What do the terms “haploid” and “diploid” mean? Meiosis occurs in what type of cells? Reproductive cells (the ones that divide to form sperm and eggs) What is “reduction division?” Cell division that reduces the amount of DNA from parent cell to daughter cells In meiosis, the chromosome number is cut in half What do the terms “haploid” and “diploid” mean? Diploid refers to a cell that has two copies of every chromosome: 1 from mom and 1 from dad Haploid refers to a cell that has only 1 copy of every chromosome

Diploid (2N) cells = 46 chromosomes Haploid (N) cells = 23 chromosomes What are the diploid and haploid chromosome numbers in humans? Diploid (2N) cells = 46 chromosomes Haploid (N) cells = 23 chromosomes What are the only cells in a human that are haploid? Sex cells (gametes): sperm in males, eggs in females Why do gametes (sperm and eggs) need to be haploid? During sexual reproduction, a sperm cell fertilizes an egg cell and the two form a zygote. The zygote must be diploid. If the sperm and egg were diploid, they would create a polyploid zygote that could not survive.

Does interphase occur before meiosis? Yes, all cells go through G1, S, and G2 no matter what type of division they use What is the result of meiosis? 1 diploid (2N) parent cell produces 4 genetically different haploid (N) daughter cells What are the two major phases of meiosis called? Meiosis I and Meiosis II

tetrad Prophase I, Metaphase I, Anaphase I, and Telophase I What are the phases of meiosis I? Prophase I, Metaphase I, Anaphase I, and Telophase I What are homologous chromosomes? 2 chromosomes that contain the same genes for the same traits, but not necessarily the same alleles When homologous chromosomes pair up, they form a structure called a what? tetrad

Why do cells have homologous chromosomes? “Tetra” means 4. What does this have to do with a tetrad? A tetrad is made up of 4 sister chromatids (2 chromosomes each containing 2 chromatids) Why do cells have homologous chromosomes? Every cell gets 1 copy from mom and 1 copy from dad for every chromosome pair What happens during Prophase I? The nucleolus and nuclear membrane “break up” and temporarily disappear. Centrosomes and centrioles migrate to opposite sides of the cell Spindle fibers grow from the centrioles and radiate toward the center of the cell. Homologous chromosomes pair up to form tetrads and crossing-over can occur

It increases genetic diversity What is crossing-over? The process where homologous chromosomes exchange genetic information by crossing arms, breaking parts off of each chromosome, and switching the pieces Why doesn’t crossing-over occur in prophase of mitosis? Homologous chromosomes do not pair up to form tetrads in mitosis. Why is crossing-over beneficial? It increases genetic diversity

What happens during metaphase I? Spindle fibers attach to the tetrads and help line the tetrads up across the center of the cell on an imaginary line called the metaphase plate or cell equator What is the only difference between metaphase I of meiosis and metaphase of mitosis? In metaphase I of meiosis the tetrads line up, but in metaphase of mitosis, individual chromosomes line up What happens during anaphase I? Spindle fibers shorten, separating the homologous chromosomes. The chromosomes are pulled to opposite ends of the cell

What happens during telophase I? What is the only difference between anaphase I of meiosis and anaphase of mitosis? In anaphase I of meiosis, homologous chromosomes are separated, but the sister chromatids stay together. In anaphase of mitosis, sister chromatids are separated. What happens during telophase I? The nuclear envelopes reappear The spindle disappears Cytokinesis occurs What is the difference between the results of mitosis and the results of meiosis I? Mitosis produces 2 genetically identical, diploid daughter cells. Meiosis I produces 2 genetically different, haploid daughter cells.

Prophase II, Metaphase II, Anaphase II, and Telophase II What are the phases of Meiosis II? Prophase II, Metaphase II, Anaphase II, and Telophase II Does interphase occur before meiosis II? No, interphase only occurs before meiosis I. The two cells made from meiosis I go directly into meiosis II What happens during Prophase II? The nucleolus and nuclear membrane “break up” and temporarily disappear. Centrosomes and Centrioles migrate to opposite sides of the cell Spindle fibers grow from the centrioles and radiate toward the center of the cell.

What happens during Metaphase II? Spindle fibers attach to the chromosomes and help line the chromosomes up across the center of the cell on an imaginary line called the metaphase plate or cell equator What happens during Anaphase II? Spindle fibers shorten, breaking sister chromatids apart to form separate chromosomes. The chromosomes are pulled to opposite ends of the cell What happens during Telophase II? Chromosomes begin to unwind back to chromatin. The nuclear envelope and nucleolus reappear in each daughter cell The spindle disappears Cytokinesis occurs

How does meiosis II compare to mitosis? They are the same except the final result: mitosis produces 2 genetically identical, diploid daughter cells, but meiosis II produces 4 genetically different, haploid daughter cells. What is spermatogenesis? Meiosis that occurs in male reproductive cells to form sperm. What is oogenesis? Meiosis that occurs in female reproductive cells to form eggs (ova)

Why is only 1 egg produced in oogenesis? When cytokinesis occurs, the cytoplasm is divided unevenly. Only the cell that gets the most cytoplasm forms an egg. The other 3 cells are called polar bodies and they do not participate in reproduction. What is this phase? Prophase I Metaphase I

Anaphase I Telophase I Prophase II What is this phase?

What is this phase? Metaphase II Anaphase II Telophase II