1. Bio NOTES: Chromosomes and Meiosis
There are two types of chromosomes found in cells:
- autosomes
- sex chromosomes
Your body cells have 23 pairs of
chromosomes
- homologous pairs of chromosomes
have the same structure
- for each homologous pair,
one chromosome comes from
each parent
Chromosome pairs 1-22 are autosomes.
Sex chromosomes, X and Y, determine
gender in mammals.
XX =
XY =
female
male

2. HOMOLOGOUS CHROMOSOMES
SAME SIZE
SAME SHAPE
CARRY GENES for the SAME TRAITS
BUT ______________!
(Don’t have to have the SAME CHOICES)
Image modified by Riedell
NOT IDENTICAL

4. Body Cells
- also called somatic cells
- body cells are diploid
Diploid (2n) cells – have two copies
of every chromosome
- half the chromosomes come from each parent
Gametes
- also known as sex cells
(sperm and egg)
- gametes have DNA that can be
passed to offspring
- gametes are haploid
Haploid (n) cells – have one copy of each chromosome
- gametes have 22 autosomes and 1 sex chromosome

5. Key Terms Diploid refers to complete chromosome sets in a cell (or 2N)
N= the number of chromosomes in a gamete (sex cell)
N chromosomes from the female parent + N chromosomes from the male parent= 2N
For humans, 2N = 46
Nothing to write on FIB

6. Key Terms Haploid refers to single chromosomes in a cell (or N)
One-half of the 2N set (the maternal N or the paternal N)
Gametes (i.e. sperm, egg sex cells) are haploid cells
For humans, N = 23

7. diploid means there are the full number of chromosomes in cells
Bottom Line
diploid means there are the full number of chromosomes in cells
haploid means that there are half the number of chromosomes in cells

8. Mitosis and meiosis are types of nuclear division that
make different types of cells.
Meiosis
- occurs in sex cells (gametes)
makes 4 haploid cells
produces gametes that are genetically Unique
Mitosis
- occurs in somatic cells
makes 2 diploid cells
Produces somatic cells that are genetically Identical

9. MEIOSIS 10-1 Making gametes…
Making gametes…

10. + EGG SPERM  If egg and sperm had same number of
Image by Riedell
Image by Riedell
EGG +
SPERM 
If egg and sperm had same number of
chromosomes as other body cells . . .
baby would have too many chromosomes!

11. MEIOSIS is the way… to make cells with ½ the number of chromosomes
for sexual
reproduction

12. Meiosis reduces the chromosome number and creates genetic diversity.
Cells go through two rounds of division in meiosis:
Meiosis I and meiosis II each have four phases, similar to
those in mitosis
During meiosis I – pairs of homologous chromosomes separate
- homologous chromosomes are similar, but not identical
During meiosis II – sister chromatids divide
- sister chromatids are copies of the same chromosome
homologous chromosomes
sister
chromatids

13. Meiosis I
Meiosis I occurs after DNA has been replicated in interphase
Meiosis I divides homologous chromosomes in four phases:
prophase I  metaphase I  anaphase I  telophase I
After cytokinesis, two cells are produced with one homologous
chromosome each

14. Meiosis II
DNA is not replicated between meiois I and meiosis II
Meiosis II divides sister chromatids in four phases:
prophase II  metaphase II  anaphase II  telophase II
After cytokinesis, four new cells are produced, each with half
the chromosome number (haploid)

15. Stop here day 1 Option 1 Work on Vocab List Option 2
Complete Web quest

16. MITOSIS vs MEIOSIS INTERPHASE INTERPHASE I
DNA is spread out as chromatin
Nuclear membrane/ nucleolus visible
DNA is copied during S phase
Makes stuff new cell needs in G2
SAME AS
MITOSIS

17. MITOSIS vs MEIOSIS PROPHASE PROPHASE I
DNA scrunches into chromosomes Nuclear membrane/ nucleolus disappear Centrioles/spindle fibers appear
DNA scrunches into chromosomes
Nuclear membrane/ nucleolus disappear
Centrioles/spindle fibers appear
Homologous pairs match up
CROSSING OVER OCCURS!

