this is part of abundle

1. Meiosis
 What is meiosis?
 Gametes
 Chromosomes
 Diploid vs. haploid
 Meiosis I
– Recombination
 Meiosis II

2. What is Meiosis?
 From a Greek word meaning “lessening”
 Occurs in sexually-reproducing
eukaryotes
– Eukaryotic cells have nucleus, cell
membrane, and chromosomes
 __________

3. What is Meiosis?
 Gametes are produced in
animals
 Spores are produced in
plants and some algae
 _____________

4. Gametes
 Gametes are sex cells: eggs and sperm
 In sexual reproduction, they combine to
form a zygote (precursor to an individual
offspring)

5. Chromosomes
 DNA molecules
 Carry genetic
information coding
for an organism

6. Chromosomes
 ___________
– 22 pairs are autosomes (not sex
chromosomes)
– One pair is the sex chromosomes (X and Y)
 Males: XY
 Females: XX

7. Diploid vs. Haploid
 Diploid: cells with paired chromosomes
(46 total)
 ____________

8. Diploid vs. Haploid
 Gametes are haploid
 When they combine, they create a
diploid zygote

9. Meiosis
 Initial phase
– Interphase
 Two cell divisions
– Meiosis I
– Meiosis II

10. Interphase
 DNA in dividing cell nucleus is copied
– ___________

11. Interphase
Centrosomes outside nucleus are duplicated
 Centrosomes contain centrioles in animals
 Microtubules branch out from centrosomes
 ____________

12. Meiosis I
 Four phases
– Prophase I
– Metaphase I
– _________
– _________

13. Prophase I
 Chromosomes become condensed
(shorter, thicker, and coiled) and visible
with a microscope
– Chromosomes made up of sister chromatids
joined in an X shape
– ___________

14. Prophase I
 Homologous chromosomes
(copies of the same gene from
mother and father) pair, forming
a tetrad (four chromosomes)
 ________
– Results in further genetic diversity

15. Recombination
 Within the tetrad, the arms of the
chromosomes may overlap
– Overlapping points are called chiasmata
 At chiasmata, sections of DNA may be
broken and recombined with overlapping
sections of another chromosome
Chiasma

16. Recombination
 This results in new gene combinations
 ____________

17. Prophase I
 __________
– _________
 Meiotic spindle forms
– Made of microtubules and proteins
– Connects centrioles at opposite poles of
cell
 Nuclear envelope disappears

18. Metaphase I
 Homologous
chromosome pairs line
up at center of cell
– Metaphase plate
 Meiotic spindle fibers
attach chromosomes
– _________

19. Anaphase I
 Two chromosomes of each tetrad are
pulled to opposite poles of cell by
spindle
 _________

20. Telophase I
 Chromosome pair at the poles
– Haploid set at each pole
 Nuclear envelope forms around each
set
 Meiotic spindle disappears

21. Cytokinesis
 In animal cells:
– Cleavage furrow formed
– Cell is pinched into two cells
– Each new cell has haploid set of
chromosomes

22. Meiosis II
 Four phases
– Prophase II
– Metaphase II
– Anaphase II
– Telophase II and cytokinesis
 ____________

23. Prophase II
 Centrioles duplicate
– Pair of centrioles separates
– Daughter centriole forms perpendicular to
each single centriole
– _________
Daughter centrioles

24. Prophase II
 Nuclear envelope disappears
 ____________
Spindle Fibers

25. Metaphase II
 ____________
 Microtubules from each pole attach to
centromeres of chromosomes
– Kinetochores (proteins in each sister chromatid
that make up centromeres) face opposite poles
– Microtubules attach to kinetochores

26. Anaphase II
 ____________
 Chromatids pulled to opposite poles
 Separated chromatids now considered
chromosomes

27. Telophase II & Cytokinesis
 Nuclear envelope forms around each
set of chromosomes
 ____________
 Four daughter cells are produced