1. Sexual Reproduction Vocabulary: Gamete Alleles Somatic Cells
Haploid Diversity Meiosis
Diploid Dominant Homologous
Fertilization Recessive Chromosomes
Aphids, slime molds,sea anemones, some species of starfish (by fragmentation), and many plants are examples.

2. Sexual Reproduction Key Ideas
CHAPTER
Sexual Reproduction Key Ideas 3
Meiosis is the process that produces sex cells.
Sexual reproduction involves the joining of genetic material from two parents.
Sexual reproduction creates the incredible diversity among members of the same species.
There are advantages and disadvantages to both asexual and sexual reproduction.
Organisms use a variety of strategies to ensure the success of sexual reproduction.
Scientists have used their knowledge of sexual and asexual reproduction to develop reproductive technologies.

3. Sexual Reproduction Summary
Requires TWO parents
Offspring are NOT identical to the parents
Requires the formation of specialized cells (gametes) which only function the process of meiosis.
One gamete from each parent combine to form a zygote through a process called fertilization.
Sperm cell reach a jelly-like coating surrounding the egg cell and release substances that digest a path through the coating. This helps sperm cells get closer to eth cell membrane fo the egg.
The head of one sperm cell eventually enters the egg cell, where the sperm nucleus fuses with teh egg nucleus.

4. Organisms that reproduce sexually produce 2 types of cells
Somatic Cells – body cells (skin, muscle, bone, etc)
Reproduce by cell division (mitosis)
Each cell contains a double set of chromosomes (diploid number = 2n)
Humans have 23 pairs of chromosomes (46 total)
Gamets - Sex cells
Sperm (male gametes)
Ova (female gametes)
Created by process called meiosis
Contain only a single set of chromosomes (haploid number = n)

5. Homologous Chromosomes
Each cell has two sets of chromosomes, one set from the mother, one set from the father. They are similar to each other (homologous). This set make a homologous pair.
A homologous pair is a pair of chromosomes  (one chromatid from each parent) joined to together at the centromere.
They have the exact same gene - but may have different alleles of these genes.

6. Haploid and Diploid
Normal number of chromosome in a human body cell = 46
Diploid: having pairs of homologous chromosomes (2n)
These homologous chromosomes form 23 pairs
Haploid: having only 1 chromosome of each type/form (n)
All normal body cells are diploid

7. Diploid Parent Haploid Gamete Diploid Offspring
2n n
2n n n

8. If two separate gametes combine to make one cell, Why don’t we end up with a billions chromosomes? Reproductive cells have half the number of chromosomes as regular cells.
Each species has particular number of chromosomes in their cells.
When fertilization occurs, genetic material from the male and female gametes combine to form a single cell.
What does that tell you about the number of chromosomes in human gametes

9. Each parent contributes one chromosome of each pair to its gametes.
Because gametes will combine their chromosomes, each must contain only half the number of chromosomes.
This ensures the correct number of chromosomes in each offspring and from one generation to the next. ce

10. How do gametes end up haploid?

11. Meiosis
Type of cell division cells undergo to reduce the number of chromosomes from diploid to haploid, resulting in four gametes.
Consists of 2 parts: Meiosis I and Meiosis II
After Meiosis I, two new cells have been produced
After Meiosis II, a total of 4 cells have been produced.
Offspring are genetically different from parents and each other
Diploid Cell Divides twice to produce four haploid gametes

12. Video Amoeba Sisters Meiosis

13. Meiosis

14. Meiosis I: First Cell Division-Two diploid cells produced

15. Prophase I Nuclear membrane breaks down,
chromosomes condense and homologs pair up, forming a tetrad

16. Metaphase I spindle fibres guide chromosome movement.
Homologous pairs (tetrad) line up at equator of the cell (metaphase plate).
Prophase I- Nuc membrane breaks down, chromosomes condense and homologs pair up, (tetrad)
Metaphase I – spindle fibres guide chromosome movement. Homologous pairs (tetrad) line up at metaphase plate.
Anaphase I – homologous chrom pairs separate and move to each end of cell.
Telophase I - two nuclei form and each nucleus contains a complete copy of the cell’s DNA, cell divides.

17. Anaphase I
homologous chromosome pairs separate and move to each end of cell.
Prophase I- Nuc membrane breaks down, chromosomes condense and homologs pair up, (tetrad)
Metaphase I – spindle fibres guide chromosome movement. Homologous pairs (tetrad) line up at metaphase plate.
Anaphase I – homologous chrom pairs separate and move to each end of cell.
Telophase I - two nuclei form and each nucleus contains a complete copy of the cell’s DNA, cell divides.

18. Telophase I and Cytokinesis
Two nuclei form and each nucleus contains a complete copy of the cell’s DNA
Cell divides.
Prophase I- Nuc membrane breaks down, chromosomes condense and homologs pair up, (tetrad)
Metaphase I – spindle fibres guide chromosome movement. Homologous pairs (tetrad) line up at metaphase plate.
Anaphase I – homologous chrom pairs separate and move to each end of cell.
Telophase I - two nuclei form and each nucleus contains a complete copy of the cell’s DNA, cell divides.

19. Meiosis II: Second Cell Division
Prophase II – nuc membrane disappears, DNA still exists as chromosomes (does not need to condense), new spindle forms.
Metaphase II – sister chromatids line up along middle
Anaphase II – sister chromatids separate, and go to each end of the cell
Telophase II – four nuclei formed. Cytokinesis begins Cells divide, forming four new haploid cells.
After meiosis I, homologous chromosomes are no longer in the same cell so metaphase II is the single file arrangement of sister chromatids in the middle. In short, Metaphase I is the separation of homologous chromosomes. Metaphase II is the separation of sister chromatids.

