1. Submit your karyotype activity sheet. Feedback distributer: Sabrina
4.2 Meiosis
Submit your karyotype activity sheet.
Feedback distributer: Sabrina

2. 4.2.6 Methods of karyotyping: Amniocentesis
Insert a needle into uterus and extract 10 mL of amniotic fluid (liquid that bathes the fetus)
Biochemical test of the fluid to identify certain chromosomal defects
Some tests require that cells be cultured (several weeks) before they can be tested
Performed 14th – 16th week of pregnancy

3. 4.2.6 Methods of karyotyping: Choronic villus sampling (CBS)
Chorionic villi = Microscopic, finger-like projections which surrounds developing baby. Eventually forms placenta
Insert narrow tube through the cervix into the uterus and take out fetal tissue
Cells of chorionic villus are rapidly multiplying, therefore tests can be carried out immediately (give results in less than 24 hours)
Performed as early as 8th – 10th week of pregnancy

4. 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

5. 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

6. 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?

7. 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

8. 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?

9. 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

10. Meiosis versus Mitosis

11. Feedback distributer: Sabrina
4.2 Meiosis
Feedback distributer: Sabrina

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

13. Crossing over: Prophase I
Non-sister chromatid from each homologous pair intertwine, reciprocal exchange genetic info

14. Significance: produce 4 haploid cells, each with new combination of alleles! (i.e. increases genetic variation)
We didn’t do this with our activity – 4 stacks (2 different combinations)

15. 4.2.4 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