1. Cell Division: Mitosis & Meiosis

2. Chromosomes in us Humans have diploid cells
Diploid (2n) = two sets of each chromosome (2n = 46, where n is 23)
Haploid (n) = one set of each chromosome
Arranged in pairs known as homologous chromosomes = chromosomes pairs that are of the same length and staining pattern and possess genes for the same characters at the same length

3. Terms – refresher Chromatid = one of two copies of DNA
Sister chromatids = two identical copies of DNA
Centromere = region on chromosome that joins sister chromatids
Spindle fiber = microtubules that move chromosomes during cell division
Centriole = microtubule organizing center

4. Stages of the cell cycle
interphase
G1: growth, protein synthesis, increase in the number of mitochondria and/or chloroplasts
S: DNA replication
G2: growth, protein synthesis, preparation for mitosis/cytokinesis
mitosis = nuclear division
prophase
metaphase
anaphase
telophase
cytokinesis = cellular division

5. Prophase
Chromosomes condense by supercoiling, becoming visible to microscopic view
Centrioles move to opposite poles
Nucleolus disappears
Nuclear membrane disappears
Microtubular spindle apparatus forms at each pole

6. Metaphase Spindle microtubules attach to chromosome centromeres
Chromosomes move to the equator

7. Anaphase
Centromeres split as spindle microtubules pull chromatids to opposite poles (after centromeres split, sister chromatids are known as sister chromosomes)
Sister chromosomes move to opposite poles as microtubules shorten

8. Telophase Sister chromosomes have arrived at poles Spindle disappears
Centrioles replicate
Nuclear membrane reforms and becomes visible
Nucleolus becomes visible
Chromosomes decondense, becoming chromatin

9. Cell Division: Mitosis & Meiosis

10. Signs of down syndrome
Multiple developmental and health effects including:
Short stature, distinct facial features.
Mild to moderate physical and cognitive impairment.
Increased risk of problems involving heart, respiratory, digestive, hearing, vision, and/or thyroid glands.
Trisomy 21 (95% of all cases): three complete copies in all cells.
Mosaicism (1-2% of cases): three copies in some but not all cells.

11. Karyotype
Organization of chromosomes of a cell according to size and structure
Each human cell has 23 pairs of chromosomes
(22 pairs of autosomes, 1 pair of sex chromosome)
Can detect gene mutations = change in base sequence of a gene
Autosome = chromosome not involved in determining sex

12. Which is male and which is a female karyotype?

13. What is different about
this karyotype?

14. Down syndrome
A chromosomal disorder resulting from a partial or complete extra copy of chromosome 21.

15. The paradox
Human beings have 46 chromosomes in each cell. Your mom has 46 chromosomes in each cell. Your dad has 46 chromosomes in each cell. But you do not have 92 chromosomes in your cell. WHY?

16. 4.2.3 Meiosis: Reduction division from diploid to haploid cells
Paring of homologous chromosomes
Two divisions
Meiosis I: homologous chromosomes split
Meiosis II: sister chromatids split
3. Product: Four haploid (n) cells

17. Meiosis VS Mitosis

18. Meiosis I Prophase I: Metaphase I: Anaphase I: Telophase I:
chromosomes condense
spindle forms
pairing of homologous chromosomes
Metaphase I:
homologous chromosomes line up at equator
Anaphase I:
Spindle attach to chromosomes and pull homologous chromosomes to separate poles
Telophase I:
Chromosomes arrive at opposite poles of cell
Spindle disappears
Q. Is the cell a diploid/haploid at this stage?

19. Meiosis II Prophase II: Metaphase I: Anaphase I: Telophase I:
chromosomes condense
spindle forms
Metaphase I:
individual chromosomes line up at equator
Anaphase I:
Spindle attach to chromatids and pull sister chromatids to separate poles
Telophase I:
Chromatids arrive at opposite poles of cell
Spindle disappears

20. Mitosis versus Meiosis
Purpose of mitosis = growth, tissue repair, asexual reproduction

21. Down syndrome Chromosomes move to pole as a pair instead of singly
Thus, egg or sperm contain an extra copy of chromosome 21, and fertilized egg has 3 copies of chromosome 21
Occurs in meisos I or II