Reproduction and Development

1. Reproduction and Development

2. Two Types of Reproduction • Asexual Reproduction – 1 parent; organism genetically identical • Sexual Reproduction – 2 parents, organism NOT genetically identical • http://www.bing.com/videos/search?q=bill+nye%2c+greatest+discoveries+clip%2c+the+cell&view=detail&mid=D8D8F0B53BA213103DB8D8D8F0B53BA213103DB8&first=0&adlt=strict

3. Binary Fission • Equal division of the cytoplasm and nucleus of an organism resulting in two new organisms

4. In binary fission,  the chromosome, attached to cell membrane, makes a copy of itself and the cell grows to about twice its normal size • Next, a cell wall forms between the chromosomes & the parent cell splits into 2 new identical daughter cells (clones)

5. Budding • Nucleus of an organism's cell divides equally but the cytoplasm divides unequally

6. Sporulation • The production of spores • What are spores?? - reproductive cell, usually hapliod, dispersed and will not grow until conditions are right

7. Regeneration • The development of an entire new organism from part of an original organism

8. Vegetative Propagation • Regeneration in plants

9. Asexual Reproduction • ** Individuals produced during asexual reproduction are genetically identical to their parent.

10. Cell Division = Mitosis + Cytokinesis • Mitosis – division of the nucleus; used for asexual reproduction in single celled organisms, growth and repair for muti-celled organisms • Cytokinesis – division of the cytoplasm

11. Sexual Reproduction • What is sexual reproduction? • Words to know: • Gametogenesis • Diploid number • Haploid number • Homologous Chromosomes • Gametes • Gonads

12. I. Gametogenesis: the formation of gametes (eggs and sperms) • •Chromosomes exist in pairs in body cells. • •Each species has a characteristic number of chromosomes. • •homologous chromosomes: the 2 members of a pair of chromosomes • -- contain genes for the same traits

13. •diploid number: the number of chromosomes found in the double set of chromosomes found in all body cells (2n) • ** Eggs and sperm contain only 1/2 the diploid number of chromosomes.** • •haploid (monoploid) number: 1/2 the diploid number of chromosomes -- found • in the egg and sperm cells of a species • •gametes: eggs or sperm

14. •gonads: specialized organs in higher animals where the gametes are made • •ovaries: female gonads - are part of the reproductive and endocrine systems • •testes: male gonads - are part of the reproductive and endocrine systems

15. Meiosis – A Source of Distinction Why do you share some but not all characters of each parent? What are the rules of this sharing game? At one level, the answers lie in meiosis.

16. Meiosis does two things - 1) Meiosis takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid). This is a good idea if you’re going to combine two cells to make a new organism. This trick is accomplished by halving chromosome number. In meiosis, one diploid cells produces four haploid cells.

17. 2) Meiosis scrambles the specific forms of each gene that each sex cell (egg or sperm) receives. This makes for a lot of genetic diversity. This trick is accomplished through independent assortment and crossing-over. Genetic diversity is important for the evolution of populations and species.

18. A. What happens??? • 1. The chromosome numbers of a cell produced by meiosis are reduced by 1/2 • 2. haploid nuclei are formed which contain only one chromosome of the original homologous pair. • ** Meiosis ONLY occurs in the gamete producing cells of the gonads.**

19. 3. Ultimately, the diploid chromosome number of a species is maintained from one generation to the next through the processes of MEIOSIS and FERTILIZATION.

20. Meiosis Parent cell – chromosome pair Chromosomes copied 1st division - pairs split 2nd division – produces 4 gamete cells with ½ the original no. of chromosomes

21. The Stages of Meiosis: • A. What happens? • • formation of sex cells occurs • • involves two divisions • • the first is a reduction division -- the second a mitotic division

22. First Meiotic Division • 1. Each single stranded chromosome is replicated during the non dividing resting period. This results in double stranded homologous chromosomes being formed. • 2. Chromosomes shorten and thicken with the spindle apparatus being formed. • 3. Homologous chromosomes pair up side by side in a double line at the equator. (center of the cell) These homologous chromosome pairs are called tetrads. It is here that synapsis and crossing over occurs.

23. Definitions • •synapsis: the meeting of two homologous chromosome pairs • •tetrads: the two pairs of homologous chromosomes • •crossing over: the exchange of chromosome pieces in the tetrad during crossing over. Crossing over increases the variability of the offspring. This is why the offspring of sexual reproduction show many variations.

24. 4. Homologous pairs of chromosomes separate and move toward opposite poles of the cell. • Definitions: • •disjunction: the separation of the homologous chromosome pairs during the first division of meiosis • •nondisjunction: the failure of homologous chromosomes to separate. An example of nondisjunction is Down's syndrome (Mongolian idiocy) results from the nondisjunction of chromosome 21 -- this results in the afflicted individual having an extra 21st chromosome. (an extra chromosome overall as well)Changes in the chromosome number of an individual usually results from nondisjunction.

