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Chapter 13 - Meiosis and Sexual Life Cycles

Chapter 13 - Meiosis and Sexual Life Cycles . Review: Describe the functions of mitosis. High frequency quiz mistakes:. 1. Incorrect number of chromosomes used in depiction of mitotic cell division. Question stated that the cell was diploid and the haploid number (n) was 2. . Diploid (2n).

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Chapter 13 - Meiosis and Sexual Life Cycles

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  1. Chapter 13 - Meiosis and Sexual Life Cycles Review: Describe the functions of mitosis. High frequency quiz mistakes: 1. Incorrect number of chromosomes used in depiction of mitotic cell division. Question stated that the cell was diploid and the haploid number (n) was 2. Diploid (2n) Haploid number (n) (number of chromosomes in a set) 2 sets X 2 = 4 chromosomes in the cell

  2. Chapter 13 - Meiosis and Sexual Life Cycles Review: Describe the functions of mitosis. High frequency quiz mistakes: Practice A. How many chromosomes in a triploid cell with a haploid number of 7? 21 B. A diploid cell has 24 chromosomes. What is the value of n? 12 C. A 4n cell has 40 chromosomes. What is the ploidy of this cell and how many chromosomes would you expect to find in its gametes? Tetraploid, 20

  3. Chapter 13 - Meiosis and Sexual Life Cycles Review: Describe the functions of mitosis. High frequency quiz mistakes: Practice D. Draw a triploid nucleus of a cell with n = 2.

  4. Chapter 13 - Meiosis and Sexual Life Cycles Review: Describe the functions of mitosis. High frequency quiz mistakes: 2. What are the two possible chromosome combinations found in human male sperm? - Are the gametes haploid or diploid? Ans: One of each homologous pair 1 through 22 and X 1 through 22 and Y

  5. Chapter 13 - Meiosis and Sexual Life Cycles Review: Describe the functions of mitosis. This brings us to our next adventure…how are the gametes made? Meiotic Cell Division (the other cell division)

  6. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Compare asexual to sexual reproduction Reproduction A. Asexual Reproduction B. Sexual Reproduction

  7. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Compare asexual to sexual reproduction A. Asexual Reproduction 1. One parent 2. Genetically identical offspring (called clones) if we ignore mutations, which they rely on to evolve. Made possible by begin able to have numerous offspring very quickly as positive mutations are rare, but if you have millions of offspring in a few days one likely has such a mutation. What is a positive mutation in general? One that give the organism (vehicle) a better ability to survive and reproduce in current environment. 3. Single-cell organisms (certain protists [ex. amoeba] and fungi [ex. yeast] and all prokaryotes [bacteria]) A. Prokaryotic cell cycle (binary fission) B. eukaryotic cell cycle (“mitosis”) 4. Plants (vegetative propagation) and animals

  8. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Compare asexual to sexual reproduction B. Sexual Reproduction - Two parents - Gametes produced (fertilization) - Highly variable offspring due to mixing of DNA of two parents - Most eukaryotes Tend to have fewer offspring over longer periods of time making mutations not a reliable means of generating diversity… …better to shuffle the DNA between two organisms.

  9. Chapter 13 - Meiosis and Sexual Life Cycles NEW AIM: Describe how gametes are formed. Gametes Somatic cells Fig. 8.13

  10. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. Meiotic cell division 1. Formation of gametes in animals - Therefore essential for sexual reproduction 2. Formation of spores in plants and fungi 3. Called reduction division - The number of chromosomes is cut in half (typically from diploid [2n] to haploid [n])

  11. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. Compare gametes to somatic cells in terms of chromosome number. (Soma- means body; somatic cell = body cell) Gametes are haploid (have one set of 23 chromosomes in humans), while somatic cells are diploid (have two sets or 46 chromosomes in humans)

  12. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. Gametes Somatic cells Fig. 8.13

  13. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Describe the eukaryotic cell cycle. Review the DNA/chromosomes in a human nucleus…

  14. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Describe the eukaryotic cell cycle. Humans have 23 pairs of chromosomes for a total of 46. This image shows the 46 chromosomes from the nucleus of a single human male cell. You can see that each chromosome has a very similar (homologous) matching pair with the exception of the sex chromosomes (X and Y). Females would have a homologous pair of X’s. Males have an X and a Y (not homologous). This display of chromosomes is called a Karyotype.

  15. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Describe the eukaryotic cell cycle. Humans have 23 pairs of chromosomes for a total of 46. Therefore we have how many of each gene? Ans: at least two of every gene, except for the genes on the X and Y chromosomes in males since these chromosomes are not homologous. These are homologous (similar) chromosomes If the gene for hemoglobin were on one of these (green bar), then it is on the other as well in the same location (locus).

  16. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Describe the eukaryotic cell cycle. Humans have 23 pairs of chromosomes for a total of 46. Every nucleus has 22 pairs of autosomes (chromsomes 1 through 22)

  17. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Describe the eukaryotic cell cycle. Humans have 23 pairs of chromosomes for a total of 46. …and one pair of sex chromosomes

  18. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Describe the eukaryotic cell cycle. Humans have 23 pairs of chromosomes for a total of 46. What chromosomes would have been found in the sperm that fertilized the ovum that was to be this person? *One of each pair comes from the mother, and the other comes from the father.

  19. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Describe the eukaryotic cell cycle. Humans have 23 pairs of chromosomes for a total of 46. *Therefore, this is the DNA that would have been packaged in the nucleus of the… (sperm or egg?) …father’s sperm that penetrated and fertilized the ovum to form a zygote because only males have Y chromosomes.

  20. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Describe the eukaryotic cell cycle. Humans have 23 pairs of chromosomes for a total of 46. *And this is the DNA that would have been packaged in the nucleus of the mother’s ovum (has an X). This could also be in a sperm, but the previous slide could not be in an ovum. Explain. Ans: Males are XY. Therefore sperm can have an X or Y (they determine sex. Females are XX and therefore the ovum can only have an X.

  21. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Describe the eukaryotic cell cycle. Humans have 23 pairs of chromosomes for a total of 46. - One of each of chromosomes 1 through 22 and a sex chromosome as shown to the right is considered to be one complete set or n. The word for this is haploid. hap- = one -ploid = set

  22. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Describe the eukaryotic cell cycle. Humans have 23 pairs of chromosomes for a total of 46. If I said that human cells are 2n that means each cell has how many sets? 2

  23. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Describe the eukaryotic cell cycle. Humans have 23 pairs of chromosomes for a total of 46. If I said that human cells are 2n that means each cell has how many sets? 2 The word for this is diploid. di- = 2 -ploid = sets Humans are diploid organisms. What are our gametes, ha- or diploid? Ans: haploid. When they fuse during fertilization the resulting zygote is diploid.

  24. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Describe the eukaryotic cell cycle. What is “n”? n is a complete set of chromosomes (1 of each chromosome) n is called the haploid number …or number of chromosomes in a complete set.

  25. Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cycles AIM: Describe the eukaryotic cell cycle. What is the value of “n” in humans? 23, because we have 23 chromosomes in one set

  26. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. How and where are the gametes formed in humans? Gametogenesis - formation of gametes (two types) 1. spermatogenesis • Formation of sperm, occurs in testes • (male gonads) 2. Oogenesis - Formation of ovum, occurs in ovaries (female gonads) This is all meiosis (gametogenesis, spermatogenesis, Oogenesis)

  27. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. The variety of sexual life cycles

  28. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. Ploidy? n? Meiotic cell division This figure shows a simple diploid cell with one homologous chromosome pair (n=1). Red one is maternal (coming from mother) and blue one is paternal (coming from father). What will happen first?

  29. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. Meiotic cell division DNA will be replicated. Then what?

  30. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. Meiotic cell division Homologous pairs will be pulled apart. And lastly?

  31. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. Haploid (n) Meiotic cell division Sister chromatids will be pulled apart. Haploid (n) Each resulting cell is haploid with one of each homologous pair! Diploid (2n) Diploid (2n) Meiosis I (1st division) Meiosis II (2nd division) If you want to add a second, third or even 23 pairs, they all behave the same way.

  32. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. Meiotic cell division Overview

  33. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. MEIOSIS (meiotic cell division) (Gamete/spore formation)

  34. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. MEIOSIS (meiotic cell division) (Gamete/spore formation) Mitotic cell division (asexual reproduction) would have evolved first before sexually reproducing organisms, which require meiosis, came onto the scene… Reminder: Evolution builds on old ideas (Ex. RNA world hypothesis) You might hypothesize then that meiotic cell division should be very similar to… Mitotic Cell Division. General overview to start…

  35. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. MEIOSIS (meiotic cell division) (Gamete/spore formation, reduction division) Why is it logical to pair up homologous chromosomes? The proteins of the cell are simply programmed to pull paired up chromosomes apart (life is simple, just a lot of simple things happening at once making it appear overly complex)…

  36. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. Meiotic cell division (details): 1. Interphase (G1, S, G2) • - Similar to cell cycle (mitotic cell division) interphase. Use those notes. 2. Meiosis – two rounds of cell division • a. Meiosis I – first round (PI, MI, AI, TI) • b. cytokinesis • c. Interaphase II (interkinesis) - only in certain species (do not need to include this on test) • d. Meiosis II – second round (PII, MII, AII, TII) • IPMATPMAT • e. cytokinesis

  37. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. Interphase (G1, S, G2) • - Similar to cell cycle (mitotic cell division) interphase. Use those notes.

