1. Chromosomes, Mitosis, And Meiosis
Chapter 8

2. Do Now What is DNA? Where are your chromosomes located?
How many chromosomes do humans have?

3. DNA DNA – deoxyribonucleic acid
Long, thin molecule that stores genetic information
Made up of nucleotide building blocks
(Adenine, Guanine, Cytosine, Thymine)
DNA in a human cell has approximately 6 billion pairs of nucleotides

4. Chromosomes – rod shaped structures made of DNA and protein

5. Chromosomes 1. Contained in nucleus
2. When cell is not dividing, genetic info is kept in uncoiled DNA called chromatin
3. When a cell begins to divide the single DNA molecule coils around proteins called histones to form chromosomes

6. Chromosome Structure
4. Non-histone proteins control activity of specific DNA sequences
5. Each chromosome has two identical parts called – sister chromatids
5. The point at which they meet is called a centromere
6. Division-one chromatid from each chromosome/new cell

7. Info about Chromosomes
1. Entire human genome mapped – found chromosome location of approximately 23,000 genes
2. Above the centromere is the “p” region (small)
3. Below the centromere is the “q” region (large)

8. Chromosome Numbers
1. Every Species has a different number of chromosomes
2. Humans have 46 (23 pairs)
a. 22 autosomes (do not determine the sex)
b. 1 pair sex chromosomes (determine the sex)
3. Females have 2 X chromosomes, males have an X and a Y chromosome

10. Haploid/Diploid
1. Homologous chromosomes (paired chromosomes) are the same size and shape and carry genes for the same traits
2. Cells with both chromosomes of a homologous pair are considered diploid (2N) – body cells - somatic cells
3. Cells with one of the two chromosomes is considered haploid (N) – sex cells

11. Haploid/Diploid

12. Karyotype
An arranged photomicrograph of chromosomes that helps determine problems in chromosome # or deletion
Karyotypes describe the number of chromosomes, and what they look like under a microscope
Attention is paid to:
chromosome length
position of the centromeres
banding pattern
differences between the sex chromosomes

16. Do Now What are chromosomes made of? What does haploid mean?
What does diploid mean?

17. Down’s Syndrome Trisomy 21– 3 copies of chromosome 21 instead of 2
1 in 900 births
More common with older mothers
Some impairment of cognitive ability and physical growth
A particular set of facial characteristics

18. Down’s Syndrome

19. Turner Syndrome Female missing one X chromosome (X0)
1 in every 2500 girls
Infertile – ovaries do not develop
Other female characteristics do not develop
Decreased height

21. Kleinfelter’s Syndrome
Male with an extra X chromosome (XXY)
Occurs in 1 out of every 1700 men
Testicles do not form properly – infertile
Delayed motor function and muscle formation
Increased height, increased tiredness

22. Kleinfelter’s Syndrome

23. II. CELL DIVISION
*Virchow – all cells are derived from pre-existing cells
*Cell division - the process by which cells produce offspring cells
*It is very different for prokaryotes and eukaryotes

24. Cell Division in Prokaryotes
Binary fission – division of a prokaryotic cell into two offspring
Single chromosome copies itself
Cell grows to 2X its size
Cell wall forms between the 2 chromosomes
Each new cell is identical

25. Mitosis - cell division in eukaryotes
Division of a cell’s nucleus that produces a genetically identical cell
It does not change the amount of DNA in a cell
Mitosis occurs in the reproduction of unicellular organisms and in the addition of cells to a tissue or organ of a multicellular organism

26. Cell Cycle Repeating set of events that make up the life of the cell
Consists of:
mitosis - cell division
interphase
G0 Phase – cell exits the cell cycle and does not prepare for another division (nerve cells)

27. Cell Cycle

28. Interphase 1. Takes up 80-90% of cells lifespan
2. Three distinct parts:
a. G1 (Growth Phase) – cell doubles in size, organelles double in number
b. S1 (Synthesis Phase) – chromatin replicates
c. G2 (Growth Phase) - rapid growth phase – prepare for next division

29. Do Now What is cell division in prokaryotes called?
What is cell division in eukaryotes called?
What are the 4 main phases of the cell cycle?

