1. Meiosis
Division of Sex Cells

2. Meiosis vocabulary: Diploid
__________ = a cell containing TWO sets of chromosomes
one set inherited from each parent
2n (number of chromosomes)
_____________ (somatic cells)
Diploid
body cells

3. Meiosis vocabulary: Haploid
__________ = a cell with only ONE set of chromosomes.
1n (number of chromosomes)
_____________ (gametes)
Haploid
sex cells

4. Meiosis vocabulary: Gamete __________ = sex cells
_______ = male gamete
_____ = female gamete
Gamete
Sperm
Egg

5. Meiosis vocabulary: _______________
_______________ = paired chromosomes that have genes for the same traits arranged in the same order.
One homologous chromosome is inherited from the organism’s father, the other from the mother.
Homologous
chromosomes

7. Meiosis vocabulary: Meiosis
__________ = a two stage type of cell division that results in gametes with half the number of chromosome number as the body cells.
Meiosis

8. Meiosis vocabulary: Crossing over
_______________ = when nonsister chromatids of homologous chromosomes exchange genetic information
Results in a new combination of genes.
Crossing over

9. Meiosis vocabulary: ___________ = the process of joining gametes.
_________ = when sperm (haploid) fertilizes egg (haploid), the resulting cell is the zygote (diploid)
Fertilization
Zygote

10. I. Genes, Chromosomes and numbers:
In humans, each ______________ (any cell other than a sperm or egg) has ____ chromosomes.
somatic cell 46

11. 46 chromosomes → __________
(humans get ________ from each parent) 23
1 pair

12. XX = ________ XY = ________
_________________ - determine the sex of an individual
Last pair of chromosomes – 23rd pair for humans
XX = ________ XY = ________
Sex chromosomes
female
male

13. A thousand or more genes are lined up on a chromosome at one time.
The _______________________ for an organism is NOT related to the ____________ of that organism!
A thousand or more genes are lined
up on a chromosome at one time.
number of chromosomes
complexity
Ex: A dog has 78 body chromosomes and humans have 46 body chromosomes.

14. Diploid & haploid numbers:
Each ______________ of an organism contains ________ chromosomes
somatic cell
paired

15. Half of each pair came from each parent
Half of each pair came from each parent. These cells are said to have 2n chromosomes or a full set.
They are DIPLOID.

17. Each __________ of organisms contains only _________ a chromosome set.
These cells are HAPLOID and have 1n chromosomes.
Ex: Humans have ____ chromosomes in their gametes (egg or sperm cell)
sex cell
half of 23

18. Sex cells will fuse with another sex cell during fertilization to create an _____________
organism

19. So if human sperm and egg both have ____ chromosomes, after fertilization and embryo has ____ chromosomes! 23 46

20. 2 Reasons why meiosis is significant!!
1. _________ is another form of cell division that ______________________ to be used for reproduction.
Meiosis
creates haploid cells
Female Egg Cell
Male Sperm Cells

21. 2 Reasons why meiosis is significant!!
If mitosis was the only form of cell division, then new offspring would always have _________ as many _____________ as their parents.
2 times
chromosomes

22. 2 Reasons why meiosis is significant!!
Eventually, there would be so many chromosomes, the organism would ____________ or be severely _________.
not survive
mutated

23. 2 Reasons why meiosis is significant!!
2. Meiosis provides ____________________ - the reshuffling of genes carried by the individual members of a population.
GENETIC VARIATION

24. II. Meiosis vs. Mitosis
Remember: _________ = asexual division of diploid body cells
mitosis

25. II. Meiosis vs. Mitosis

27. Meiosis I
Separates __________________ of chromosomes, NOT sister chromatids or individual chromosomes.
homologous pairs

28. Interphase I
Metabolic activities & replicate chromosomes

29. Prophase I __________ occurs – the pairing of homologous chromosomes.
Each pair of ____________ chromosomes come together to form a _________ ( 4 part structure)
Synapsis
homologous
tetrad

30. Genetic material is exchanged in a process called _______________ (swapping portions of adjacent DNA)
crossing over
Must be done with great precision so that neither chromatid gains or loses any genes!

