Mitosis and Meiosis Notes

Important info, before we begin… Chromosome: a rod-shaped structure, usually found in pairs in a cell nucleus that carries genes that determine the characteristics of an organism. Tons of DNA is all coiled up inside each of these chromosomes A human body cell usually contains 46 chromosomes (23 pairs)

Organisms can reproduce sexually or asexually Asexual Reproduction Single parent passes all genes to offspring Identical “clones” of parent Entire population of species is identical Common in unicellular organisms

PROKARYOTIC CELLS DIVIDE ASEXUALLY These are unicellular organisms (bacteria normally) Their cells possess a single chromosome, containing genes The chromosome is replicated The cell then divides into two cells, a process called binary fission Prokaryotic chromosomes Figure 8.3B

Division into two cells Binary fission of a prokaryotic cell Prokaryotic chromosome Duplication of chromosome and separation of copies Continued growth of the cell and movement of copies Division into two cells Figure 8.3A

Sexual Reproduction Unique combination of 2 parents genes; each contributing half the offspring’s DNA Combination of parental genes and traits Wide variation in physical and behavioral traits Common in multicellular organisms

A little bit of review… What is a prokaryotic cell?

A little bit more review… True or False: You are made up of Eukaryotic cells.

WORK IT… Sexual vs. Asexual Worksheet

THE EUKARYOTIC CELL CYCLE AND MITOSIS A eukaryotic cell has many more genes than a prokaryotic cell The genes are grouped into multiple chromosomes, found in the nucleus Chromosomes contain a very long DNA molecule with thousands of genes Individual chromosomes are only visible during cell division Before a cell starts dividing, the chromosomes are duplicated This process produces sister chromatids

Chromosome distribution to daughter cells Chromosome duplication Sister chromatids Chromosome distribution to daughter cells

Mitosis

Why do we need more cells? What IS Mitosis? A way for the cell to make an EXACT copy of itself. Each daughter cell has EXACTLY the same DNA as the original cell. Why do we need more cells? To REPLACE old, worn out cells To REPAIR injuries To REPRODUCE (for some unicellular organisms) Cell division serves an important role in an organism's HEALTH and GROWTH. In an adult human, millions of cells divide each second to maintain homeostasis. Homeostasis = the organism and all its parts are stable and working properly so that the organism is healthy

MITOSIS Mitosis consists of 5 major phases: Interphase Prophase Metaphase Anaphase Telophase/Cytokinesis Figure 8.5

INTERPHASE DNA exists as chromatin. Growth and DNA replication occur centrioles DNA exists as chromatin. Growth and DNA replication occur 90% of a cell’s life cycle is in this stage Chromatin Nuclear envelope

PROPHASE Chromatin condenses to chromosomes. Spindle fibers form. Centriole Chromosome Chromatin condenses to chromosomes. Spindle fibers form. Nuclear envelope breaks up and the centrioles align at the poles. Spindles Centriole

(in middle of chromosome) Centriole METAPHASE Spindles Metaphase plate Chromosomes line up single file in the middle of the cell, perpendicular to the centrioles. Spindle fibers are attached to the centromeres. Centriole Centromere (in middle of chromosome)

ANAPHASE Spindle fibers retract, ripping the chromosomes in half at the centromere. Identical (daughter) chromosomes are pulled to the poles of each side of the cell. Centromere Centrioles Daughter chromosomes Spindle Fibers

TELOPHASE AND CYTOKINESIS Centriole Chromatin Chromosomes become chromatin. Nuclear envelope reforms, cleavage furrow develops in animal cells and the cell eventually splits. Cleavage furrow Chromatin Centriole

CYTOKINESIS Cytokinesis….This process pinches the cell apart Cleavage furrow Cleavage furrow Contracting ring of microfilaments Daughter cells

WORK IT… Virtual Mitosis Lab (access on class website) http://www.biology.arizona.edu/cell_bio/activities/cell_cycle/cell_cycle.html Amoeba Sisters Video on the basics of Mitosis (access on class website) https://www.youtube.com/watch?v=gwcwSZIfKlM Mitosis Drawing Worksheet Mitosis Mini Review

Meiosis

A Review of Sexual Reproduction: Unique combination of 2 parents genes; each contributing half the offspring’s DNA Combination of parental genes and traits Wide variation in physical and behavioral traits Common in multicellular organisms

You are a combination of two gametes (or sex cells) Cells with two sets of chromosomes (like your body cells) are said to be diploid (46 chromosomes) Gametes are haploid, with only one set of chromosomes (human sperm or egg cells = 23 chromosomes) 23 23 46 At fertilization, a sperm fuses with an egg, forming a diploid zygote which will give the resulting baby 46 chromosomes…. 23 from each parent

So, what is MEIOSIS?...The creation of sperm and eggs

10 Stages…… (If you include Interphase) MEIOSIS 10 Stages…… (If you include Interphase)

MEIOSIS I: Homologous chromosomes separate Interphase MEIOSIS I: Homologous chromosomes separate METAPHASE I ANAPHASE I Interphase Centrioles) Growth and DNA replication occurs. DNA exists as chromatin. Most of a cell’s life cycle is in this stage. Nuclear envelope Chromatin

Prophase I Chromatin coils up into chromosomes. Chromosomes, composed of sister chromatids, come together as pairs. The nuclear envelope breaks up. Spindle fibers form. “Crossing over” may occur between the chromosomes (see circles on diagram) Crossing over is when chromosomes come together and sections of the chromosomes are exchanged. This provides greater genetic variation. Spindle Fibers Centrioles Chromosomes

Metaphase I Centrioles The chromosome pairs line up in the middle between the poles. Spindle fibers are attached at the centromere. Spindle Fibers Chromosomes

Anaphase I Chromosome pairs are separated Spindle fibers grab chromosomes at the centromeres and pull them apart towards opposite poles and centrioles. Chromosomes Spindle Fibers Centromere Centrioles

Telophase I Cleavage furrow develops Nuclear envelope begins to reform. Double chromosomes start to uncoil. Eventually, the cell splits into two. Chromosomes Cleavage Centrioles

Now Meiosis II begins…. ***Make sure to draw arrows and label parts on each slide

Prophase II Spindle fibers form Nuclear envelope breaks up. Chromatin coils up into double chromosomes (composed of sister chromatids).

Metaphase II Double chromosomes line up single file in the middle of the cell. Spindle fibers are attached at the centromere.

Anaphase II Spindle fibers retract, ripping the double chromosomes in half at the centromere Single chromosomes are pulled apart towards the poles of each side of the cell

Telophase II Nuclear envelope reforms Chromosomes uncoil into chromatin Cleavage furrow develops in both cells and eventually splits into 4 sex cells (gametes), each with the haploid number of chromosomes.

MEIOSIS is different in BOYS and GIRLS OOGENESIS SPERMATOGENESIS *Made in the ovaries—Produces 4 cells but only 1 survives as an egg *Made in the testes—Produces 4 sperm

Work it… Haploid/Diploid Practice Meiosis Cartoon Project Meiosis Mini-Review

Let’s review some Similarities and Differences between Mitosis and Meiosis http://www.pbs.org/wgbh/nova/miracle/divide.html http://www.pbs.org/wgbh/nova/baby/divide.html