1. Meiosis with Mitosis Review and Comparison (Chapters 8 and 10)

2. Recall Mitosis
** Mitosis is asexual reproduction & occurs ONLY in regular old body cells called SOMATIC CELLS (skin, nails, your pancreas, etc..) NOT sperm and eggs 
** Produces two identical diploid (2n) cells

3. Diploid Chromosomes
We call somatic cells diploid (2n) meaning you have 2 copies of each chromosome (1/2 from mom and ½ from dad)
Autosomal chromosomes are non-sex chromosomes
These contain genes that have nothing to do with determining your sex
Each of your cells contain 44 autosomal chromosomes and 2 sex chromosomes (XX for female and XY for male) for a total of 46 chromosomes in each nuclei of your cells

4. Cell Cycle – Diploid (2n), Somatic Cells (Body Cells)

5. Mitosis Produces Identical, Diploid Daughter Cells (46 chromosomes in the nuclei of the cells)
Replicates
Above are Homologous Chromosomes - Same chromosome with same types of genes on each chromosome, just different variations from each parent

6. Meiosis and The Human Life Cycle
FROM MOM
FROM DAD

7. Meiosis Overview **Required for Sexual Reproduction
**Diploid cells divide twice to produce haploid (n) sperm or egg (each have 23 chromosomes)
**Produced in the ovaries (females) and testes (male)
**Results in 4 NON-IDENTICAL haploid (n) cells
Genetic recombination creates genetic variability in either sperm or egg
For each meiotic division, 4 sperm are produced but typically only 1 egg survives

8. Meiosis Phases **After interphase (DNA replication phase)
**Meiosis I  Prophase I, Metaphase I, Anaphase I, telophase I
**Meiosis II  Prophase II, Metaphase II, Anaphase II, Telophase II and cytokinesis
**4 cells, the gametes!!

9. Fertilization
When egg and sperm fuse we say the egg is fertilized creating one, single diploid cell called a zygote
Although numerous sperm attempt to fertilize the egg, only one will succeed
Diploid zygote – will undergo mitosis

10. Sex Chromosomes
Male = XY
Female = XX

11. Meiosis occurs in 2 phases
Meiosis occurs in 2 phases. Meiosis 1 and Meiosis 2 with cytokinesis following. The process results in 4 non-identical haploid cells
After Meiosis 2 occurs the result is 4, non-identical haploid sperm or egg cells called gametes
After Meiosis 1
From your From your
Dad Mom
Replication
Homologous chromosomes – SAME chromosome type (have the same types of genes)
A tetrad is formed
Crossing Over between non-sister chromatids During Prophase 1 of Meiosis 1 – Results in genetic recombination

12. Meiosis I

13. Meiosis II

14. Genetic Recombination

15. Genetic Recombination During Meiosis
** A reassortment of chromosomes and genetic information they carry
**crossing over between non-sister chromatids during Prophase 1
**independent assortment of homologous chromosomes

16. Crossing Over **Pink is from your mom, blue from your dad
**Non-sister chromatids exchange genetic information

17. Sister Chromatids of Homologous Chromosomes Cross Over

18. Independent Assortment leads to genetic variability- homologous chromosomes are sorted before shipment to gametes independently of how the other pairs were sorted

19. Meiosis Square Dance

20. Problems During Meiosis

21. Non-Disjunction
**chromosomes of a homologous pair (tetrad) fail to separate and move to the same pole of the cell. Some gametes may have an extra chromosome while others lacking
** Down syndrome occurs because of this. Called trisomy 21, there are 3 of chromosome #21 rather than a pair!

22. Karyotypes – Pictures of a person’s Chromosomes – Show Abnormalities
Male with no chromosomal abnormalities

23. Abnormal Karyotype
Trisomy 18 – Due to Non-disjunction

24. Compare Mitosis to Meiosis

25. Mitosis (asexual reproduction) vs. Meiosis (sexual Reproduction)
Occurs in 2 stages
Produces 4 genetically different haploid cells (genetic recombination)
For Sexual Reproduction
Produces genetically variability due to recombination
Occurs in sex cells called gametes or germ cells and four haploid cells (sperm and egg)
n=23  22 autosomal chromosomes and 1 sex chromosome
Forms a tetrad
Mitosis
Occurs in 1 stage
Produces 2 genetically identical diploid cells
It is Asexual Reproduction
Produces “clones” with no genetic variability
Occurs in body cells (autosomal) and creates two diploid cells
2n=46  22 pair of autosomal chromosomes and 1 pair sex chromosomes

26. Mitosis
Meiosis