1. Characteristic #4 All living things reproduce using the same genetic mechanism (code) Each organism reproduces its own species Offspring inherit genetic instructions from their parents through a molecule called DNA Offspring can differ from their parents (genetic variation)

2. Mitosis & Meiosis Making New Cells from Old Cells

3. Passing on Information  Genetics is the study of the transfer of information at the level of the cell. DNA stores genetic information DNA is divided into chromosomes Chromosomes come in homologous pairs Genes control traits Genes are on chromosomes

4. Chromosomes Chromosomes (DNA) are in the cell nucleus Humans have 23 pairs of chromosomes The number of chromosome pairs varies in each species

5. New Terminology Diploid: a cell with chromosome pairs. Human diploid cells have 23 pairs (46 chromosomes). Somatic Cells: body cells. All somatic cells are diploid

6. New Terminology Haploid: a cell that does not have pairs of chromosomes. Human haploid cells have 23 chromosomes. Gamete: sex cell (sperm, egg). All gametes are haploid.

8. Mitosis & the Cell Cycle Function: growth, repair, and replacement of cells. A diploid parent cell replicates its DNA, then splits in half. Both new daughter cells have a complete set of DNA Mitosis creates autosomes (body cells)

9. Three Stages of the Cell Cycle The cell cycle has 3 stages: Interphase: growth and replication Mitosis: the nucleus divides Cytokinesis: the cell divides The cell cycle has 3 stages: Interphase: growth and replication Mitosis: the nucleus divides Cytokinesis: the cell divides

10. Interphase The cell grows and the DNA replicates

11. Interphase At the beginning of interphase, the DNA is relaxed (chromatin). At the end, it tightens up (chromosomes)

12. Interphase After the chromosome (chromatid) makes a copy of itself, the new copy sticks to the old one to form an “X” shape (sister chromatids) Before Replication After Replication

13. Terminology Spindle fibers – strand-like fibers in the cell Centrioles – animal cell organelles that produce spindle fibers

14. Mitosis The cytoplasm of the cell divides, ending with a complete set of DNA on each side of the cell. Four steps: –Prophase –Metaphase –Anaphase –Telophase

15. Prophase Nucleus dissolves, spindle fibers stretch across the cell, centrioles move to poles

16. Metaphase The chromosomes line up on the cell equator, fibers attach to them from both sides

17. Anaphase The fibers shorten, splitting the chromosomes & pulling half of each pair to opposite poles

18. Telophase A new nucleus forms around each set of chromosomes, the cell starts to split in half

19. Cytokinesis the cell splits into two identical new daughter cells

20. Cytokinesis Animal cells: a cleavage furrow forms & the cell splits Plant cells: a cell plate grows across the center of the cell

22. Summary Mitosis is a way for cells to pass information to new somatic cells within the same organism The cell cycle & mitosis result in two diploid daughter cells that are identical to the original diploid parent cell Cell cycle and Mitosis are important in growth, replacement, and repair of all body cells

24. Meiosis

25. Homologous Chromosomes Chromosomes pair with the same genes

26. Humans have 23 pairs of homologous chromosomes

27. Sexual Reproduction Male sperm fertilizes the female egg DNA from 2 parents is combined To produce a baby with a normal # of chromosomes, each sperm and egg must have half the number of chromosomes

28. Gametes: Sex Cells Sperm and Eggs Found only in the testicles & ovaries Gametes are haploid: they have 23 chromosomes (no pairs) Formed through meiosis

29. Differences between gametes and body cells Gametes Autosomes Sex cells (sperm, eggs) Testicles and ovaries Haploid Made through meiosis No homologous pairs Body cells Everywhere else Diploid Made through mitosis Homologous pairs

30. Original diploid 4 haploid parent cell daughter cells Meiosis produces four different haploid daughter cells from one diploid parent cell

32. How does Meiosis Work? DNA replicates in the parent cell Homologous chromosomes swap genetic information by “Crossing over” The parent cell divides in half – each new cell now has one complete copy of DNA These 2 new cells divide again, splitting their copy of DNA in half 4 new haploid daughter cells have only ½ the DNA of the parent

33. A look at Meiosis

34. Crossing Over Homologous chromosomes move very close together… sometimes they swap pieces. This creates brand new combinations of genes on each chromosome Crossing over leads to genetic variation – the offspring has different traits than either parent

35. Comparing Mitosis and Meiosis Mitosis: diploid parent produces 2 identical diploid daughters Meiosis: diploid parent produces 4 unique haploid daughters

36. After Meiosis After Mitosis The 4 daughter cells will have half as many chromosomes as the parent. The 2 daughter cells will have the same number of chromosomes as the parent.

37. Meiosis vs. Mitosis If the parent cell has 60 chromosomes, how many will the daughter have after meiosis? Daughter cells produced by mitosis have 16 chromosomes. How many did the parent cell have? A sperm has 15 chromosomes. How many chromosomes did the parent cell have? If a daughter cell has 10 chromosomes and the parent had 20, was the daughter cell made through meiosis or mitosis?

39. Other Reproductive Issues Grab Bag of Knowledge Selective Breeding Asexual reproduction Alternation of generations Incomplete metamorphosis Complete metamorphosis

40. Selective Breeding

41. Dairy cows have been modified through selective breeding for large udders and high milk production. As a result, many cows have udders so large that they cannot walk without swinging their legs out to the side.

42. Asexual Reproduction Asexual reproduction is when one parent produces one or more identical offspring

43. Examples of Asexual Reproduction A branch of a tree grows into a new tree when planted Hydra create offspring that grow from their body and then pinch off

44. Sexual Reproduction Sexual reproduction involves the fertilization of an egg by a sperm (two parents). Offspring are different from the parents.

45. Animal Life Cycles: Metamorphosis Some organisms go through changes in form as they grow Insects undergo metamorphosis Incomplete metamorphosis has 3 stages: egg, nymph, adult Complete metamorphosis has 4 stages: egg, larvae, pupae, adult

46. Incomplete Metamorphosis Three stages: Egg Nymph: similar to adult but can’t reproduce Adult

47. Incomplete Metamorphosis in Grasshoppers Nymph Adult Eggs

48. Complete Metamorphosis Four stages: Egg Larvae (caterpillar) Pupae (cocoon) Adult

49. Butterfly Development Development of the crow butterfly: (Above left) egg; (Left) larvae; Above: pupae and cocoon; next slide: adult

51. Plant Life Cycles Alternation of Generations Plants alternate between a diploid and haploid phase. This is the alternation of generations.

52. What kind of reproduction is shown here?