Mitotic Cell Division
• Consider that the average person is made of ~10 to 100 trillion cells. • How many of you took a shower today? • We appreciate it! • But you washed many cells down the drain, as you lose an average of 1% of your cells each day. • If there was no replacement of cells, you would be gone in 100 days! Fuzzy math. • But cell division is important.
Cell Division in Eukaryotes Defined: the process by which cells reproduce. Two types of cell division in eukaryotes: 1. Mitotic cell division. Produces the body (soma). It is used for growth, replacement of old or dead cells, or for repair of damaged tissues. 2. Meiotic cell division. Produces eggs and sperm (gametes) in animals. Today we will address mitotic cell division. 3. Binary fission is a 3 rd process by which prokaryotic cells reproduce (we will not study this process).
Eukaryotic DNA • DNA is complexed with proteins and is present as multiple, linear chromosomes in eukaryotes. • Chromosomes first discovered by Walther Flemming in 1882 (German embryologist). -He coined the term mitosis which means “thread” in Greek. Drawing from Flemming’s book, 1882
Chromosome Basics Before we address mitotic cell division, we must address all the following topics. They seem numerous, but this is a complex idea that requires a strong foundation. Well worth our time. • Chromosome Number • Ploidy • Chromosome Structure • Homologous Chromosomes • Unreplicated and Replicated Chromosomes • Karyotypes • DNA Packaging/Chromatin Scanning electron micrograph of chromosomes.
Haploid, Diplod, Homologous, Replicated, Duplicated, Chromatids, Chromosomes… AAArrrrggg ghh! Don’t let this happen to you — Learn Learn chromosome basics!
Chromosome Number • Number of chromosomes is a species specific attribute, but is not directly related to complexity (more chromosomes does not equate to having more genes or being more advanced). • Ant*, penicillin fungus: 2 chromosomes • Fruit fly: 8, nematode worm: 4 chromosomes • Human: 46 chromosomes (know this one) • Dog: 78 chromosomes, Cat: 38 chromosomes • