Sexual Reproduction in Living Organisms

1. Chapter 4: Reproduction of Organisms Life Science 7th grade

2. Inquiry • Do you think ALL living things have two parents? • What might happen if the penguins (on the chapter cover photo) did not reproduce? • Why do you think living things reproduce?

3. Bell work Ch4. L1 • Sexual reproduction: reproduction in which the genetic materials from two different cells combine, producing an offspring. • Egg: female sex cell that forms in the ovary. • Sperm: male sex cell that forms in the testis. • Fertilization: the process during which an egg cell and a sperm cell join together to form a new cell. • Zygote: The new cell that is formed as a result of fertilization. • Diploid cell: Cells that have pairs of chromosomes • Homologous chromosomes: pairs of chromosomes that have genes for the same trait arranged in the same order • Haploid cell: Cells that only have one chromosome from each pair • Meiosis: The process by which one diploid cell divides to make four haploid cells

4. Launch Lab (work in pairs) • Each pair gets one “male parent” and one “female parent bag” • Without looking in the bag, select three beads from each bag. • Record bead colors from each bag • The six beads you pulled represent one offspring (x4) • Put beads back in respective bags after each offspring 1- How are the offspring similar? How are they different? 2- Why were there differences between offspring? Are differences beneficial? Why or why not?

5. What is sexual reproduction? • Reproduction in which the genetic materials from two different cells combine, producing an offspring. • Those cells are called sex cells • Sex cells form in reproductive organs • What are sex cells in humans and where do they form?

6. Sex cells • Egg • Female sex cell • Forms in ovary • Sperm • Male sex cell • Forms in testis

7. Fertilization • An egg cell and a sperm cell join together • This forms a new cell • Zygote= new cell that forms from fertilization • Develops into an organism • What process is responsible for the development of a zygote into an organism?

8. Diploid cells • Cells that have pairs of chromosomes • Similar chromosomes occur in pairs • This happens in body cells • Diploid cells are produced via mitosis • Video

9. Chromosomes • Homologous chromosomes: pairs of chromosomes that have genes for the same trait arranged in the same order • One from mom, one from dad make up a pair • *****NOT IDENTICAL= DIFFERENT FROM SISTER CHROMATIDS.****** DO YOU THINK A MORE COMPLICATED ORGANISM HAS MORE CHROMOSOMES THAN A SIMPLER ORGANISM?

10. How many chromosomes? • Human body cells have 23 pairs of chromosomes= 46 total chromosomes • Number of chromosomes does NOT correlate with how complicated an organism is • Dog has 78, Fern has 1,260 chromosomes

11. Haploid cells • Cells that only have one chromosome from each pair (in humans have 23 total, not 46 total) • Sex cells are haploid • Haploid cells are produced via meiosis

12. Meiosis overview • Many similarities to mitosis • Mitosis+cytokinesis = ONE division of nucleus + one division of cytoplasm • End result= Two diploid cells • Meiosis= TWO divisions of nucleus and TWO divisions of cytoplasm • End result= FOUR haploid cells • Happens in two phases- meiosis I and meiosis II

13. Meiosis - phases • Interphase- EXACTLY THE SAME AS IN MITOSIS. Period of growth and replication. Chromosomes are duplicated and each duplicated chromosome has two sister chromatids joined at the centromere. • This only happens once

14. Meiosis I - phases • Prophase I: chromosomes condense, homologous chromosomes form pairs. Nuclear envelope breaks apart, nucleolus disappears.

15. Meiosis I - phases • Metaphase I: Homologous chromosomes line up along the middle of the cell. Spindle fiber attaches to centromere.

16. Meiosis I - phases • Anaphase I: Chromosomes pairs (homologous chromosomes) are pulled apart. SISTER CHROMATIDS STAY TOGETHER.

17. Meiosis I - phases • Telophase I: Nuclear membrane reappears around PAIRS of chromosomes, nucleolus reappears. Cytoplasm divides through cytokinesis. Two daughter cells form.

18. Meiosis II - phases • NO SECOND INTERPHASE. Daughter cells from meiosis I immediately undergo meiosis II • Prophase II: Because no replication, chromosomes stayed as thick sister chromatids • Nuclear envelope breaks down • Nucleolus disappears.

19. Meiosis II - phases • Metaphase II: • Sister chromatids line up along the middle of the cell • Spindle attaches to centromere.

20. Meiosis II - phases • Anaphase II: Sister chromatids pulled apart and move toward opposite ends of the cell

21. Meiosis II - phases • Telophase II: • Nuclear membrane forms around chromosomes • cytoplasm divides via cytokinesis. • Result= four haploid cells.

22. Meiosis summary

23. Why is meiosis important? • Maintains diploid cells • When haploid cells join (via fertilization) they make a diploid cell= zygote. • Zygote then divides via mitosis to make the organism • Creates haploid cells • Maintains correct number of chromosomes in sex cells so when they join, they form a zygote with the correct number of chromosomes

24. Mitosis vs Meiosis (table p.122)

25. Advantages of sexual reproduction • Genetic variation • Inherit different genes from parents compared to siblings • Occurs in all organisms that reproduce sexually • Includes plants • Selective breeding • Choose the traits you like (breed individuals with those traits) and over time those can become dominant • Video

26. Disadvantages of sexual reproduction • Takes time and energy • Search for mate can be problematic • Expose to predators, disease or harsh environments • Limitations • Gestational period (pregnancy) • Can’t get pregnant while already pregnant, have to wait for one to finish before can start another one ONE STEP UP: Can you think of a way some organisms overcome the gestational limitation?

