1. Chapter 19
Chromosomes and Cell Division

2. FIGURE 19.1
The human life cycle

3. Human Chromosomes Homologous chromosomes: one maternal & one paternal
Sex chromosomes: X & Y
Autosomes: the 22 pairs of chromosomes other than X & Y

4. Chromosomes Consist of DNA and Protein
Genes
genes/chromosome
Most genes code for a protein
Mutation causes change in nucleotide sequence of DNA
Somatic cells (Non-germ cells) have 46 chromosomes (23 pairs)

5. Most people have 23 chromosomes 46 chromosomes 23 pairs of chromosomes

6. Most people have 23 chromosomes 46 chromosomes 23 pairs of chromosomes

7. FIGURE 19.6b
Chromosomes in dividing cells can be examined for defects in number or structure. (b) A karyotype constructed by arranging the chromosomes from photographs like the one in part a. The chromosomes have been arranged on the basis of location of centromere and size.

8. Figure: 19-02
Title:
A map of a human chromosome.
Caption:
Each chromosome contains a specific assortment of genes in a specific location along the chromosome. Genes are often identified through the disease caused when they do not function normally.

9. FIGURE 19.3
Changes in chromosome structure because of DNA replication during interphase and preparation for nuclear division in mitosis.

10. FIGURE 19.3 part 1
Changes in chromosome structure because of DNA replication during interphase and preparation for nuclear division in mitosis.

11. Chromosomes are composed of
DNA
Genes
Chromatin
All of the above
None of the above

12. Chromosomes are composed of
DNA
Genes
Chromatin
All of the above
None of the above

13. During Cell Division (Mitosis) Cells Replicate Their Chromosomes

14. DNA Replication (synthesis)
Precedes cell division
DNA polymerase (enzyme) catalyzes DNA synthesis
Necessary to maintain 46 chromosomes/cell

15. Figure: 19-04
Title:
Changes in chromosome structure because of DNA replication during interphase.
Caption:

16. Overview of Mitosis
FIGURE 19.4
An overview of mitosis

17. Cell Division
During metaphase the chromosomes form a line at the center of the cell

18. FIGURE 19.5 part 1
The stages of cell division (mitosis and cytokinesis) captured in light micrographs and depicted in schematic drawings

19. FIGURE 19.6a
Chromosomes in dividing cells can be examined for defects in number or structure. (a) Photomicrograph of metaphase chromosomes from a human white blood cell.

20. FIGURE 19.5 part 2
The stages of cell division (mitosis and cytokinesis) captured in light micrographs and depicted in schematic drawings

21. Cytokinesis Occurs Toward the End of Mitosis
Phase when Cytoplasm divides
Microfilaments act like purse string

22. FIGURE 19.7 part 1
Cytokinesis is the division of the cytoplasm to form two daughter cells.

23. FIGURE 19.7 part 2
Cytokinesis is the division of the cytoplasm to form two daughter cells.

24. Meiosis

25. Meiosis Forms Haploid Gametes
Occurs in gonads (ovary and testes)
Two Major Accomplishments of Meiosis
Reduce chromosome number of gametes by ½
Shuffle the chromosomes and genes
This increases genetic variability in the population

26. Meiosis Forms Haploid Gametes
Keeps the chromosome number constant through generations and
Increases genetic variability in the population
Meiosis involves two cell divisions

27. Overview of Meiosis FIGURE 19.8
Overview of meiosis. Meiosis reduces the chromosome number from the diploid number to the haploid number. Meiosis involves two cell divisions.

28. The following is accomplished during meiosis
Two identical cells are produced
Four identical cells are produced
The chromosome number is doubled
The genes are shuffled
The number of chromosomes in the resulting cells is halved

29. The following is accomplished during meiosis
Two identical cells are produced
Four identical cells are produced
The chromosome number is doubled
The genes are shuffled
The number of chromosomes in the resulting cells is halved

30. Comparison of Spermatogenesis and Oogenesis

31. FIGURE 19.9
Comparison of spermatogenesis and oogenesis. Meiosis results in haploid cells that differentiate into mature gametes. Spermatogenesis produces four sperm cells that are specialized to transport the male's genetic information to the egg. Oogenesis produces up to three polar bodies and one ovum that is packed with nutrients to nourish the early embryo.

32. Mammalian Egg With Polar Bodies

33. Meiosis and Mitosis Compared

35. TABLE 19.1
MITOSIS AND MEIOSIS COMPARED

36. Crossing over and independent assortment cause genetic recombination (gene shuffling) during meiosis

37. Crossing Over
FIGURE 19.13
Crossing over. During synapsis, when the homologous chromosomes of the mother and the father are closely aligned, corresponding segments of nonsister chromatids are exchanged. Each of the affected chromatids has a mixture of maternal and paternal genetic information.

38. Independent Assortment
FIGURE 19.14
Independent assortment. The relative positioning of homologous maternal and paternal chromosomes with respect to the poles of the cell is random. The members of each homologous pair orient independently of the other pairs. Notice that with only two homologous pairs, there are four possible combinations of chromosomes in the resulting gametes.

39. Number of different gametes produced by humans
23 pairs of chomosomes
Each pair line up randomly on the metaphase plate
Therefore 223 different combinations =
> 8,000,000 different gametes from each person

40. Gene shuffling during meiosis is caused by:
Crossing over of chromosomes
Independent assortment of chromosomes
Nondisjunction of chromosomes
Cytokinesis
Condensation of chromosomes

41. Mistakes Sometime Happen During Meiosis
Failure of chromosomes to separate during meiosis creates cells with extra or missing chromosomes
Called Nondisjunction of Chromosomes

42. FIGURE 19.15
Nondisjunction is a mistake that occurs during cell division in which homologous chromosomes or sister chromatids fail to separate during anaphase. One of the resulting daughter cells will have an extra copy of one chromosome, and the other will be missing that type of chromosome.

43. Examples of Nondisjunction
Down syndrome (three # 21 chromosomes)
Turner syndrome (one X chromosome)
Klinefelter syndrome (XXY)

45. Missing or extra sex chromosomes cause Turner syndrome and Klinefelter syndrome. (a) A female with Turner syndrome has one rather than the normal two X chromosomes. Because the ovaries are underdeveloped, she is usually infertile. (b) A male with Klinefelter syndrome is XXY. Klinefelter syndrome is characterized by small testes (and sometimes breast enlargement).