MAKING GAMETES THE SEXIEST OF THE CELLS Objective

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 Leopard Gecko n= 19 Dog n= 39; Daisy n= 9

Diploid Definition • A cell with a complete set of chromosomes is called a diploid cell. Represented by • 2 n 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 Nuclear Membrane Centrioles DNA • Same as mitosis • DNA in chromatin • Cells are growing and doing their normal cell jobs • DNA= 2 n

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