1. Unit 4 – Growth & Reproduction
Meiosis
Unit 4 – Growth & Reproduction

2. Terms to Know – (add to vocab page)
Replicated Chromosome – a chromosome that has doubled it’s DNA
Non-Replicated Chromosome – a chromosome that has split and contains only one copy of DNA.
Homologous Chromosome –corresponding (matching) chromosomes from a female and male parent.
Diploid Cell (2n) – a cell that contains both sets of homologous chromosomes
Haploid Cell (n) – a cell that contains one set of homologous chromosomes
Gene – segment of DNA that codes for a trait

4. What is Meiosis and do we need it?
A form of cell division happening in sexually reproducing organisms consisting of two consecutive cell divisions (meiosis I and meiosis II).
Produces 4 sex cells
Men  4 sperm cells (in the testes)
Women  1 egg and 3 polar bodies (in the ovaries)

5. Meiosis Overview Meiosis I:
One diploid cell (46 replicated chromosomes/23 pairs) becomes two haplod cells (23 replicated chromosomes.) (start with 92 chromatids)
Meiosis II:
Two haploid cells (23 replicated chromosomes) becomes 4 haploid cells (23 non-replicated chromosomes.)

7. Why do we need Meiosis?
Distributes maternal and paternal chromosomes evenly and randomly (genetic variation).
Meiosis is necessary to half the number of chromosomes going into the sex cells.
Why half the chromosomes in gametes?
At fertilization the male and female sex cells will provide ½ of the chromosomes each – so the offspring has genes from both parents

8. Why do we need Meiosis? continued.23 46 23

10. Female vs. Male Oogenesis egg production Spermatogenesis
Sperm Production

11. What does Meiosis accomplish?
Meiosis takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid).
Meiosis scrambles the specific forms of each gene that each sex cell (egg or sperm) receives through crossing over and independent assortment.

12. Meiosis I – starts diploid Meiosis II – starts haploid
Steps in Meiosis
Same steps as Mitosis, divides twice to produce 4 daughter cells instead of 2.
Daughter cells are not identical but similar
Meiosis I – starts diploid
Meiosis II – starts haploid
PMAT
2 similar cells
23 chromosomes
Separates homologous pairs
Haploid
PMAT
4 similar cells
23 chromosomes
Separates replicated chromosomes
Haploid

17. Interphase/Prophase I
Cells duplicate their DNA
Prophase I
sister chromatids pair up forming a homologous chromosome
Crossing Over
When two chromosomes exchange portions of their chromatids
Occurs during

18. Metaphase I Metaphase I
Spindle fibers attach to the centromeres on each chromosome
Homologous chromosomes line up together.

19. Anaphase I
Anaphase I
Spindle fibers pull the homologous chromosomes toward opposite ends of the cell.

20. Telophase I/Cytokinesis
Meiosis I results in 2 haploid (n) daughter cells.
Each with half the number of chromosomes as the original cell (23)
Still replicated chromosomes.

21. Prophase II Prophase II
2 haploid (n) daughter cells. Each with half the number of chromosomes as the original cell.
Interphase does NOT happen again.
Same steps as normal prophase.

22. Metaphase II Metaphase II
The chromosomes line up in a similar way to the metaphase stage of mitosis. Occurs in BOTH cells.

23. Anaphase II Anaphase II
The sister chromatids separate and move toward opposite ends of the cell

24. Telophase II / Cytokinesis
Opposite of prophase occurs, cytoplasm splits.
END RESULT: four haploid (n), non-replicated, non-identical daughter cells.

25. Fertilization
The haploid sperm (carrying 1 set of chromosomes) combines with the haploid egg (carrying 1 set of chromosomes). The result is a diploid zygote.

26. Mitosis vs. Meiosis Diploid 2n  diploid 2n
46 chromosomes  46 chromosomes
Replicated chromosomes  Non-Replicated Chromosomes
Somatic Cells
Creates 2 identical cells
1 trip through PMAT
Dploid 2n  haploid n
46 chromosomes  23 chromosomes
Replicated chromosomes  non-replicated chromosomes
Gamete cells
Creates 4 similar cells
2 trips through PMAT

27. Meiosis Drawing Things to Label: pg. 276/277
Label Meiosis 1 and Meiosis 2
Label each cell as diploid (2n) or haploid (n)
Label the chromosome number of each cell
Circle and label a homologous pair of chromosomes
Circle and label a replicated chromosome.
Circle and label a non-replicated chromosome.
4 or 6 chromosome.

28. Meiosis Poster Label each cell as diploid (2n) or haploid (n)
Circle and label a homologous pair of chromosomes
Circle and label a replicated chromosome.
Circle and label a non-replicated chromosome.
Label a centromere
Label a pair of centrioles
Label a set of spindle fibers