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.

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.

Chromosome Conundrum How many chromosomes do you have? Where did they come from? How is this possible?

Sexual Reproduction Organisms that use Sexual Reproduction must half the number of chromosomes in special process called meiosis to produce special cells called gametes. We have two types of cells...

Somatic Cells: Body Cells Somatic Cells are 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)

Gametes: Sex Cells Sperm (male gametes) Ova or egg (female gametes) Created by process called meiosis Contain only a single set of chromosomes, (haploid number, n)

Haploid and Diploid Diploid number, 2n, means a cell contains two complete sets of chromosomes, one from each parent. (pairs of homologous chromosomes Somatic cells are diploid, 2n. Humans have 23 pairs of chromosomes, 2n =46. Haploid number means having only 1 chromosome of each type/form (n) Only gametes are haploid.

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). They have the exact same gene - but may have different alleles of these genes.

Diploid Parent Haploid Diploid Gamete Offspring 2n n 2n n 2n

If two separate gametes combine to make one cell, Why don’t we end up with a billions chromosomes? Reproductive cells (gametes) must 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

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

How do gametes end up haploid?

Meiosis Type of cell division where cells 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

Video Amoeba Sisters Meiosis https://www.youtube.com/watch?v=fcGDUcGjcyk

Meiosis

Meiosis I: First Cell Division-Two diploid cells produced

Interphase

Prophase I Nuclear membrane breaks down, chromosomes condense and homologs pair up, forming a tetrad Crossing over may occur.

Tetrad A tetrad is two homologous chromosomes, each composed of two sister chromatids. The two homologous chromosomes will align next to each other. But, since each is made up of two sister chromatids it will look like a group of four.

Crossing Over Crossing over is when a piece of chromosome breaks off and joins onto its homologous partner. Crossing over only occurs during Prophase I Adds to genetic diversity

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

HOMEWORK HW: Read p74-77, Answer CYU p78 #1-3, 6-8, 11, 13, 16 Complete guide notes

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.