1. Phases of Meiosis

2. Figure Meiosis
Section 11-4
Meiosis I

3. Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.
The chromosomes line up in a similar way to the metaphase stage of mitosis.
The sister chromatids separate and move toward opposite ends of the cell.
Meiosis II results in four haploid (N) daughter cells.

4. 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

5. 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

6. MITOSIS vs MEIOSIS METAPHASE METAPHASE I
Chromosomes line up in middle
Chromosomes line up in middle
with homologous partner

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

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

9. MITOSIS vs MEIOSIS CYTOKINESIS CYTOKINESIS I
Cytoplasm splits
into 2 cells
SAME AS
MITOSIS

10. 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

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

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

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

14. MITOSIS vs MEIOSIS TELOPHASE TELOPHASE II
Two nuclei
Nuclear membrane/ nucleolus returns
Centrioles/spindle fibers disappear
DNA spreads out as
chromatin
SAME AS MITOSIS

15. MITOSIS vs MEIOSIS CYTOKINESIS CYTOKINESIS II
SAME AS MITOSIS
Cytoplasm splits

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

17. Nondisjunction –
Failure of homologous chromosomes OR chromatids to separate at anaphase

18. Mistakes in Meiosis
Meiosis Lecture 4

19. Nondisjunction
Results in ANEUPLOIDY = one or more chromosomes have extra or missing copies
AFTER FERTILIZATION: Cell with only 1 copy of a chromosome instead of 2
= MONOSOMY
Cell with 3 copies of a
chromosome instead of 2
= TRISOMY

20. Errors in mitosis or meiosis can result in changes in phenotype
Changes in chromosome number often result in:
New phenotypes
Sterility caused by triploidy and increased vigor of other polyploids
human disorders with developmental limitations
Trisomy 21 (Down syndrome)
XO (Turner Syndrome)

21. Karyotype can show: Sex of baby Missing or extra chromosomes
Major deletions or translocations
Can’t see individual gene changes

22. Down syndrome (Trisomy 21)
Most common chromosomal abnormality (1 in 800 births)
Similar facial features Slanted eyes / Protruding tongue Mild to severe mental retardation
50% have heart defects that need surgery to repair
Both older (35+ years) and younger (under 16 years) mothers are more at risk.

23. Some individuals with Down syndrome have the normal number of chromosomes but have all or part of a third chromosome 21 attached to another chromosome by translocation.

24. Turner syndrome (X0)
1 in 5000 births
Females have only one X chromosome
Small size
Broad chest
Slightly decreased intelligence
35% have heart abnormalities
Hearing loss common
Reproductive organs don’t develop at puberty

25. http://www. akdeniz. edu
Klinefelter syndrome
1 in 2000 births live births
Males have extra X chromosomes
(Can be XXy, XXXy, or XXXXy)
Taller than average
Normal intelligence have male sex organs, but are sterile. may be feminine characteristics,
Often not discovered until puberty when don’t mature like peers
Presence of BARR BODIES