Biology

1. Biology Chapter 8 Cell Reproduction Mitosis and Meiosis

2. Objectives • Explain the nature of cell division • Discuss the significance of mitosis • Identify and describe the phases of mitosis • Distinguish between sexual and asexual reproduction • Describe the forms of asexual reproduction • Define meiosis and its importance to sexual reproduction • Describe the major differences between mitosis and meiosis

3. Pennsylvania State Standards • S11.A The Nature of Science • S11.A.1 Reasoning and Analysis • Assessment Anchor • S11.A.1.3 Describe and interpret patterns of change in natural and human-made systems. • Eligible Content • S11.A.2.1.3 Use date to make inferences and predictions, or to draw conclusions, demonstrating understanding of experimental limits. • S11.A.3.2.1 Compare the accuracy of predictions represented in a model to actual observations and behavior. • S11.B Biological Sciences • S11.B.1 Structure and Function of Organisms • Assessment Anchor • S11.B.1.1 Explain structure and function at multiple levels of organization • Eligible Content • S11.B.1.1.3 Compare and contrast cellular processes (e.g., photosynthesis and respirations, meiosis and mitosis, protein synthesis and DNA replication). • S11.B.2.2.1 Describe how genetic information is expressed(i.e. DNA, genes, chromosomes, transcription, translation, and replication) • S11.B.2.2.2 Compare and contrast the functions of mitosis and meiosis in passing on genetic information.

4. Chapter 8 Cell Reproduction • 8-1 Chromosomes • 8-2 Cell Division • 8-3 Meiosis

5. Focus Concept Cell reproduction perpetuates life, It allows for the growth and reproduction of organisms, and passes genetic information to future generations.

6. 8-1 Chromosomes: • Chromosome Structure • Chromosome Numbers • Diploid and Haploid Cells

7. The Chromosome • Threadlike structure within a cell which contains the genetic information that is passed on from one generation of cells to the next. • The are located in the nucleus of a cell. • Human somatic cells contain 46 chromosomes (or 23 pairs) • Somatic cells – normal body cells • Gametes – reproductive cells (sperm and egg) • Filling the activity of specific regions of the DNA

8. Chromosome Structure • Chromatin – the genetic material that makes up chromosomes. • Chromatin is composed of DNA and proteins • The DNA is super-coiled into a very compact structure during cell division. • Histones: proteins that help maintain the shape of the chromosome and aids in the tight packing of DNA • Nonhistone: do not participate in the packing of DNA. Involved in contro

9. Chromosome Formation • During cellular division, chromatin condenses or coils to form the rod-like chromosomes. • The DNA double helix begins to coil and wrap tightly around proteins(histones) to form a nuclesome. • Nucleosome – DNA which is tightly wrapped around histones. • The nuclesome then begins to twist up to form coils. • The coils then begin to twist to form larger coils called super coils. • Super coils – large coils of nuclesome coils which make up chromosomes. • Each chromosome consists of two halves, each is referred to as a chromatid.

14. Chromatids • Each identical half of a chromosome • Form as the DNA makes a copy of itself before cell division • Each new cell receives one chromatid from each chromosome.

15. Centromere • Constricted area of each chromatid • Helps hold the two chromatids together • Aids in movement of chromosomes during cell division.

16. Chromatin • Less tightly coiled DNA-protein complex. • Regions of DNA uncoil between cell divisions so information can be read and used to direct the activities of the cell.

18. Prokaryote DNA • Bacterial DNA is simpler than eukaryotes. • Usually only one chromosome which is attached to the inside of the cell membrane • Consists of a circular DNA molecule and associated proteins.

20. Chromosome Numbers • Each species has a characteristic number of chromosomes in each cell. • Chromosome number does not indicate species complexity. • The human chromosome number is 46 or 23 pairs.

