OBJECTIVE 6

1. OBJECTIVE 6 • Describe the roles of mitotic and meiotic divisions during reproduction, growth, and repair of cells • Comparing sperm and egg formation in terms of ploidy • Comparing sexual and asexual reproduction

2. Chapter 6: Chromosomes and Cell Reproduction

3. Section 1: Chromosomes

4. Cell Division • Also called cell reproduction • Reasons for cell division: • In unicellular organisms – to reproduce (make a new organism) • In multicellular organisms – for growth, development, repair or replacement of wornout or damaged cells, or to produce gametes (sex cells – eggs and sperm)

5. Binary fission • Type of cell division used by prokaryotes (bacteria) to reproduce • A form of asexual reproduction that produces identical offspring from one parent cell • A single parent passes EXACT copies of all of its DNA to its offspring • Two stages: 1)DNA is copied, 2) the cell divides

6. Binary Fission

7. Terms to Know • Gene – a segment of DNA that codes for a protein or RNA molecule • Chromosomes – structures that contain the DNA and the proteins associated with DNA • Chromatids – 2 exact copies of DNA that make up each chromosome • Centromere – attaches the two chromatids of a chromosome

9. Terms to Know (cont’d) • Somatic cell – body cells (any cell other than a sperm or egg cell) • Gametes – sex cells (eggs and sperm) • Homologous chromosomes – chromosomes that are similar in shape, size, and genetic content • Carry the same set of genes • One from each parent

10. Gametes

11. Homologous Chromosomes

12. Terms to Know (cont’d) • Diploid – contains 2 sets of chromosomes • Somatic cells in humans contain 23 pairs of chromosomes (2n = 46) • Haploid – contains only 1 set of chromosomes • Gametes in humans contain 23 single chromosomes (n = 23) • Fertilization – the process of an egg and a sperm joining together • Zygotes – the first cell of a new organism (a fertilized egg)

13. Haploid/Diploid

14. Zygote

15. Terms to Know (cont’d) • Autosomes – chromosomes that are NOT directly involved in determining the sex (gender) of an individual • 22 of the 23 pairs of human chromosomes • Sex chromosomes – contain genes that will determine the sex of an individual • 1 of the 23 pairs of human chromosomes

16. Autosomes/Sex chromosomes

17. Sex Determination in Humans • Pattern of Sex Chromosomes • XX in females • XY in males • The sex of an offspring is determined by the male • A female can donate only an X chromosome to her offspring. • A male can donate an X or a Y chromosome to his offspring.

18. Human Chromosomes • 2 copies of 23 different chromosomes (total of 46 chromosomes) • Differ in shape, size, and set of genes • Each contains thousands of genes • One set comes from the mother and one from the father

19. Change in Chromosome Number • The presence of all 46 chromosomes is essential for normal development and function. • Monosomy – only one copy of a chromosome • Trisomy – more than 2 copies of a chromosome • Either will cause the baby to not develop properly.

20. Change in Chromosome Number (cont’d) • Down Syndrome (Trisomy 21) • caused by an extra chromosome on the 21st pair • Characteristics – short stature, round face with upper eyelids that cover the inner corners of the eyes, varying degrees of mental retardation • Risk increases greatly in women over 35 • Is caused by nondisjunction – failure of chromosomes to separate during cell division (p. 123) • Karyotype – a photo of chromosomes is a dividing cell that shows the chromosomes arranged by size; can be used to detect abnormalities in chromosome number

21. Karyotype

22. Down Syndrome (Trisomy 21)

23. Down Syndrome

24. Down Syndrome

25. Chromosomal Mutations • Mutations – any change to the structure of a chromosome • Deletion – a piece of a chromosome breaks off completely • Duplication – a chromosome fragment attaches to its homologous chromosome (carries 2 copies of certain genes) • Inversion – chromosome reattaches to the original chromosome but in a reverse orientation • Translocation - chromosome reattaches to a nonhomologous chromosome

26. Section 2: The Cell CycleSection 3: Mitosis and Cytokinesis

27. The Cell Cycle • Cell cycle – a repeating sequence of cellular growth and division during the life of an organism • First Growth (G1) Phase – cell grows; carries out normal functions • Synthesis (S) Phase – DNA is copied (at the end, each chromosome has two chromatids attached at the centromere • Second Growth (G2) Phase – prepare for the nucleus to divide *The first 3 phases are called interphase.

28. Mitosis • The process during cell division in which the nucleus of a cell is divided into two nuclei • Each nuclei ends with the same number and kinds of chromosomes as the original cell.

29. 4 stages: (PMAT) • Prophase • Chromosomes coil up and become visible • Nuclear envelope dissolves • Spindle fibers form between centrioles • Metaphase • Chromosomes line up in the center • Anaphase • Centromeres divide and Chromatids (now called chromosomes) move toward opposite ends • Telophase • Nuclear envelope forms at each end • Chromosomes uncoil • Spindle fibers dissolve • Cytokinesis begins

30. 5. Cytokinesis • The process during cell division in which the cytoplasm divides • Forms two separate cells that are genetically identical

33. Cancer • The uncontrolled growth of cells • A disorder of cell division

34. Chapter 7: Meiosis and Sexual Reproduction

35. Section1: Meiosis

36. Meiosis • A form of cell division that halves the number of chromosomes when forming reproductive cells, such as gametes or spores • Produces 4 haploid sex cells • 2 divisions of the nucleus • Meiosis I (Prophase I, Metaphase I, Anaphase I, Telophase I) • Meiosis II (Prophase II, Metaphase II, Anaphase II, Telophase II)

37. Meiosis

38. Meiosis

39. Keys to Genetic Variation • Independent assortment • Crossing-over • Random fertilization

40. Crossing-Over • Occurs when portions of a chromatid on one homologous chromosome are broken and exchanged with the corresponding chromatid portions of the other homologous chromosome

41. Crossing-Over

42. Independent Assortment • The random distribution of homologous chromosomes during meiosis

43. Random Fertilization • The zygote the forms a new individual is created by the random joining of two gametes

44. Types of Meiosis • Spermatogenesis • Process by which sperm are produced in male animals • Occurs in the testes (male reproductive organs) • Produced 4 haploid cells that change inform and develop a tail to become male gametes (sperm) • Oogenesis • Process by which gametes are produced in female animals • Occurs in the ovaries (female reproductive organs) • One of the four haploid cells receives nearly all of the cytoplasm • Forms 1 female gamete (egg or ovum) and small polar bodies that will not survive

46. Section 2: Sexual Reproduction

47. Asexual Reproduction • A single parent passes copies of all of its genes to each of its offspring • Clone – an individual produced by asexual reproduction; genetically identical to its parent

48. Types of Asexual Reproduction • Binary fission – asexual reproduction by prokaryotes • Fission – the separation of a parent into two or more individuals of about equal size • Fragmentation – body breaks into several pieces; some or all of the fragments later develop into complex adults when missing parts are regrown • Budding – new individuals split off from the parent and become an independent organism, or it may remain attached to the parent

49. Sexual Reproduction • Two parents each from reproductive cells that have one-half the number of chromosomes • A diploid mother and father produce haploid gametes, which join to form diploid offspring • Offspring has traits of both parents (not exactly like either parent)