1. 2n 2n egg (n) sperm (n) fertilization zygote Egg cell Sperm cell MEIOSIS MEIOSIS MITOSIS You MEIOSIS … making gametes….

2. Each of your body cells has 2 sets of chromosomes – one from mum, one from dad. Any cell that has 2 complete sets of chromosomes is said to be DIPLOID OR 2n When 2 cells come together in fertilization to make a zygote, each can only have 1 set of chromosomes. These cells ( = egg/sperm, gametes) are said to be MONOPLOID or n.

3. Why do meiosis? Meiosis is “ REDUCTION DIVISION”. Reduces chromosome number, parent cell is 2n while daughter cells are n. Why do ovary and testes cells go through meiosis?

4. CHROMOSOME NUMBER In humans, 2n=46 This means we’re referring to a normal body cell that has a total of 46 chromosomes, but they are of 2 sets - 23 from mom, 23 from dad) In humans, n = 23 This means we’re talking about a cell that has only half the normal chromosome number (n) and that is only one set. This cell must therefore be a gamete.

6. Homologous pairs. In each body cell you have 23 homologous pairs. 2 chromosomes are homologous if: - one is from mum, one is from dad - they have the same types of genes on them (eg. Circled chromosomes may contain genes for blood type hair colour etc.)

7. The chromosomes on the previous page are homologous because they have the same gene sequence. You can tell which chromosomes are homologous as they have: 1. the same type of genes. 2. The same banding pattern 3. The same position of the centromere.

12. Products of MITOSIS: 2 x 2n cells. 2 diploid cells Products of MEIOSIS: 4 x n cells (4 monoploid cells) 2n 2n 2n 2n n n n n

13. MEIOSIS is two mitotic divisions in a row, (meiosis I and II) except you will see the homologous chromosomes coming together . - -- in prophase I the double homologous chromosomes come together to form a tetrad - Crossing-over (synapsis ) occurs in the tetrad in prophase to increase the variability in gametes. - There is no dna replication in the interphase between the first and second divisions

19. Prophase I - Synapsis From Mum From Dad Homologous chromosomes sister chromatids sister chromatids Tetrad

21. Homologous Chromosomes eye color locus eye color locus hair color locus hair color locus Paternal Maternal

23. Crossing Over - variation variation nonsister chromatids chiasmata: site of crossing over Tetrad

24. Sex Chromosomes XX chromosome - female XY chromosome - male

25. Prophase I centrioles spindle fiber aster fibers

27. Metaphase I metaphase plate OR metaphase plate

29. Anaphase I

31. Telophase I

33. MEIOSIS II

38. Telophase II

39. Cytokinesis: cytoplasm divides. Total product is 4 cells, each with only a mom or Dad’s chromosome , in other words, half the normal chromosome number , or 4 monoploid (n) cells, or 4 gametes. Uneven cytokinesis in females: In oogenesis, get one big egg and 3 non-functional polar bodies: ( who die off) and 1 big functional gamete

40. First division: results in one big primary oocyte and a little polar body. Second division: One secondary oocyte and 3 polar bodies. ( These polar bodies die.) OOGENESIS Oocyte Polar Bodies Oogonium Primary Oocyte Mitosis Polar Body Secondary Oocyte Meiosis I Meiosis II

42. Spermatogenesis There are equal divisions producing four equal sized sperm .

44. Compared to the number of chromosomes contained in a body cell of a parent, how many chromosomes would normally be contained in a gamete? F. the same number G. twice as many H. one-fourth as many J. half as many During mitosis, the chromosomes A. are located at the cell equator during prophase B. are located at the cell equator during telophase C. move toward the poles of the cell during anaphase D. move toward the poles of the cell during metaphase Some questions on mitosis and meiosis!

45. 1. Meiosis occurs in this life cycle when A. an egg and a sperm fuse to form a zygote B. a mature polyp produces a medusa C. a planula produces a young polyp D. a medusa produces gametes . Which structures normally have a haploid number of chromosomes? A. Seed plant spores and animal zygotes B. Seed plant spores and animal gametes C. Seed plant zygotes and animal zygotes D. Seed plant gametes and animal zygotes

46. Processes II and IV illustrate budding. The information in the diagram indicates that budding is a type of A. asexual reproduction that produces haploid or diploid cells B. asexual reproduction that produces diploid cells C. sexual reproduction that produces haploid or diploid cells D. sexual reproduction that produces haploid cells

47. = Non-separation of chromosomes resulting in diploid or empty gametes. Non-disjunction

48. Downs syndrome = Trisomy 21 - 3 copies of chromosomes 21 equalling a total of 47 chromosomes. = 2n + 1(chance of occurring in oogenesis increases with maternal age) Turners syndrome = Monosomy X - has only one X chromosomes totalling only 45 chromosomes in her body cells. (monosomy X) = 2n-1 Klinefelter’s syndrome = XXY - male which has an extra X chromosome = 2n + 1 Conditions caused by non-disjunction

49. A simple check for the presence of a bone in the nose could more accurately test unborn babies for Down's syndrome, scientists say. Researchers say combining the nose test with existing screening methods (amniocentesis, CVS) could lead to a five-fold reduction in the number of miscarriages linked to an invasive procedure used to confirm Down's syndrome. Down’s syndrome – trisomy 21

50. Normal boy who develops some female secondary sex character-istics at puberty. -slightly lower IQ, infertile, delayed motor, speech, maturation -treated with testosterone. Klinefelter’s syndrome XXY