20. Prophase II Nuclear membrane begins to disappear
DNA exists as chromosomes
A new spindle forms around the chromosomes
Prophase II – nuc membrane disappears, DNA still exists as chromosomes (does not need to condense), new spindle forms.
Metaphase II – sister chromatids line up along middle
Anaphase II – sister chromatids separate, and go to each end of the cell
Telophase II – four nuclei formed. Cytokinesis begins Cells divide, forming four new haploid cells.
After meiosis I, homologous chromosomes are no longer in the same cell so metaphase II is the single file arrangement of sister chromatids in the middle. In short, Metaphase I is the separation of homologous chromosomes. Metaphase II is the separation of sister chromatids.

21. Metaphase II
Chromosomes (sister chromatids) line up along the middle of the cell
Prophase II – nuc membrane disappears, DNA still exists as chromosomes (does not need to condense), new spindle forms.
Metaphase II – sister chromatids line up along middle
Anaphase II – sister chromatids separate, and go to each end of the cell
Telophase II – four nuclei formed. Cytokinesis begins Cells divide, forming four new haploid cells.
After meiosis I, homologous chromosomes are no longer in the same cell so metaphase II is the single file arrangement of sister chromatids in the middle. In short, Metaphase I is the separation of homologous chromosomes. Metaphase II is the separation of sister chromatids.

22. Anaphase II
Chromosomes (sister chromatids) separate and go to each end of the cell
Prophase II – nuc membrane disappears, DNA still exists as chromosomes (does not need to condense), new spindle forms.
Metaphase II – sister chromatids line up along middle
Anaphase II – sister chromatids separate, and go to each end of the cell
Telophase II – four nuclei formed. Cytokinesis begins Cells divide, forming four new haploid cells.
After meiosis I, homologous chromosomes are no longer in the same cell so metaphase II is the single file arrangement of sister chromatids in the middle. In short, Metaphase I is the separation of homologous chromosomes. Metaphase II is the separation of sister chromatids.

23. Telophase II and Cytokinesis
Four nuclei form.
Cytokinesis begins - Cells divide, forming four new haploid cells.
Prophase II – nuc membrane disappears, DNA still exists as chromosomes (does not need to condense), new spindle forms.
Metaphase II – sister chromatids line up along middle
Anaphase II – sister chromatids separate, and go to each end of the cell
Telophase II – four nuclei formed. Cytokinesis begins Cells divide, forming four new haploid cells.
After meiosis I, homologous chromosomes are no longer in the same cell so metaphase II is the single file arrangement of sister chromatids in the middle. In short, Metaphase I is the separation of homologous chromosomes. Metaphase II is the separation of sister chromatids.

24. Check your understanding
What role does meiosis play in sexual reproduction?
What are the main differences between mitosis and meiosis?
What are the similarities between mitosis and meiosis II?
What’s the difference?
What’s the difference between meiosis I and meiosis II?
Mitosis: daughter cells are diploid and identical to the parent cell,
Meiosis: two cell divisions, produces gamets, four daughter cells, haploid and genetically distinct, homologous pairs (tetrad) crossing over
in both cases chromosomes line up and sister chromatids are separated by the action of the spindle fibers. The daughter cells are genetically identical to one another.
meiosis II there is a single member from each chromosome pair present, whereas in mitosis both members of each chromosome pair are present.
Meiosis I includes crossing over or recombination of genetic material between chromosome pairs, while meiosis II does not.
Meiosis II starts with two haploid parent cells and ends with four haploid daughter cells, maintaining the number of chromosomes in each cell. Homologous pairs of cells are present in meiosis I and separate into chromosomes before meiosis II
the only significant difference is that in meiosis II there is a single member from each chromosome pair present, whereas in mitosis both members of each chromosome pair are present.
Metaphase : mitosis - individual chromosomes align there Meiosis: meta I -  tetrads align on the metaphase plate.

25. Five Key Differences between Mitosis and Meiosis
# division 1 2
Daughter cells
2 identical diploid, daughter cells to parent
4 haploid, genetically different, gametes
Metaphase
Individual chromosomes align
Meta I tetrads align
Anaphase
centromeres divide
Ana I centromeres don’t divide, sister chromatids don’t separate
Five Key Differences
In meiosis, homologous chromosomes pair with each other (i.e., they form tetrads) and crossing-over occurs. In mitosis, neither of these things occur.
In metaphase I of meiosis, tetrads align on the metaphase plate. In metaphase of mitosis, individual chromosomes align there.
In anaphase I of meiosis, centromeres don't divide, and sister chromatids don't separate. In mitotic anaphase, they do.
In meiosis there are two successive divisions, ultimately producing four daughter cells. In mitosis, there is only one division and it produces two daughter cells.
Another important difference in comparing mitosis versus meiosis is that meiotic prophase I lasts far longer than does mitotic prophase. In fact, it is broken into several named substages, which is not the case for mitotic prophase.
Note, however, that meiosis II is very similar to mitosis (in that sister chromatids separate from each other in both) — the only significant difference is that in meiosis II there is a single member from each chromosome pair present, whereas in mitosis both members of each chromosome pair are present.

26. HOMEWORK
HW: Read p74-77, CYU p78 #1-3, 6-8, 11-13, 16, 17