1. Meiosis and Sexual Reproduction

2. It’s all about chromosomes
What are chromosomes?
A structure composed of DNA, that contains the genetic material

4. There are ________ chromosomes in a human body cell
Sperm cells and egg cells[also called gametes] have half the normal number of chromosomes
The sperm cell has ________ chromosomes
The egg cell has ________ chromosomes

5. Remember, each gamete only has half the normal number of chromosomes
a cell that has half the normal number is called haploid [gametes; egg cells]
A cell that has double the amount of the haploid cell is called diploid [body cell]

6. The human haploid number is _____
The human diploid number is _____
The diploid number of a fire breathing yeti is 50, what’s the haploid number?
the haploid number of a flying Liger is 74, what’s the diploid number?

10. Each diploid cell has a set of homologous chromosomes
Homologous chromosomes: A pair of chromosomes that contain the same gene sequences, one of the pair is derived from the mother and the other from the father.

13. In order to examine chromosomes, they are prepared as a karyotype
A karyotype is a display of chromosomes arranged in homologous pairs

17. How are Karyotypes prepared?
They are prepared from isolated somatic cells, which are treated with a drug to stimulate mitosis and then grown in a culture for several days
Cells arrested in metaphase, are stained and then viewed with a microscope equipped with a digital camera

18. An image of the chromosomes is displayed on a computer monitor
Digital software is used to arrange them in homologous pairs

19. Application Technique Pair of homologous duplicated chromosomes
Centromere
5 µm
Sister
chromatids
Metaphase
chromosome
Figure 13.3 Research method: preparing a karyotype

20. Why is it important to study the karyotype of chromosomes?

21. Screen for defective chromosomes
Karyotyping can be used to:
Screen for defective chromosomes
Screen for abnormal numbers of chromosomes
See the gender

22. gametes The sperm and egg cells are called gametes
The forming of gametes is called gametogenesis

23. The formation of sperm cells is called spermatogenesis
The formation of eggs cells is called oogenesis

26. Your body has special cells in the reproductive organs that are called germ cells.
These cells are the only cells that can undergo meiosis and become gametes such as sperm and ova.

27. 17

28. Meiosis
A process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.

30. Meiosis stages: Meiosis 1
It’s the first cell division in this process
It’s called reduction division
During this process, the chromosome number is halved

31. Interphase
It’s the same interphase as mitosis which consist of 3 parts….
What are they?

32. Prophase 1 the nucleus membrane disintegrates
The centrioles move to opposite sides of the cell while forming spindle fibers

33. The homologous chromosomes pair up in a process called synapsis:
Synapsis is the pairing of homologous chromosomes, one from each parent,  during early meiosis

34. during synapsis, a process called crossing-over occurs
Crossing-over: the process where homologous chromosomes exchange different segments of their genetic material

35. Crossing over creates new combinations of genes in the gametes that are not found in either parent, contributing to genetic variation.

37. Prophase 1

38. Metaphase 1 Now the chromosomes line up down the middle of the cell
This time not in a single file, they’re lined up in homologous pairs

39. Metaphase 1

40. Anaphase 1
The spindle fibers pull the homologous chromosomes away from each other

41. Anaphase 1

42. Telophase 1
2 Nuclei form
The cell “pinches in”

43. Cytokinesis 1
The cell separates into 2 cells, each with 23 chromosomes

44. End of meiosis 1 Meiosis 1 results in two haploid cells.
Each cell has half the number of chromosomes as the original cell[23 chromosome each].

45. Meiosis 2 Also passes through 4 stages
The chromosome number is not being reduced
Now the chromatids from each double-stranded chromosomes are being separated

46. Prophase 2

47. Metaphase 2
The chromosomes line up down the middle of the cell.

48. Anaphase 2
Sister chromatids separate and move to opposite ends of the cell.

49. Telophase 2
Four nuclei form around chromosomes

50. Cytokinesis 2 The cytoplasm splits
The cells divide into 4 haploid cells

52. Gamete Formation In males, meiosis results in 4 sperm cells
In females, meiosis results in 1 egg cell and three polar bodies, which are not used in reproduction.

53. What is the purpose of polar bodies during oogenesis?
 they ensure that the ovum will have most of the cytoplasm.
They rid the body of defective sets of chromosomes, leaving the "good" set within the ovum.
Then they dissolve

56. The sexual life cycle process involved in human reproduction is:
Meiosis
Fertilization
Mitosis of the zygote
differentiation
The sexual life cycle process involved in human reproduction is:

59. Mitosis vs Meiosis mitosis meiosis 1 division occurs during mitosis
2 sets of divisions occur during meiosis
DNA replication occurs during interphase
DNA replication occurs once before meiosis 1
Synapsis of homologous chromosomes does not occur
Synapsis of homologous chromosomes occurs during prophase 1
2 identical cells are formed per cell cycle
4 haploid cells(n) are formed per cell cycle
2 Daughter cells are genetically identical
The daughter cells are not genetically identical because of crossing over
Mitosis occurs only in body cells
Meiosis occurs in reproductive cells
Mitosis is involved in growth and repair
Meiosis is involved in the production of gametes and providing genetic variation in organisms

61. Why is meiosis important?
It maintains the normal species chromosome number by making haploid gametes
It increases genetic variability by recombining genes in eggs and sperm

62. Terms 1. crossing-over 2. recombination 3.independent assortment
4. chromosomal abnormalities
5. differentiation

63. 1. Crossing - over
When homologous chromosomes exchange genetic pieces during prophase 1 of meiosis

65. 2. recombination
When a new combination of genes are made on a chromosome during crossing-over

66. The results of recombination are:
A new combination of inheritable traits
Genetic variation

68. 3. Independent assortment
Each time a body cell goes through meiosis to make a gamete, all the chromosomes line up a different way during the metaphase part
The number of different ways they line up is independent assortment

71. 4. Chromosomal abnormalities
When there’s an incorrect number of chromosomes in a gamete
Can cause birth defects or the zygote fails to develop

72. 5. differentiation
The process by which cells in an embryo develop a specialized form and function
It occurs during the 5th week of pregnancy