27. HOMEWORK Ch4 L.1 • Vocabulary words on flash cards • Memorize for quiz • Lesson review questions p.126 #1-10 • Outline lesson 1 • Quiz lesson 1

28. Meiosis lab p.138 • Let’s recreate mitosis and meiosis using pool noodles • 8 volunteers to be chromosomes • Each person gets one • 8 volunteers to be nuclear envelope • Surrounds chromosomes • 8 volunteers to be spindle • 8 volunteers to be narrators/puppeteers

29. Bell Work Ch4 L.2 • Asexual reproduction: the process by which one parent organism produces offspring WITHOUT meiosis and fertilization • Fission: cell division in prokaryotes that forms two genetically identical cells • Budding: the process by which a new organism grows by mitosis and cell division on the body of its parent. • Regeneration: occurs when an offspring grows from a piece of its parent • Vegetative reproduction: a form of asexual reproduction in which offspring grow form a part of a parent plant • Cloning: a type of asexual reproduction performed in a laboratory that produces identical individuals from a cell or from a cluster of cells taken from a multicellular organism

30. Yeast launch lab p.129 • I warmed water to 34˚C (93˚F) • I added 5g yeast and 5g sugar • What does the mixture look like initially? After 5 minutes? • Drop of solution onto slide (cover with cover slip) • Draw what you see under microscope. • Evidence of reproduction? • TURN THIS IN

31. What is asexual reproduction? • One parent organism produces offspring WITHOUT meiosis and fertilization. • Inherit all DNA from one parent • What are some advantages/disadvantages of reproducing this way? • Mold: a type of fungus that can reproduce sexually OR asexually. (fuzzy stuff on old food) • Bacteria, protists, plants and some animals can reproduce asexually ONE STEP UP: How do parent/daughter cells compare to each other in asexual reproduction?

32. Types of asexual reproduction • Fission: cell division in prokaryotes that forms two genetically identical cells. • Prokaryote’s DNA is copied • Each copy attaches to cell membrane • Cell elongates, pulling copies of DNA apart • Cell membrane pinches inward along middle of the cell • Cell splits and forms two new identical offspring • Example: E.coli

33. Types of asexual reproduction • Mitotic cell division: used by unicellular eukaryotes • Organism produces two offspring through mitosis and cell division • Example: amoeba

34. Types of asexual reproduction • Budding: a new organism grows by mitosis and cell division on the body of its parent. • Bud is genetically identical to parent • When bud gets big enough, it can break off from parent • Example: hydra (multicellular organism), yeast (unicellular organism).

35. Types of asexual reproduction • Animal regeneration: occurs when an offspring grows from a piece of its parent. (varies greatly among animals) • Producing new organisms: each new organism is identical to starting organism • Example: planarian (can cut in half and each half makes a new organism), sea star (can cut an arm and if it contains part of central disk and conditions are right, that arm will make a whole new star)

36. Types of asexual reproduction • Animal regeneration cont’d • Producing new parts: regeneration • Common in animals. Humans can regenerate skin or liver, some animals can regenerate limbs. • THIS IS NOT CONSIDERED ASEXUAL REPRODUCTION BECAUSE IT DOES NOT PRODUCE A NEW ORGANISM

37. Types of asexual reproduction • Vegetative reproduction: a form of asexual reproduction in which offspring grow form a part of a parent plant. • Parent plant can grow long stems called stolons • If a stolon touches the ground, it forms roots. • Once roots are down, a new plant can grow. • If stolon is broken from parent plant, the new plant can survive on its own. • Example: strawberries, raspberries and potatoes.

38. Types of asexual reproduction • Cloning: a type of asexual reproduction performed in a laboratory that produces identical individuals from a cell or from a cluster of cells taken from a multicellular organism.

39. Types of asexual reproduction • Plant cloning: do via tissue culture. • Use cells from meristem to grow new plants in lab • Animal cloning (Example: sheep) • Take cell from sheep 1, take unfertilized egg from sheep 2 • Remove DNA from unfertilized egg (it’s an empty egg now) • Fuse cell from sheep 1 with empty egg from sheep 2 • Cell develops into embryo in laboratory • Implant embryo into sheep 2 • Sheep 2 gives birth to clone of sheep 1 • Video

40. Advantages of asexual reproduction • Don’t need a mate • Rapidly produce a large number of offspring

41. Disadvantages of asexual reproduction • Genetically identical to parent= little variation within a population • Variation can give better chance of survival • Mutations • Harmful mutations will be passed on to all offspring

42. HOMEWORK Ch4 L.2 • Vocabulary wordsß on flash cards • Memorize for quiz • Lesson review questions p.137 #1-9 • Outline lesson 2 • Quiz lesson 2 • OPTIONAL: Extra credit (due on test day) p.141-145 (all) • You MUST write the entire question and answer down for credit. Only answers will NOT be accepted.