Cell Division: Mitosis and Meiosis Explained

1. Unit6 Cell Division Mitosis and Meiosis

2. Cells Life Span

3. Cell Cycle • Chemical messangers called hormones send signals to cells to prepare for division when it is needed.

5. Cell Division • A complex series of changes in the nucleus of a cell that leads to the production of two new cells. • The new cells are called daughter cells.

6. Why do cell divide?? • DNA overload- The cell’s DNA would no longer be able to serve the increasing needs of the growing cell. • Exchange of Materials -If cells grow too large, its more difficult to get rid of waste and take in nutrients.

8. Why do cells divide? • Growth- Humans start off as one cell by the time they are adults they have over 10 trillion cells. • Repair- tissue damage • Reproduction – Asexual or Sexual

9. What is inside of the Nucleus? • Chromosomes are threadlike structures that contain genetic information that is passed on from one generation of cells to the next. • Chromosomes are made up of DNA • Chromosomes are only visible during cell division. Otherwise genetic information is known as chromatin.

10. Chromatin

11. Chromosomes

12. Parts of the chromosome • Centromere - the part of a chromosome that links sister chromatids • Chromatid - one copy of a duplicated chromosome, which is generally joined to the other copy by a single centromere. • Gene segment – segment of gene that codes for a trait

13. Phases of Cell Division • INTERPHASE (G1, S, G2) – growth and preparation, replication of DNA • Mitosis (M) - involves a complex series of changes in the nuclei of body cells that produce identical daughter cells

15. Stages of Mitosis Phase

16. Mitosis Phases • Prophase – Nuclear Membrane becomes invisible and chromosomes condense • Metaphase – Chromosomes line up in the middle • Anaphase – Chromosomes are pulled apart by spindle fibers that attach at the centromere • Telophase – Cell plate forms (plant only), cell membrane pinches in and cytokinesis occurs.

17. During Telophase - Cytokinesis • Dividing of the cytoplasm and the creation of two daughter cells during Telophase

20. The Cell Cycle and Cancer

21. 1.Before a cell divides, the DNA is checked to make sure it has replicated correctly. (If DNA does not copy itself correctly, a gene mutation occurs.) Factors regulating cell cycleThere are several factors that regulate the cell cycle and assure a cell divides correctly.

22. 2. Chemical Signals tell a cell when to start and stop dividing.

23. 3. Neighboring cells communicate with dividing cells to regulate their growth also.

24. What is Cancer? Cancer is a disease of the cell cycle. Some of the body’s cells divideuncontrollably and tumors form.

25. While normal cells will stop dividing if there is a mutation in the DNA, cancer cells will continue to divide with mutation.

26. Tumors in Liver

27. Normal Cell Division DNA is replicated properly. 2. Chemical signals start and stop the cell cycle. 3. Cells communicate with each other so they don’t become overcrowded. Cancer Cells Mutations occur in the DNA when it is replicated. 2. Chemical signals that start and stop the cell cycle are ignored. 3. Cells do not communicate with each other and tumors form. SUMMARY

28. Causes that disrupt the cell cycle • Smoking tobacco • Radiation exposure • Viral infection – HPV • Chemicals

29. Estimated Cancer Deaths in the US in 2013

30. Treating Cancers Cancer treatments include drugs that can stop cancer cells from dividing.

31. MEIOSIS

32. Organisms that reproduce Sexually are made up of two different types of cells. • Somatic Cells are “body” cells and contain the normal number of chromosomes ….called the “Diploid” number (the symbol is 2n). Examples would be … skin cells, brain cells, etc. (Mitosis Cell Division) • Gametesare the “sex” cells and contain only ½ the normal number of chromosomes…. called the “Haploid” number (the symbol is n)….. Sperm cells and ova are gametes. (Meiosis Cell Division)

33. Meiosisis the process by which ”gametes” (sex cells) , withhalfthe number ofchromosomes,are produced. During Meiosis diploid cells are reduced to haploid cells Diploid (2n)  Haploid (n) If Meiosis did not occur the chromosome number in each new generation would double…. The offspring would die.

34. Meiosis Cell Division • Cell division that forms of sex cells (gametes) • Egg cell and Sperm cell (gametes) • 4 daughter cells are made with each having half the number of chromosomes as parent cell (n) Haploid • Reduction of chromosomes • Cells are NOT identical to parent

35. Stages of Meiosis

36. Karyotype - a photograph of a full set of chromosomes “Sex Chromosomes” …….the 23rd set This person has 2 “X” chromosomes… and is a female. 23

37. Homologous Chromosomes • Pair of chromosomes (maternal and paternal) that are similar in shape and size. • Homologous pairs (tetrads) carry genes controlling the same inherited traits. • Each locus(position of a gene) is in the same position on homologues. • Humans have 23 pairs of homologous chromosomes. 22 pairs of autosomes 1 pair of sex chromosomes

38. eye color locus eye color locus hair color locus hair color locus Paternal Maternal Homologous Chromosomes(because a homologous pair consists of 4 chromatids it is called a “Tetrad”)

39. Tetrad nonsister chromatids Crossing Overcreates variation (diversity) in the offspring’s traits. variation

40. Factors that Cause Genetic Variation in Offspring • Crossing Over • Genetic Mutation of DNA

41. Question: • A cell containing 20 chromosomes(diploid) at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?

42. Answer: • 10 chromosomes (haploid)