1. meiosis

2. Review
Every human cell (except 1 type) has 46 chromosomes = Diploid (2n) number.
Since we don’t want more then 46 chromosomes in our cells, then the gametes must have HALF the normal # of chromosomes= HAPLOID (n)

3. a little more…..
So how do we make these cells?
Would mitosis work?

4. MEIOSIS Diploid (2n)  haploid (n)
The form of cell division by which gametes, with half the number of chromosomes are produced.
Diploid (2n)  haploid (n)
Meiosis is sexual reproduction
TWO divisions (meiosis I and meiosis II

5. Sex cells divide to produce gametes (sperm or egg)
The new cells are called Haploid, they have half the number of chromosomes
Meiosis is similar to mitosis with some chromosomal differences

6. Meiosis and gametogenesis
It only happens in the GONADS
(testes and ovaries)
Male: Spermatogenesis
Female: Oogenesis

7. GAMETOGENESIS

8. OOGENESIS

9. SPERMATOGENESIS

10. This produces a fertilized egg = Zygote!

11. Stages of Meiosis I Meiosis needs two divisions!
Main difference between mitosis and meiosis:
Meiosis produces 4 new gametes!
We need 4 gametes every division for GENETIC VARIATION!

12. Genetic variation what are the three sources?
1. Crossing Over
Occurs during Prophase I
2. Independent Assortment
Occurs during Metaphase I
3. Random Fertilization
Sperm joins with the egg cell

13. Crossing Over Crossing over can occur between “nonsister” chromatids
Segments of the chromatids
break and reattach to the other
chromatid

14. Independent assortment
describes how different genes
independently separate from
one another when reproductive
cells develop.
the combinations of traits in the
offspring do not always match the combinations of traits in the parent
Assort randomly at the middle of the cell

15. What can go wrong?
Non disjunction is the failure of chromosome pairs to separate properly during meiosis stage 1 or stage 2
This could arise from a failure of homologous chromosomes to separate in meiosis I, or the failure of sister chromatids to separate during meiosis II or mitosis. The result of this error is a cell with an imbalance of chromosomes.

16. INTERPHASE
Centrioles
Chromatin duplicates

17. PROPHASE 1 chromatin becomes chromosomes
the nuclear membrane disintegrates
homologous chromosomes pair up- crossing over may occur

18. PROPHASE 1 the chromosomes condense the nuclear membrane breaks down
centrioles move to opposite poles of cell & begin making the spindle.
the nuclear membrane breaks down

19. PROPHASE 1
Homologous chromosomes pair up

20. PROPHASE 1
…. and crossing over may occur.

21. PROPHASE 1
centrioles begin building the spindle

22. METAPHASE 1
Pairs of homologous chromosomes line-up at the center of the cell

23. METAPHASE 1 Each pair is assorted independently
So this pair could have
assorted like this
So this pair could have
assorted like this

24. ANAPHASE 1
Homologous pairs of chromosomes are pulled apart.

25. ANAPHASE 1
Sister chromatids remain attached at the centromere

26. ANAPHASE 1

27. TELOPHASE 1
new nuclear membrane forms around each group of chromosomes forming haploid nuclei.

28. TELOPHASE 1
new nuclear membrane forms around each group of chromosomes

29. TELOPHASE 1
cytokinesis occurs

30. CYTOKINESIS 1 Now, BOTH haploid cells will begin Meiosis II
in this division, sister chromatids will separate

31. Meiosis II
Meiosis II is very much like Mitosis

32. PROPHASE 2 the nuclear membrane breaks down
centrioles move to opposite poles of the parent cell

33. PROPHASE 2
the nuclear membrane breaks down

34. PROPHASE 2

35. PROPHASE 2
centrioles begin building the spindle

36. PROPHASE 2

37. METAPHASE 2
The doubled chromosomes move to the equator of the cell

38. ANAPHASE 2
sister chromatids are pulled apart (like in mitosis)

39. ANAPHASE 2

40. TELOPHASE 2
new nuclear membrane forms around each group of chromosomes
cytokinesis occurs

41. TELOPHASE 2
the spindle breaks down

42. TELOPHASE 2
A new nuclear membrane forms around each group of chromosomes

43. CYTOKINESIS 2 Cytokinesis occurs
Four different, haploid cells are formed

44. Chromosomal Disorders
1. Down Syndrome 2. Turner’s Syndrome 3. Klinefelter’s Syndrome

45. Down Syndrome Trisomy: having an extra or 3rd chromosome
Many down syndrome cases can be identified by having an extra chromosome

46. Turner’s syndrome
Women and girls with turner’s, have only one X chromosome
This is an example of monosomy
Symptoms include lack of ovarian development, short stature, webbed neck, arms that turn slightly at the elbow

47. Klinefelter Syndrome
Men and boys with Klinefelter have a Y chromosome and 2 X chromosomes.
This is an example of trisomy
Men and boys are usually tall, and lack secondary sex characteristics such as underarm and facial hair

48. Review of terms Diploid – number of chromosomes in a somatic cell- 46
Haploid/ monoploid- number of chromosomes in a gamete- 23
Homologous chromosome- same size and shape
Gametes- reproductive cells- sex cells
Zygote- the first cells as a result of fertilization of the egg and sperm cell- has a diploid number of chromosomes
Gonads- the organs that make gametes

49. Control of the cell cycle and Stem cells

50. Normal control of the cell cycle
Gene
Segment of DNA that controls the production of proteins
Enzyme
type of protein in all living things that changes the rate of reactions
Production of enzymes is directed by genes
Cyclin
protein that controls the cell cycle and is activates the enzymes

51. Loss of Control of the cell cycle
How?
Failure to produce enzymes
Overproduction of enzymes
Production of the wrong enzyme
-What can happen?
- Cancer: a malignant growth resulting from uncontrolled cell division.

52. Cancer: a mistake in the cell cycle
Results from changes in genes that control the cell cycle
Malignant Tumor
Mass of cancerous cells, can deprive normal cells of nutrients
Metastasis
Cancer cells spread through bloodstream to other organs of the body

53. Causes and prevention Causes Prevention Genetics
Environmental factors ( where you live, cigarette smoke, UV radiation, viral infections)
Prevention
Healthy lifestyle
Diet, avoiding alcohol, drugs, smoking
Protecting from the sun
Cancer screening (pap smear, colonoscopy, mammogram)

54. Stem cells
Embryonic stem cells: unspecialized cells that have the potential to become a wide variety of specialized cells.
Produce every tissue in the body
Found in embryos
Adult Stem Cells
-found in the umbilical cord and bone marrow.
- can produce some different types of cells but not all
Example: bone marrow stem cells can only produce different types of blood cells.

55. Potential uses for stem cells
Cures for diseases
Reverse paralysis caused by spinal cord injury
Organ regeneration