18. WHAT MAKES MEIOSIS DIFFERENT?
1. Exchange of DNA between homologous pairs = _____________ during PROPHASE I
CROSSING OVER
Allows shuffling of genetic material

19. Click the image to play the video segment. 11E
Crossing Over
SEE CROSSING OVER ANIMATION
Click the image to play the video segment. 11E
Video 5

20. rearranging of DNA NOT IDENTICAL CROSSING OVER
Image modified by Riedell
CROSSING OVER
rearranging of DNA
Allows for_________________
in different combinations
After crossing over, chromatid arms are________________ anymore
NOT IDENTICAL

21. MITOSIS vs MEIOSIS METAPHASE METAPHASE I
Chromosomes line up in middle
HOMOLOGOUS Chromosomes line up in middle .
Independent assortment occurs

22. METAPHASE I Spindle fibers attach to the centromeres
Homologous Chromosomes Line up at the equator
chromosome pairs line up randomly in cell

23. Click the image to play the video segment 11D.
Segregation of Chromosomes
Click the image to play the video segment 11D.
Video 4

24. MITOSIS vs MEIOSIS ANAPHASE ANAPHASE I
APART:
APART:
Chromatids split
Chromatids stay together Homologous pairs split

25. MITOSIS vs MEIOSIS TELOPHASE TELOPHASE I
See TWO nuclei
Nuclear membrane/
nucleolus return
DNA spreads out as chromatin
Spindle/centrioles disappear
SAME

26. MITOSIS vs MEIOSIS CYTOKINESIS CYTOKINESIS I
Cytoplasm splits
into 2 cells
SAME AS
MITOSIS
2 Genetically Different Haploid Cells Form

27. MITOSIS vs MEIOSIS INTERPHASE II
DNA is spread out as chromatin
Nuclear membrane/ nucleolus visible
DNA is copied during S phase
SKIP
INTERPHASE II
DNA NOT COPIED

28. MITOSIS vs MEIOSIS PROPHASE PROPHASE II
DNA scrunches into chromosomes
Nuclear membrane/ nucleolus disappear
Centrioles/ spindle fibers appear
SAME AS MITOSIS

29. MITOSIS vs MEIOSIS METAPHASE METAPHASE II
Chromosomes line up in middle
SAME AS MITOSIS

30. MITOSIS vs MEIOSIS ANAPHASE ANAPHASE II
Sister Chromatids split and move apart
SAME AS MITOSIS

31. MITOSIS vs MEIOSIS TELOPHASE TELOPHASE II
Two nuclei
Nuclear membrane/ nucleolus returns
Centrioles/spindle fibers disappear
DNA spreads out as
chromatin
Same as Mitosis

32. MITOSIS vs MEIOSIS CYTOKINESIS CYTOKINESIS II
SAME AS MITOSIS
4 haploid Genetically unique Cells
Cytoplasm splits
2 diploid Genetically Identical cells

33. Stop Here day 2
Complete Vocab and SG sheet due by end of class.

34. Ways Meiosis is different?
Homologous pairs match up & trade DNA (&CROSSING OVER) in PROPHASE I
INDEPENDENT ASSORTMENT in metaphase I
creates genetic recombination
Skipping INTERPHASE II-
(Dividing TWICE but copying DNA once)
produces 1n cells

35. Sources of Variations and Differences
Crossing over
occurs during prophase I
homologous chromosomes swap pieces
this chromosome swapping creates variations
Random assortment of chromosomes
chromosome pairs line up randomly in cell
when the pairs separate, this creates cells with
genetic variations
Fertilization
which
sperm gets
to the egg first??
it is random and can
create variations in
offspring