Meiosis From one, arise four. Each unique. Numbering half, no more. “…in me junk” From one, arise four. Each unique. Numbering half, no more.

Meiosis: How to make sex cells. Living things inherit a single copy of each gene from each parent. This means that you are half your maternal parent and half your paternal parent.

Gametes Sex cells aka Reproductive cells Sperm in male organisms Egg in female organisms A gamete is defined as a cell that fuses with another cell during fertilization in organisms that reproduce sexually.

Diploid Haploid Di = two Ploid = number of chromosomes All body cells Ha = half Ploid = number of chromosomes Only gametes

Homologous Chromosomes Each cell in your body has two sets of each chromosome. One from mother and one from father. The chromosomes from mom and dad have the same genes in the same places, but possibly different versions.

Paired up Chromosomes chromatids After Interphase Chromosome One DAD MOM

Meiosis is the creation of gametes Meiosis is also known as gametogenesis Gameto: Sex cell Genesis: creation THE TEXT BOOK SAYS: Meiosis is a process in which the number of chromosomes per cell is divided in half (creating haploid cells through the separation of homologous chromosomes that have crossed over in a diploid cell.

The Cell Cycle? Interphase

Meiosis Meiosis starts with a germ cell. Germ cells (PGCs) are cells that will become gametes after meiosis.

Germ Cells A germ cell starts out as a cell that has both sets of homologous chromosomes and is said to be diploid. Remember: Diploid means two sets of chromosomes. INTERPHASE Germ Cells must replicate their DNA during the “S-Portion” of Interphase

REVIEW: DNA Replication

Meiosis One At the end of this step: Two cells form. Each cell has sets of chromosomes and alleles that are different from each other and from the original cell.

Meiosis One – Prophase One At the start of prophase I, the chromosomes have already duplicated. During prophase I, they coil and become shorter and thicker and visible under the light microscope. Prophase I is the longest phase of meiosis, typically consuming 90% of the time for the two divisions.

PROPHASE ONE IS THE MOST IMPORTANT PART OF MEIOSIS!!!!

Prophase One - Crossing Over Genetically Recombined Chromosomes TETRAD: Tetra = four “Four-Chromatids”

Prophase One = GENETIC VARIATION As a result of Prophase One: the maternal and paternal chromosomes got all mixed up so that each is now a little MOM and a little DAD. WHY?

Meiosis One – Metaphase One The sets of tetrads line up in the middle of the cell. Spindle fibers push and pull the tetrads.

Meiosis One – Anaphase One The tetrads separate. The newly separated chromosomes are pushed and pulled to the opposites sides of the cell.

Meiosis One – Telophase One & Cytokinesis

Move directly into Meiosis Two NO INTERPHASE !! Move directly into Meiosis Two

Meiosis Two – Prophase Two The chromosomes condense, nucleus breaks down and the spindle fibers begins pushing and pulling the chromosomes.

Meiosis Two – Metaphase Two The chromosomes line- up in the middle of the cell having been pushed and pulled by spindle fibers.

Meiosis Two – Anaphase Two The chromosomes separate and are pulled/pushed to the opposite sides of the cell.

Meiosis Two – Telophase Two & Cytokinesis

Once Meiosis is finished… When complete the results will be either: Four sperm cells each different from the other OR One egg cell and three small polar bodies. Cells that are destroyed to make sure that only one egg is made.

Meiosis in Males Spermatogenesis The process by which sperm is produced in male animals. Spermatogenesis occurs in testes. 1.During Meiosis I the diploid cell increases in size becoming a germ cell to undergo Meiosis. 2.The larger germ cell undergoes Meiosis II to form 4 haploid cells, which develop tails and become sperm.

Meiosis in Females Oogenesis The process by which an ovum is produced in female animals. Oogenesis occurs in ovaries. 1. During Meiosis I & II the cytoplasm divides unequally. 2. The larger germ cell undergoes Meiosis to an egg cell the other cell called a polar body eventually dies.

Males vs. Females