Spindle microtubules become attached to the two sister chromatids of each chromosome

25. Mitosis Details: Metaphase • All chromosomes are lined up at the spindle equator • Chromosomes are maximally condensed

26. Mitosis Details: Anaphase • Sister chromatids of each chromosome are pulled apart • Once separated, each chromatid is a chromosome

27. Telophase • Chromosomes de-condense • Two nuclear membranes form, one around each set of unduplicated chromosomes

28. Results of Mitosis • Two daughter nuclei • Each with same chromosome number as parent cell • Chromosomes in unduplicated form

29. Mitosis Details - Result • Mitosis is then followed by Cytokinesis. • Final Result: • 2 identical offspring cells that have the diploid chromosome number and the same genetic information as the original parent cell.

30. Mitosis Details (cont.) • Abnormalities: • Cancer: uncontrolled cell division

31. Meiosis Details Chapter 9

32. Sexual Reproduction • Involves • Meiosis • Gamete production • Fertilization • Produces genetic variation among offspring

33. Sexual Reproduction Shuffles Alleles • Through sexual reproduction, offspring inherit new combinations of alleles, which leads to variations in traits • This variation in traits is the basis for evolutionary change

34. Factors Contributing to Variation Among Offspring • Crossing over during prophase I • Random alignment of chromosomes at metaphase I • Random combination of gametes at fertilization

35. Gamete Formation • Gametes are sex cells (sperm, eggs) • Arise from germ cells ovaries anther ovary testes

36. Meiosis: Phases and Events • Two consecutive nuclear divisions • Meiosis I • Meiosis II • DNA is NOT duplicated between divisions • Four haploid nuclei are formed

38. Meiosis I Prophase I Metaphase I Anaphase I Telophase I Meiosis II Prophase II Metaphase II Anaphase II Telophase II Stages of Meiosis

39. Prophase I Metaphase I Anaphase I Telophase I Meiosis I - Stages

40. Prophase I • Each duplicated, condensed chromosome pairs with its homologue • Homologues swap segments = Crossing Over • Each chromosome becomes attached to microtubules of newly forming spindle

41. Crossing Over • Each chromosome becomes zippered to its homologue • All four chromatids are closely aligned = tetrad • Non-sister chromosomes exchange segments

42. Meiosis I Each homologue in the cell pairs with its partner, then the partners separate

45. Effect of Crossing Over • After crossing over, each chromosome contains both maternal and paternal segments • Creates new allele combinations in offspring

46. Metaphase I • Chromosomes are pushed and pulled into the middle of cell • Sister chromatids of one homologue orient toward one pole, and those of other homologue toward opposite pole • The spindle is now fully formed

47. Anaphase I • Homologous chromosomes segregate(separate) from each other • The sister chromatids of each chromosome remain attached

48. Telophase I & Cytokinesis • The chromosomes arrive at opposite poles • The cytoplasm divides • There are now two haploid cells • This completes Meiosis I

50. Prophase II Metaphase II Anaphase II Telophase II Meiosis II - Stages