  38. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. MEIOSIS I: Separate the homologous pairs Prophase I (longest phase, up to 90% of meiosis) • -Most complex phase of meiosis • -Occupies 90% of meiotic cell division • Chromosomes condense • Synapsis occurs = homologous chromosomes come together in pairs resulting in the formation of tetrads.

  39. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. MEIOSIS I: Separate the homologous pairs Prophase I • Crossing over occurs – homologous chromosomes exchange equivalent segements • i. This “shuffles” the genes so that the same genes are not always together on the chromosome • ii. This site of crossing over is called the chiasma

  40. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. MEIOSIS I: Separate the homologous pairs Prophase I • -nucleoli disappear • -centrosomes move to poles • Spindle begins to form • Nuclear envelope breaks down • MTs attach to kinetochores at centromeres • -one pole is attached to one homologous pair while the other pole attaches to the other homologous pair • Free MTs interact with each other to elongate cell like in mitosis

  41. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. MEIOSIS I: Separate the homologous pairs Metaphase I • -tetrads align on metaphase plate (brought there by kinetochore motor proteins using ATP for fuel)

  42. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. MEIOSIS I: Separate the homologous pairs Anaphase I • - Homologous pairs (homologs) separate as kinetochore proteins walk along spindle fibers toward opposite poles • - sisters stay together attached by centromere

  43. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. MEIOSIS I: Separate the homologous pairs Telophase I • - Homologs arrive at poles • - Each pole now has a haploid (n) set: remember that sister chromatids are considered a single chromosome Cytokinesis • - Overlaps telophase I • - Similar to cytokinesis in mitotic phase • - Results in two haploid (n) cells although the amount of DNA is similar to the starting diploid cell

  44. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. Haploid after cytokinesis – each cell has one of each homologous pair diploid diploid diploid diploid

  45. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. Meiosis II separate the sisters haploid - Similar to the mitotic phase – separate the sisters - Meiosis II starts with two haploid cells and forms four haploid cells with half the amount of DNA **** Chromosomes do not replicate. Only the centrosomes replicate during interphase II/prophase II

  46. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed.

  47. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. Why go through all of this trouble (use lots of energy) to makes gametes, cross-over, find a mate, try and fertilize an egg to reproduce sexually? Genetic variation/diversity of offspring (sexually reproducing organisms do this to mix/shuffle their DNA resulting in very different offspring genetically so that as the environment changes, there will inevitably be certain gene combinations that will survive it.) Ex. The flu pandemic of 1918 may have killed 50 million people, but it didn’t kill everyone. Different gene combinations means different biochemistry and therefore different susceptibility to disease or other environmental changes. Another example is HIV…

  48. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. Why go through all of this trouble (use lots of energy) to makes gametes, find a mate, try and fertilize an egg…basically to reproduce sexually? Genetic variation/diversity of offspring Evolutionary Trade-offs: realize that it is a trade-off since it does require more energy to do this and time to find a mate, etc… There is almost always a trade-off. Ex) We stand upright on two legs using skeletons naturally selected to walk on all fours. Some of the trade offs are back problems, foot problems, hemorrhoids, and many others…

  49. Chapter 13 - Meiosis and Sexual Life Cycles AIM: Describe how gametes are formed. Irish Potato Famine (another example of the importance of genetic diversity) - Period of mass starvation and disease in Ireland between 1845 and 1852 ~1,000,000 died and another 1,000,000 fled 1/3rd of Irish population depended on potatoes as major source of food. Potatoes do not reproduce well from seed (sexual reproduction) and were asexually propagated (vegetative propagation). Therefore, all the potato plants in Ireland were essentially genetically identical…clones. - Potato blight, a disease that destroys potato plants caused by the fungus Phytophthora infestans, ripped through and destroyed all the Irish crops because all the plants were identical and therefore if one is susceptible to the disease, they all are… Never depend on one crop, especially one crop of genetically identical plants.

  50. Chapter 13 - Meiosis and Sexual Life Cycles NEW AIM: How do sexually reproducing organisms generate diversity? When a human male and female conceive a child, there are greater than 64 trillion possible outcomes (>64 trillion different possible genetic combinations in the offspring) How do sexually reproducing organisms generate this kind of diversity ?

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