25. •polyploidy: having an entire extra set of chromosomes . This often will result in the 3n or 4n number of chromosomes. (this makes GREAT BIG strawberries!) • 5. Cytoplasmic division of the cell occurs -- ends the first stage of meiosis (reduction division) • 6. each daughter cell contains the diploid number of chromosomes

26. Meiosis I : Separates Homologous Chromosomes • Interphase • Each of the chromosomes replicate • The result is two genetically identical sister chromatids which remain attached at their centromeres

27. Prophase I • This is a crucial phase for mitosis. • During this phase each pair of chromatids don’t move to the equator alone, they match up with their homologous pair and fasten together (synapsis) in a group of four called a tetrad. • Extremely IMPORTANT!!! It is during this phase that crossing over can occur. • Crossing Over is the exchange of segments during synapsis.

28. Metaphase I • The chromosomes line up at the equator attached by their centromeres to spindle fibers from centrioles. • Still in homologous pairs

29. Anaphase I • The spindle guides the movement of the chromosomes toward the poles • Sister chromatids remain attached • Move as a unit towards the same pole • The homologous chromosome moves toward the opposite pole • Contrasts mitosis – chromosomes appear as individuals instead of pairs (meiosis)

30. Telophase I • This is the end of the first meiotic cell division. • The cytoplasm divides, forming two new daughter cells. • Each of the newly formed cells has half the number of the parent cell’s chromosomes, but each chromosome is already replicated ready for the second meiotic cell division

31. Cytokinesis • Occurs simultaneously with telophase I • Forms 2 daughter cells • Plant cells – cell plate • Animal cells – cleavage furrows • NO FURTHER REPLICATION OF GENETIC MATERIAL PRIOR TO THE SECOND DIVISION OF MEIOSIS

32. Figure 13.7 The stages of meiotic cell division: Meiosis I

33. C. Second Meiotic Division • • similar to mitosis but no chromosome replication occurs • • the diploid number of chromosomes is reduced to the monoploid number in this division

34. Prophase II • Each of the daughter cells forms a spindle, and the double stranded chromosomes move toward the equator

35. Metaphase II • The chromosomes are positioned on the metaphase plate in a mitosis-like fashion

36. Anaphase II • The centromeres of sister chromatids finally separate • The sister chromatids of each pair move toward opposite poles • Now individual chromosomes

37. Telophase II and Cytokinesis • Nuclei form at opposite poles of the cell and cytokinesis occurs • After completion of cytokinesis there are four daughter cells • All are haploid (n)

38. Figure 13.7 The stages of meiotic cell division: Meiosis II

39. D. Results of Meiosis • 1. The diploid number (2n) of chromosomes is reduced by 1/2 to the monoploid number. (n) • 2. Specialized reproductive cells (eggs and sperms) are formed. • 3. The distribution of homologous chromosomes is random -- thus variations frequently occur.

40. One Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment Independent assortment produces 2n distinct gametes, where n = the number of unique chromosomes. In humans, n = 23 and 223 = 6,000,0000. That’s a lot of diversity by this mechanism alone.

41. Another Way Meiosis Makes Lots of Different Sex Cells – Crossing-Over Crossing-over multiplies the already huge number of different gamete types produced by independent assortment.

42. HOW DO MITOSIS AND MEIOSIS COMPARE??? • • Variations rarely occur in MITOSIS. Variations often occur in MEIOSIS. • • Mitosis is associated with growth and asexual reproduction. Meiosis is associated with sexual reproduction

43. Mitosis vs. Meiosis

44. Mitosis vs. Meiosis

45. Meiosis and Sexual Reproduction in Humans • Definitions: • •spermatogenesis -- the production of sperm (one successful meiotic division produces 4 sperm) • •Sperm structure: smaller than the egg or ovum but capable of locomotion with its flagellum • •oogenesis -- the production of ova or eggs (1 egg and three polar bodies are produced in one meiotic division

46. Oogenesis • Egg cells or ova (ovum, singular) are larger , nonmotile cells • Oogenesis is meiosis producing eggs & occurs in the female's ovaries

47. Oogenesis

48. Spermatogenesis • Sperms contain less cytoplasm so they're smaller & have a flagellum to swim to the egg • Spermatogenesis is meiosis producing sperm cells & occurs in the testes

49. Spermatogenesis

50. Review: Meiosis • What is meiosis? -How many divisions? • What does it produce? • ** Meiosis ONLY occurs in the gamete producing cells of the gonads.