Making gametes; the sexiest of the cells Objective: describe the process of meiosis and compare the processes of meiosis and mitosis

Different organisms have different numbers of chromosomes Scientists use the letter n to represent the number of chromosomes each organism has Human n= 23 Dog n= 39; Daisy n= 9 Leopard Gecko n= 19

Diploid Definition A cell with a complete set of chromosomes is called a diploid cell. Represented by 2n to show a complete set of chromosomes

Haploid Definition Cells that carry only half the genetic material of the parent are referred to as haploid cells. Represented By n to show half the diploid number

Sexual Reproduction

Sexual Reproduction Requires 2 sex cells (sperm and egg) Also called gametes Unite to form diploid cells

Meiosis Sex cells are produced by a process called meiosis 2 Stages: Meiosis I and Meiosis II Makes 4 new cells, each with half the DNA of the parent cells

Stages of Meiosis Meiosis I

Interphase Same as mitosis DNA in chromatin Centrioles DNA Nuclear Membrane Same as mitosis DNA in chromatin Cells are growing and doing their normal cell jobs DNA= 2n

Prophase I DNA condenses into chromosomes and homologous chromosomes pair (homologous= carry same genes) These chromosome pairs are called tetrads Crossing over occurs in this step

Crossing Over Parts of homologous chromosomes are exchanged

Metaphase I Like metaphase in mitosis Chromosomes like up in the center of the cell Nuclear membrane now gone

Anaphase I Homologous chromosomes are pulled to the opposite ends of the cell Reduction step- each side only getting half of DNA

Telophase I and Cytokinesis Nuclear membrane reforms Cytoplasm is divided between the two cells DNA= n