Sexual Reproduction and Variation

1. Sexual Reproduction and Variation Set numbers of chromosomes are copied exactly and distributed during cell division.

2. Unit 7: Key Learnings • Simple cells divide through a process called binary fission. • Mitosis is a process that helps an organism grow in size or replenish lost or damaged tissue. • Meiosis produces the cells necessary for sexual reproduction.

3. Unit 7: Essential question How are the characteristics of mitosis and meiosis important to their roles in living organisms?

4. Launch activity: Growth and development sort Differentiation Cell Division Fertilization Courtship Development Genetic Recombination Growth Sex cell production

5. Unit 7: Concepts • Simple cell division (C) • Chromosome number (E) • The cell cycle (I) • Mitosis (E) • Meiosis and sexual reproduction (I) • Genetic disorders (C)

6. Essential question 1.1: How do simple cells divide? Dolly E. coli

7. I. New cells are constantly formed by cell division. • All organisms must copy their nucleic acids and divide their cytoplasm at some point in their life. • Unicellular organisms divide for reproduction • Multicellular organisms divide for growth and for reproduction in the formation of sex cells. • Each new cell should have exactly the same genetic information stored in it as its ancestors (good and bad is copied!).

8. Question: What types of problems could occur if the information stored in cells is copied incorrectly? • Cancer • Birth defects • Passage of genetic problems to offspring

9. II. Bacteria divide in a simple form of reproduction called Binary Fission. • A bacterium has a single circular chromosome. • This single chromosome is duplicated. • The cell pinches together and forms 2 new cells, each containing exactly the same genetic information. • This is much simpler than the division that eukaryotes, like humans, use.

11. Unit 7: Concepts • Simple cell division (C) • Chromosome number (E) • The cell cycle (I) • Mitosis (E) • Meiosis and sexual reproduction (I) • Genetic disorders (C)

12. Essential question 2.1: Why must sister chromatids be formed prior to division?

13. Activation: A fertilized egg must be copied and divided perfectly during development. zygote

14. I. Eukaryotic organisms often contain many cells (multicellularity). • About 2 trillion cells are produced by the human body every day to meet its needs (25 million /sec). • These cells have many chromosomes. • The chromosomes in a cell are direct copies of those that existed in the original fertilized egg (zygote). • These chromosomes need to be copied perfectly for development to occur normally.

15. II. A chromosome is a combination of DNA and several key proteins that help it to keep its shape. Chromosomes are... • stretched out very thin while being used. • broken up into thousands of different sections of information called genes. Eachgene is responsible for the production of one type of protein.

16. Chromosome Structure

17. III. Before division, each chromosome must be copied and condensed to facilitate movement. 1. The replication of a chromosome, results in two identical sister chromatids bound at a region called the centromere. • Each of the sister chromatids is ½ of the old DNA strand, and ½ newly formed nucleotides.

18. III.The copying of DNA is known as replication. • The two strands of DNA are pulled apart. • Nucleotides with the matching bases are attached to each open spot until the strand has been “replicated”.

19. VI. Production and separation of chromatids allows for cell division. • By pulling apart the replicated sister chromatids, a cell is able to generate two identical sets of chromosomes. • Each daughter cell will inherit a complete set of chromosomes.

20. Essential question 2.2: Why do sexually reproducing organisms have pairs of homologous chromosomes?

21. IV. Sexually reproducing organisms always have an even number of chromosomes. Pairs = X 2 2 x 2 = 4 3 x 2 = 6 13 x 2 = 26 ETC… • Each chromosome is part of a homologous pair, that are identical in size, shape and gene types (23 pairs = 46 total in humans). • Each of an organism’s parents contributed one member to the homologous pair. • Homologous pairs contain the same genes, but perhaps in different variations (e.g. blue eyes or brown eyes for the eye color gene)

22. Chromatids versus Homologues Resulting from fertilization Resulting from replication

23. Formation of homologous pairs and pairs of sister chromatids Dad’s sperm Mom’s egg Homologous pair + (Fertilization) = Zygote (fertilized egg) Sister chromatids Homologous pair Replication Homologous pairs of sister chromatids Cell division

24. IV./ 3. A karyotype shows each of an organism’s chromosomes aligned with its homologous partner. Sex Chromosomes of a male

25. Question:Why does the total number have to be even? • Even plus even equals even (22+22=44) • Odd plus odd equals even (23+23=46) • Even plus odd only happens as a result of a mutation (example: Down Syndrome).

