BIOSC 0815 1st EditionLecture 9Outline of Last Lecture I. The Cell CycleII. Surface AreaIII. Phaseso G1o So G2o MIV. New CellsV. CheckpointsOutline of Current Lecture I. GametesII. MeiosisIII. Two partso Meiosis Io Meiosis IIo DifferencesCurrent Lecture- Correction from last week: There is no 4N in human cells!!! N: number of different typesor kinds of chromosomesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Ploidy: number of chromosomes in each typeo Haploid: gamete cells.o Diploid: 2N- Human cells have two copies of nearly every gene.- Gametes:o Egg and Sperm Cells are called gametes. They are special because when they arefully created, they contain half the amount of DNA of haploid cells. They have 23chromosomes. This is a haploid cell: 1N. o During fertilization we unite the egg and the sperm to make a zygote. This now has 46 chromosomes and is a diploid cell. o Egg (1N) + sperm (1N)  Zygote (2N)o Child gets half of the chromosomes from mother and half from father.o Homologue (chromosomes that will go together)o How do we get this number?- Meiosis:o Division by gamete stem cells to result in ½ DNA. It is similar to mitosis but the result is different.o Gametic stem cells (germ cells) these are cells that can divide by mitosis to replace themselves and also give rise to future egg or sperm.o Stem cells (able to become any kind of cell)o Process: Germ cell divides by mitosis will recreate itself and a new one. The new one will become and egg or sperm. Parent cell stays in location to continue to divide. o Special features: Total chromosome number reduced by half. Exchanges genes to produce new combinations which results in an increased diversity. This causes the variability of traits within species. (this doesn’t happen in mitosis, there you wouldn’t want to have variation).- Two major parts:o Gametes are produced in reproductive organs. Testes produce sperm in males, ovaries produce eggs in women. Sperm can be produced throughout the lifetimeof the male. The germ cells lining the walls undergo mitosis. The new cell produced undergoes meiosis to become sperm cells. Sperm cells are packed with mitochondria to produce ATP so the sperm can swim. Sperm cell formation results in four sperm cells in the process.o Eggs: the ovaries produce a fixed number of eggs in the embryo. There is a fixed number of eggs until at puberty ovulation cycle begins. The egg cell formation results in one ovum (only one egg cell survives) and three polar bodies. This onehas the largest amount of cytoplasm. Sperm doesn’t pass on a lot of stuff besides DNA. Egg has mitochondria and other organelles. o Meiosis 1: this is where the unusual events occur. Exchange genetic material between homologous chromosomes. Separate homologous chromosomes (but not the chromatids.) Line up in homologous pairs during metaphase I, not chromatids.  After cytokinesis is when you get 1N.o Meiosis 2: separate the chromatidso Meiosis consists of phases in which chromosomes are duplicated, moved, divided, and o Names are the same as for those in mitosis. But with I and II after them for meiosis I and meiosis II. Phases: Prophase I: spindles form, chromosomes are in pairs. Late prophase in meiosis is different because the homologous chromosomes are composed of paired sister chromatids. These homologous chromosomes come very close together and exchange information. They form a tetrad. Where information is exchanged are called sites of crossing over. After crossing over occurs, the chromosomes are called recombinant chromatids. - Because of this you now have some information from the father on the mother’s chromosome. And the same for the mother information being exchanged onto the father’s chromosome. - The advantage of doing this is that when you mix the genetic information, you have a better prepared organism.  Metaphase I: exchanged pieces of genetic material. The homologous chromosomes line up. They line up differently from mitosis. They do NOTline up single file in the middle of the cell. In meiosis I, homologous chromosomes line up across from one another in the middle of the cell.  Anaphase I: sister chromatids are still together. Homologous chromosomes are separated.  Telophase I: separate the cell. The new cells are both 1N, or haploid.  Then there is a brief interphase onto meiosis II. During this brief interphase no DNA replication occurs, and no nuclear envelope forms. Meiosis II is pretty much mitosis all over again. Meiosis II- Goal is to separate sister chromatids and end up with four cells. - Protophase II- Metaphase II: line up along middle of the cell.- Anaphase II: successfully separate the sister chromatids- Telophase II: packaging everything up into new cells. Wind up with four cells. o Differences between meiosis I and II Phrophase I vs II: Anaphase I vs II. In I we are separating homologous chromosomes, inn II we are separating sister chromatids Telophase I vs