1. Meiosis

2. Chromosomes (X’somes)
chromosomes come in ____

3. Chromosomes (X’somes)
chromosomes come in pairs
and humans have __ pairs

4. Chromosomes (X’somes)
chromosomes come in pairs
and humans have 23 pairs
this means humans have ___ total chromosomes

5. Chromosomes (X’somes)
chromosomes come in pairs
and humans have 23 pairs
this means humans have 46 total chromosomes

6. Karyotype
all of an organism’s chromosomes, photographed, cut out, and arranged by homologous pairs

7. Human Karyotype 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
XX (or XY)

8. Autosome
chromosomes that do not genetically determine gender

9. Human Karyotype 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
XX (or XY)

10. Sex Chromosome
chromosomes that genetically determine gender
X and Y

11. Human Karyotype 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
XX (or XY)

12. Alleles different versions of the same type of gene
Ex: blue eye color vs. brown eye color

13. Homologous Chromosomes
pairs of chromosomes that have the same structure and pair during meiosis

14. Homologous Chromosomes
can carry different alleles
cells have two of each chromosome
one chromosome in each pair from the mother (maternal), the other from the father (paternal)
paternal and maternal chromosomes carry different alleles

15. Meiosis
the process by which gametes (sex cells) are produced from a parent cell

16. Many plants produce gametes (sex cells) also!
Prentice-Hall Biology
Fig. 10-3
p.156

17. Meiosis & Chromosome Number
meiosis halves chromosome number

18. Meiosis & Chromosome Number
body (somatic) cells are diploid (2n)
have two sets of chromosomes (one maternal and one paternal)
n = number of chromosomes in one set = number of chromosomes received from each parent
in humans, n = 23

19. Meiosis & Chromosome Number
reproductive cells (gametes) are haploid (n)
have only one set of chromosomes (half the diploid number)
gametes = sperm & egg

20. Meiosis & Chromosome Number
two consecutive nuclear divisions resulting in four haploid cells
Meiosis I and Meiosis II

21. Discuss the four questions on the left side of your Cornell notes with your table partner.

22. 1. ) Compare & contrast diploid cells (2n) vs. haploid cells (n). 2
1.) Compare & contrast diploid cells (2n) vs. haploid cells (n). 2.) How many divisions occur in meiosis? 3.) How many cells are made? 4.) Are the cells made in meiosis haploid or diploid?

23. Meiosis I
Holt Biology p. 144

24. Meiosis I chromosome number is halved homologous pairs are separated
Each homologue in the
cell pairs with its partner,
then the partners
separate
Prentice Hall Biology, p. 158

25. Meiosis I and Crossing Over
Holt Biology p. 144

26. Crossing Over
each chromosome becomes attached to its homologue (partner)
all four chromatids are closely aligned
nonsister chromatids exchange segments

27. Effect of Crossing Over
after crossing over, each chromosome contains both maternal and paternal segments
this creates new allele combinations in offspring

28. Independent Assortment
random distribution of homologous chromosomes

29. Meiosis 1 and Independent Assortment

30. Effect of Independent Assortment
increases the number of possible different genetic combinations in gametes

31. Meiosis II
the two sister chromatids of each duplicated chromosome are separated from each other
two chromosomes
(unduplicated)
one chromosome
(duplicated)
p. 158

32. Meiosis II
Holt Biology p. 145

33. Meiosis Animation

34. Mitosis Graphic Organizer

35. Mitosis Graphic Organizer

36. Meiosis Graphic Organizer

37. Meiosis Graphic Organizer

38. Meiosis Graphic Organizer

39. Meiosis Graphic Organizer

40. Random Fertilization
remember, meiosis produces gametes, a.k.a. sex cells
sex cells combine randomly during fertilization to produce a new organism
because fertilization of an egg by a sperm is random, this also increases the number of possible genetic combinations

41. Evolutionary Change
crossing over, independent assortment, and random fertilization all increase the number of possible genetic variations
more genetic combinations = more possibilities for organisms to evolve

42. Errors in Meiosis
sometimes a gamete can be produced with an incorrect number of chromosomes because of non-disjunction
non-disjunction – failure of chromosomes to separate during anaphase I or II of meiosis

43. Meiosis and Non-disjunction
Normal meiosis(A)
Failure of homologous chromosomes to separate in anaphase I of meiosis I (B)
Failure of sister chromatids to separate in anaphase II of meiosis II (C) A B C

44. Meiosis and Nondisjunction

45. Meiosis and Nondisjunction

46. Errors in Meiosis
sometimes a gamete can be produced with an incorrect number of chromosomes because of non-disjunction
non-disjunction – failure of chromosomes to separate during anaphase I or II of meiosis
creates gametes with an extra or missing chromosome

47. Other Resources
Textbook pages