21. Sex Chromosomes • Chromosomes that determine the sex of an organism. • May also carry genes for other characteristics. • Either X or Y. • Normal females XX • Normal males XY

22. Autosomes • All of the other chromosomes in an organism • Humans: 2 sex chromosomes + 44 autosomes = 46 total chromosomes

23. Homologous Chromosomes • Occurs in Meiosis diploid cells • Also called Homologues or homologous pairs • Every cell of an organism produced by sexual reproduction has 2 copies of each autosome. • One copy is received from each parent • Same size, shape and carry genes for the same traits.

24. Sister Chromatids • Each duplicated chromosome is made up of two halves. Each half is referred to as a sister chromatid. • Sister chromatids – (occur during mitosis) and the DNA they contain are exact copies of each other. • Formed when DNA is copied during interphase.

26. Karyotype • A photomicrograph of the chromosomes in a dividing cell.

28. Chromosomal Abnormalities • Deletion: a portion of a chromosome is lost • Duplication: the deletion becomes incorporated into its homologue so that the segment appears twice on the same chromosome.

29. Inversion • Translocation

30. Chromosomal Abnormalities • Nondisjunction: the failure of chromosomes to separate properly during meiosis. Results in too many or too few chromosomes. • Trisomy: an abnormality in which a cell has an extra chromosome or section of a chromosome

31. Nondisjunction

32. Female with only one X chromosome XO Turner Syndrome

33. Male with two X chromosomes XXY Klinefelter Syndrome

34. Other Sex Chromosome Aneuploidies • XYY genotype - taller than average; after about age 35, extra Y often degenerates and is not passed on to offspring. • XXX genotype - some developmental deficiencies; some instances of mental retardation

35. Trisomy 21 Down Syndrome Link to website with other chromosomal abnormalities

36. Diploid Cells (2n) • Cells having 2 sets of chromosomes. Have both chromosomes from each homologous pair. • All normal human cells (body cells) except reproductive cells are 2n

37. Hapliod (1n) • Contain only one set of chromosomes. • Have only half the number of chromosomes that are present in diploid cells. • Sperm and egg cells (gametes) are 1n

38. Fertilization • When a sperm cell (1n) and an egg cell (1n) combine to create the first cell of a new organisms it becomes 2n. • If the reproductive cells were diploid, the new cell would have too many chromosomes and would not be functional.

39. 8-2 Cell Division • Cell Division in Prokaryotes • Cell Division in Eukaryotes

40. Cell Division in Prokaryotes • Binary Fission: the division of a prokaryotic cell into two different offspring cells. • Consists of three stages. (Fig.8-4 p148)

42. Cell Division in Eukaryotes • Mitosis and Cytokinesis: cellular division that results in new cells with genetic material identical to the original cell. • Occurs in: • the reproduction of unicellular organisms • the addition of cells to a tissue or organ in a multicellular organism (growth, repair)

43. The Cell Cycle • The repeating set of events that make up the life of a cell from mitosis to mitosis.. • Cell division is one phase of the cell cycle. (includes both mitosis and cytokinesis) • Interphase: the time between cell divisions. The cell spends most of its life in interphase. • IPMATC

44. Cell cycle animation

45. Interphase • G1 phase: offspring cells grow to mature size. The time “gap” following cell division and preceding DNA replication • S phase: the cell’s DNA is copied, “synthesized” • G2 phase: the time “gap” following DNA synthesis and preceding cell division. Growth and preparation for division. • G0 phase: cells can enter this state when fully developed. Do not copy DNA and do not divide. Ex. Central nervous system cells.

47. Mitosis / M phase • The equal division of the nucleus • Continuous process that can be divided into 4 phases: • Prophase • Metaphase • Anaphase • Telophase • PMAT

49. Prophase: • 1st phase of mitosis • Shortening and tight coiling of DNA into rod-shaped chromosomes which are visible with a light microscope • The 2 copies of each chromosome stay connected to one another by the centromere

50. The nucleolus and nuclear membrane break down and disappear • Centrosomes appear next to the disappearing nucleus. • In animal cells, each centrosome contains a pair of small cylindrical bodies called centrioles. Not present in plants. • The centrosomes move toward opposite poles of a cell • Spindle fibers (made of microtubules) radiate from the centrosomes. Called mitotic spindles and help to equally divide the chromatids between the two offspring cells.