1. Bellringer 11/15/12
1. What are the steps of the cell cycle ALL 6 IN ORDER ?
retrieve a note sheet from the front cart. Glue it to page 47 (45-honors).

2. Meiosis Definition: Cell division of gametes (sex cells—eggs & sperm)
Purpose: To make genetically different reproductive sex cells.
Cells contain ½ the normal amount of chromosomes. (haploid)
Zygote: A fertilized cell (egg + sperm together)

3. What is Produced by Meiosis?
Four haploid cells (1n)
Each cell is genetically different!

4. Diploid Cells Two sets of chromosomes in a cell.
½ from mom, ½ from dad. 2n
All body cells are diploid
Made by mitosis

5. Haploid Cells One set of chromosomes in a cell. 1n
All sex cells are haploid
Made by meiosis

6. What is different about meiosis?
Many different variations in the gametes because of crossing over. Crossing over is when tetrads bind tightly, parts break off and are swapped between the chromatids
Sex cells divides twice, but only copies DNA once.
Tetrad: when 2 homologous chromosomes bind together during prophase I of meiosis.

7. Before Meiosis Homologous chromosomes are attached to each other
Homologous chromosomes: Two of the same type of chromosome
Chromosomes copy themselves so that they can be passed along to the daughter cells

8. Before Meiosis
Tetrad: 2 homologous chromosomes attached together (= 4 sister chromatids)

9. Comparing Mitosis and Meiosis
DNA replicates in interphase
ONE division of chromosomes
Separate sister chromatids
TWO divisions of chromosomes
Separate homologous chromosomes (meiosis I)
Separate sister chromatids (meiosis II)
Makes 2 identical DIPLOID cells
Makes 4 HAPLOID cells
Chromosome # is identical to parent cell
Chromosome # is HALF of the parent cell
Used for replacement, repair, & growth
Used to make gametes

10. Mistakes in Meiosis
Nondisjunction: when homologous chromosomes fail to separate from each other during meiosis (either Anaphase I or II)
Result: Gamete(s) may have too many chromosomes, while other gamete(s) are missing that chromosome

11. Mistakes in Meiosis
Organisms with extra chromosomes can survive; organisms with too few usually do not survive
Polyploidy: when organisms have more than the normal number of chromosome sets
Can be lethal for animals but not plants (plants just usually get bigger)..Remember, we used strawberries for DNA extraction because they’re octoploids

12. Nondisjunction in Sex Chromosomes
Turner’s Syndrome (Female)
Genotype: X
can cause a variety of medical
and developmental problems, including short stature, failure to begin puberty, infertility, heart defects and certain learning disabilities

13. Trisomy X (Females) Genotype: XXX
may be taller than average, but this chromosomal change typically causes no unusual physical features.
most females with triple X syndrome have normal sexual development and are able to conceive children
Triple X syndrome is associated with an increased risk of learning disabilities and delayed development of speech and language skills

14. Klinefelter’s Syndrome
Males-XXY
MOST COMMON
male sex organs; unusually small testes, sterile
breast enlargement and other feminine body characteristics
normal intelligence

15. Jacob’s Syndrome Males-XYY hard to determine
individuals are somewhat taller than average and often have below normal intelligence
at one time (~1970s), it was thought that these men were likely to be criminally aggressive, but this hypothesis has been disproven over time.

16. Nondisjunction in Autosomes
Patau’s Syndrome
Trisomy 13
serious eye, brain,
circulatory defects,
cleft palate, polydactly
1:5000 live births
Children rarely live more than a few months.

17. Down Syndrome Trisomy 21 characteristic facial features,
short stature; heart defects
susceptibility to respiratory disease, shorter lifespan
prone to developing early Alzheimer's and leukemia
often sexually underdeveloped and sterile, usually some degree of mental retardation.

18. Edward’s Syndrome Trisomy 18 About 95% die before birth
Of liveborn infants, only 50% live to 2 months, and only 5–10% will survive their first year of life
almost every organ system affected 1:10,000 live births

19. Meiosis I: Separating the Homologues
Prophase I
Chromosomes appear
Crossing-over occurs between chromosomes (now tetrads)
Nuclear membrane disappears
Metaphase I
Tetrads line up at the equator (middle)

20. Meiosis I: Separating the Homologues
Anaphase I
Tetrads separate and move to opposite ends of the cell
Telophase I/Cytokinesis
Cytoplasm divides & 2 daughter cells are formed
Each cell has a homologous chromosome

21. Meiosis II: Separating the Sister Chromatids
Prophase II
Nuclear membrane disappears
Metaphase II
Chromosomes line up along equator (not in homologous pairs)

22. Meiosis II: Separating the Sister Chromatids
Anaphase II
Sister chromatids separate and move to opposite ends of the cell
Telophase II/Cytokinesis
Cytoplasm divides
New membranes are formed
4 HAPLOID daughter cells formed
Each contains ONE chromosome from each homologous pair

23. Chromosomal Structural Mutations
1. Deletion: a part of one chromosome is lost during cell division so its now missing certain genes
Example-- Cri du chat (cry of the cat):
a specific deletion of a small portion of chromosome 5
these children have severe mental retardation, a small head with unusual facial features, and a cry that sounds like a distressed cat

24. Example--Fragile X: the most common form of mental retardation
2. Duplication: a part breaks off of a chromosome and joins the other homologous chromosome, so that region is repeated
Example--Fragile X: the most common form of mental retardation
Fragile X have over 700 repeats due to duplications
Affects 1:1500 males, 1:2500 females

25. 3. Translocation: a fragment of a chromosome is moved from one chromosome to another
Example-- Acute myelogenous leukemia (AML) is a fast-growing cancer of the blood and bone marrow
white blood cells (WBC) do not develop and cannot fight infections
Bone marrow may also
make abnormal red blood
cells and platelets

26. Karyotypes
Karyotypes: a picture of the complete number and appearance of chromosomes in a person
Autosomes: a non-sex chromosome or chromosome pairs 1-22
Sex chromosomes: chromosome pair 23 which determine the sex/gender of a person