30. Mitosis
1. 4 phases:
Prophase, Metaphase, Anaphase, Telophase

31. Prophase
1. Chromatin coils and forms chromosomes, nucleolus and nuclear membrane disappear, centrosomes and spindle fibers appear

32. Metaphase
1. Chromosomes line up at center, or equator of cell

34. Anaphase
Spindle Fibers pull chromosomes towards poles of cell

35. Telophase 1. Centrioles and Spindle fibers disappear
2. Chromosomes unwind, and nuclear membrane and nucleolus forms in each cell

36. Mitosis in Plant Cells (onion)

37. Cytokinesis 1. Takes place after mitosis
2.Cytoplasm and organelles split and form two daughter cells
3. Each cell receives and identical
copy of the original cell’s
chromosomes and ~ half
of the cytoplasm and organelles

39. Do Now What are the 4 stages of mitosis?
What are the structures that pull the chromosomes toward opposite ends of the cell?
How does cytokenesis differ in animals and plants?

40. Meiosis – reduction division
Process of nuclear division that reduces the # of chromosomes in each new cell to half of the original cell
This is necessary in reproductive cells called gametes so that they can fuse and form a zygote with a normal # of chromosomes
Example – human egg (haploid -1n) and sperm (haploid -1n) form an embryo (diploid -2n)

41. Meiosis A. Two nuclear divisions take place
1. Meiosis I – homologous chromosomes are separated
2. Meiosis II – chromosomes are separated into chromatids for each haploid cell
3. 4 haploid cells are produced - gametes

42. Meiosis I – DNA copies itself just before beginning
Prophase I - similar to mitosis:
DNA coils into chromosomes
nuclear membrane and nucleolus disassemble
spindle fibers appear
THEN
Every chromosome lines up with its homologue and forms a tetrad
Synapsis – pairing of homologous chromosomes – does not occur in mitosis

43. Meiosis Helps Genetic Diversity
A. During Prophase I, homologous chromosomes line up forming a tetrad
B. Chromatids can exchange pieces, called crossing – over
C. Genetic recombination results

44. Meiosis I
Metaphase I
Tetrads line up randomly along the midline of the cell
Spindle fibers attach to centromeres and poles of cell

45. Meiosis I
Anaphase I
Each homologous chromosome moves to an opposite pole of dividing cell
Independent assortment – the random separation of homologous chromosomes
Genetic recombination occurs again due to random separation of maternal (mom’s) and paternal (dad’s) chromosomes

46. Meiosis I Telophase I Chromosomes reach the opposite ends of the cell
Cytokinesis begins
New cells are now haploid (1n):
they contain only one homologue from each homologous pair
But they have two copies of each chromosome because the DNA copied itself right before beginning Meiosis I

47. Meiosis II DNA does not copy itself before Meiosis II
Occurs in both cells formed in Meiosis I
Exactly like mitosis
Results in four new cells from each cell that began Meiosis
Each new cell (haploid – 1n) has half the number of chromosomes as the original cell (diploid – 2n)

48. Gamete Formation
Meiosis produces haploid reproductive cells called gametes
Meiosis only occurs in cells of the reproductive organs
Humans:
Oogenesis - female ovaries produce 1 egg and 3 polar bodies (disintegrate)
Spermatogenesis - male testes produce 4 sperm

49. Oogenesis

50. Spermatogenesis

51. Asexual Reproduction Production of offspring from one parent:
no union of gametes
no genetic diversity
offspring genetically identical
Unicellular organisms -binary
fission or mitosis
Multicellular organisms - budding

52. Sexual Reproduction
Production of offspring through meiosis and the union of egg and sperm
Offspring are genetically different from parents

53. Sexual Reproduction
Except in identical twins, offspring are unique combinations of their parents’ genes

54. Sexual Reproduction
Gives an evolutionary advantage in an environment that can change – survival of the fittest