26. Summarizer: With your partner, answers these questions: • What process leads to the presence of sister chromatids? • Why are they formed (discuss)? • What process leads to the presence of homologous chromosomes? • Why are they formed (discuss)?

27. Essential question 2.3: How are gametes different than somatic cells?

28. V. Some cells have half the normal number of chromosomes. • Normal body cells are called Somatic cells and sex cells (sperm and egg) are called Gametes. • “n” represents the number of chromosome types in an organism. • Somatic cells are called diploid (2n), since they always contain pairs of homologous chromosomes (23 pairs = 46). • Gametes are called haploid (n), since they always contain one of each type of chromosome (23 individual chromosomes). • Fertilization of a haploid (n) egg by a haploid (n) sperm yields a diploid (2n) Zygote(n + n = 2n).

29. VI. One of the pairs of chromosomes controls the gender of the individual. • The other pairs are called Autosomes, and play no part in gender determination (in humans- 22/23 pairs). • The Y chromosome holds all the genes that cause an embryo to become male. • Females have two X chromosomes (XX). • If an embryo has one Y chromosome, it becomes a male (XY). • Therefore, males always determine the sex of the offspring.

30. Gender determination occurs based on the sperm content. Dad (XY) Mom (XX) X X Y Girl (XX) Boy (XY)

31. 50 % 50 %

32. Summarizer: Complete the chromosome number review sheet.

33. Unit 7: Concepts • Simple cell division (C) • Chromosome number (E) • The cell cycle (I) • Mitosis (E) • Meiosis and sexual reproduction (I) • Genetic disorders (C)

34. Essential question 3.1: How is the cell cycle controlled?

35. I. The Cell Cycle describes the life of a Eukaryotic cell. • The Cell Cycle (5 stages) is a repeating sequence of growth and division. • A cell spends 90% of its life in the first 3 phases of the cell cycle (stages are collectively called Interphase). • The cell will only enter the second stage of the cycle if it is going to divide. • Eukaryotic cells must divide the contents of the nucleus as well as the contents of the cytoplasm. • Average time for this process is about 24 hours. Click the picture above to watch an overview of the cell cycle.

36. II. As checkpoints are met, signals are sent that prepare a cell to move forward.

37. III. During G1(Growth Phase 1) a cell grows rapidly and carries out normal cell functions. • G1 is when a cell does the things that it is made to do. • If the “G1restrictioncheckpoint” is met, the cell will proceed into the next stage of the cell cycle and prepare for division. (checkpoint to ensure DNA integrity and functionality) • Once division has yielded a complete organ, many cells stay in the G1 phase from that point forward and never divide again(G0) (e.g. muscle and nerve cells).

38. III. During S(Synthesis) phase a cell's DNA is copied. (replication) • This happens inside the nucleus. • Each of the chromosomes (46 total) are now attached to a sister chromatid (46 Xs).

39. IV. During G2 preparations are made for the nucleus to divide. • Check that all organelles have been duplicated. • Error check chromosomes. • A system of fibers called the spindle apparatus is built to move chromosomes around during the next phase. • The G2 checkpoint signals that the cell is ready to move into M phase.

40. V. During Mitosis the nucleus is divided into two nuclei (karyokinesis). • During this phase, the microtubules built during G2 divide the cells into two nuclei. • After this process concludes, the single cell has two complete nuclei, each containing exactly the same versions of all genes (clones).

41. VI. During animal cytokinesis the cytoplasm is divided into 2 complete cells, each containing their own nucleus.

42. Plant cell cytokinesis happens as a cell plate grows across the cell. Prior to cytokinesis After cytokinesis

43. Question: What’s the difference between karyokinesis and cytokinesis? • Karyokinesis is division of the nucleus (mitosis). • Cytokinesis is division of the cytoplasm.

44. VII. Environmental factors may cause mutations that disrupt the cell cycle, causing cancer. • Drugs, and alcohol • UV light from the sun • Viruses

46. Click the picture above to watch a video about cancerous cells. (2:37 – end)

47. Unit 7: Concepts • Simple cell division (C) • Chromosome number (E) • The cell cycle (I) • Mitosis (E) • Meiosis and sexual reproduction (I) • Genetic disorders (C)

48. Essential question 4.1: How does mitotic division produce two identical copies of the parent cell?

49. I. Mitosisoccurs in 4 very recognizable steps. Interphase (prior to Mitosis) • Prophase • Metaphase • Anaphase • Telophase • “IPMAT” helps you to remember the order of events: Interphase, Prophase, Metaphase, Anaphase, Telophase Mitosis Click here to watch an overview of mitosis. Beginning – 2:37

50. 1. Prophase