Add to Notes Stem Cells and Differentiation

Cell Division Unit 6

Cell Division All living cells come from pre-existing cells. New cells are made by cell division. A typical cell goes through a repeating process of growth, development, and reproduction called the cell cycle.

The Cell Cycle 1.Interphase: cell growth and development, DNA copied 2.Mitosis: nucleus divides 3.Cytokinesis: cytoplasm divides

Cell Cycle Most cells spend over 90% of time in interphase. Interphase contains: -G1:normal routine, cell growth -S: DNA copied (synthesis) -G2: prepares to divide

Cell Cycle Checkpoints Points where cell cycle is paused Don’t want all cells dividing unless there is a need for growth and repair. Cancer: uncontrolled growth of cells – Occurs because of mutations in genes that cause cells to continually divide. – Something that causes mutations is a mutagen. Carcinogens cause mutations that lead to cancer (cigarette smoke, UV light…)

Genetic Material in Cells DNA: molecule that carries genetic information Gene: segment of DNA that codes for one trait (humans have about 25,000 genes) Chromosome: Genes are packaged in bundles called chromosomes. (humans have 46) For the amount of genetic material to stay the same, chromosomes must be copied before the cell divides. DNA Chromosome

Duplicating Cell Structures Centrioles Spindle fibers Sister Chromatids C B

Duplicating Cell Structures Sister chromatids: identical copies of chromosome held together at the centromere. Centrioles: anchor spindle fibers Spindle Fibers: pull chromosomes to ends of cell CHROMOSOME

Interphase Normal cell processes occur. When the cell is ready to divide, chromosomes are copied in S phase.

Stages of Mitosis #1 Prophase Chromosomes condense & become visible. Nuclear membrane breaks down Spindles attach to chromatids

Stages of Mitosis #2 Metaphase Chromsomes line up in the middle – at the metaphase plate.

Stages of Mitosis #3 Anaphase Identical chromatids pulled apart to opposite ends of the cell.

Stages of Mitosis #4 Telophase Two new nuclei re-form.

Cytokinesis Cytoplasm divides. In plants, cell plate forms. In animals, cleavage furrow forms. Cytokinesis Video

Results of Mitosis (Asexual Reproduction) 1.2 identical daughter cells are formed 2.Cells are diploid (46 chromosomes) 3.Makes somatic (body) cells 4.Purpose: growth and repair

So What's the Big Idea? Mitosis is the process of dividing to create two genetically identical daughter cells from the parent cell. Why? Growth/repair

QUIZ – What stage are they in? #1 #4 #2 #3 #5 #6 #7

Meiosis Unit 6

Meiosis GOAL #1: Make cells for sexual reproduction – Sex cells are called gametes Sperm, Eggs – Gametes come together in fertilization to make a zygote – a fertilized egg. GOAL #2: Create genetic variation – Mix up mom and dad’s genes to get new combinations

Homologous Chromosomes Body cells are diploid. – Diploid = 2 copies of each chromosome – We have 23 pairs of homologous chromosomes Each pair has one chromosome from mom and dad Same size and genes. Different information (Mom – blue color for eyes, Dad – brown color) Sex cells are haploid – Haploid = 1 copy of each chromosome – Sperm and eggs

Karyotype: shows pairs of chromosomes Chromosomes #1-22: autosomes Chromosomes #23: sex chromosomes XX = female, XY = male

Karyotype: used to detect genetic disorders Non-disjunction: chromosomes don’t separate correctly in meiosis Monosomy: only one copy of a chromosome Trisomy: three copies of a chromosome

Meiosis Animation

Meiosis Two cycles of PMAT (prophase, metaphase, anaphase, telophase + cytokinesis) Since the cell divides twice, the chromosome number is cut in half

Genetic Variation 2. Independent Assortment Chromosome can line up in various ways during metaphase - animationanimation 1. Crossing Over Homologous chromosomes switch genes during 1 st Prophase. This produces unique chromosomes.

Oogenesis and Spermatogenesis Oogenesis: production of eggs (aka. ova) – Creates 1 functional egg and 3 polar bodies (non- functional) Spermatogenesis: production of sperm – Creates 4 functional sperm

What’s the advantage of meiosis? Daphnia: What's the point?

What’s the advantage of meiosis? Meiosis and sexual reproduction make new gene combinations More genetic variation among individuals of a population means some members will be able to survive in changing or difficult conditions.

Asexual vs. Sexual Reproduction Asexual Reproduction – 1 parent – Offspring are identical (clones) – Little time and effort needed – Produces many offspring – Called binary fission in prokaryotes Sexual Reproduction – 2 parents – Offspring are unique (traits from both parents) – More time and effort needed – Produces fewer offspring – Creates more genetic diversity

Meiosis Review Video Click for video

Results of Meiosis 1.4 different daughter cells are created 2.Cells are haploid (23 chromosomes) 3.Makes gametes – sperm (4) and egg (1)