MEIOSIS Reproduction Asexual relies on mitosis exact copies

MEIOSIS

Reproduction • Asexual (relies on mitosis): exact copies, DNA from one parent • Sexual (relies on meiosis): unique individuals, DNA from both parents

2 TYPES OF CELLS 1) BODY CELLS 2) SEX CELLS

Types of Cells: Body Cells All cells other than sex cells -Also called somatic cells -Made by mitosis This scanning electron micrograph (courtesy of Dr. Marion J. Barnhart) shows the characteristic biconcave shape of red blood cells.

Types of Cells: Body Cells -Contain 2 copies of each chromosome -called homologous chromosomes -have diploid #, 2 n EX. Humans =46

Types of Cells: Sex Cells *Also called gametes *Eggs and sperm *Made by meiosis *Have haploid #, n *EX. Humans =23

Sex Cells (sea urchin egg being fertilized)

Chromosome # Egg (haploid #) Ex. Humans 23 + 23 =46 Sperm (haploid #) ZYGOTE (diploid #)-fertilized egg

Meiosis: produces sex cells Reduction division -starts with 1 diploid cell and ends up with 4 haploid cells

Meiosis occurs in 2 steps MEIOSIS I AND MEIOSIS II

MEIOSIS I Meiosis I (P 1, M 1, A 1, T 1) - Chromosomes are copied. -Two new daughter cells are produced

MEIOSIS II Meiosis II (P 2, M 2, A 2, T 2) - Two sister chromatids are split into two daughter cells. - A total of 4 cells are created, they are not identical. - They have half the chromosomes of a body cell (non-sex cell).

Meiosis Diagram

Sperm Formation

Egg Formation (unequal cytokinesis)

Comparing Mitosis and Meiosis HOW MANY CELLS ARE MADE? Mitosis 2 Meiosis 4

Comparing Mitosis and Meiosis ARE RESULTING CELLS GENETICALLY THE SAME OR DIFFERENT? Mitosis Genetically the same Meiosis Genetically different

Comparing Mitosis and Meiosis WHAT TYPES OF CELLS RESULT IN THE PROCESS? (BODY CELLS OR GAMETES) Mitosis Body cells Meiosis Gametes

Comparing Mitosis and Meiosis WHAT IS EACH PROCESS USED FOR? Mitosis Growth and repair Meiosis Formation of sex cells and genetic variation