31. Crossing over:

32. 3. Metaphase I
__________________________ line up at the __________ in pairs.
Homologous chromosomes
equator

33. 4. anaphase I
Homologous chromosomes separate and move to opposite ends of the cell.
This occurs because the _____________ do NOT split like in mitosis.
centromeres

34. 4. anaphase I
This ensures that each __________ will receive only ________________ for each homologous pair.
new cell
one chromosome

35. 5. Telophase I
The new cells are _________ so another division is required to create _________ cells.
diploid
haploid

36. Meiosis I: Separate the Homologues

37. Meiosis II
The mechanisms of ____________ is almost the same as _________.
However, the chromosomes DO NOT replicate between meiosis I and meiosis II, the final outcome of meiosis is _________ the number of chromosomes per cell.
Meiosis II
mitosis
halving

38. Allows the new cells to become _________.
1. Interphase II
No replication
______________
Allows the new cells to become _________.
haploid

39. Same as Prophase I except NO _________ are formed. tetrads
2. Prophase II
Same as Prophase I except NO _________ are formed.
tetrads

40. Chromosomes line up at the _________. equator
3. MetapHase II
Chromosomes line up at the _________.
equator

41. ___________________ move to the opposite ends of the cell.
4. Anaphase II
___________________ move to the opposite ends of the cell.
Sister chromatids

42. Creates 4 _________ cells. (gametes) haploid
5. Telophase II
Creates 4 _________ cells. (gametes)
haploid

43. But wait . . . there’s more! Meiosis II: Separate the Sister Chromatids

44. http://www.sumanasinc.com/web content/animations/content/meio sis.html
Meiosis Animation
content/animations/content/meio sis.html

45. Meiosis provides genetic variation in 2 ways
Independent assortment
1. ____________ ____________ of homologous chromosomes during meiosis I
The amount of different chromosomes that can be produced increases greatly as the number of chromosomes an organism has.

46. Meiosis provides genetic variation in 2 ways
A pea plant has 7 pairs of chromosomes. Each pair can line up 2 different ways. Therefore, each gamete can have 27 = 128 possibilities!!
Humans: n=23; so the number of different kinds of eggs or sperms a person can produce is more than 8 million (223).

47. Meiosis provides genetic variation in 2 ways
When fertilization occurs, 223 x 223 zygotes are possible or 70 trillion!!
No wonder brothers and sisters can be so different.

48. Meiosis provides genetic variation in 2 ways
2. ______________ between homologous chromosomes during prophase of meiosis I.
Increases the number of genetic variations.
Crossing over

49. Meiosis is NOT flawless
It is estimated that from 10-20% of all human fertilized eggs contain chromosome abnormalities, and these are the most common cause of pregnancy failure (35% of the cases)

50. These chromosome abnormalities:
Arise from errors in meiosis, usually ________.
Occur more often (90%) during ______________ than during sperm formation.
Become more frequent as a woman _______.
meiosis I
egg formation
ages

51. Down syndrome
Two copies of an autosomal chromosome fail to separate during meiosis so three copies of that chromosome are made.
Trisomy 21

52. Turner’s Syndrome
A female with Turner’s Syndrome usually inherits only one X chromosome.
Women with Turner’s syndrome are sterile which means they are unable to reproduce.

53. Klinefelter’s syndrome
In males nondisjunction may cause Klinefelter’s syndrome, resulting in the inheritance of an extra X chromosome, which interferes with meiosis and usually prevents these individuals from reproducing.

54. Androgen insensitivity syndrome
Every fetus, whether genetically male (XY) or female (XX), starts life with the capacity to develop either a male or female reproductive system.  
In AIS the child is conceived with male (XY) sex chromosomes and normal embryonic testes (known as the fetal gonads) develop and start to produce masculinizing androgens. 
However with AIS, a rare genetic condition carried on the X chromosome means that the fetus has no receptors for these male hormones, and his/her body can't "see" or acknowledge them.  
Lacking the effect of these androgens, the external genitals develop along female rather than male lines.  Unfortunately however, another hormone produced by the fetal testes simultaneously suppresses the development of female internal organs (uterus and ovaries).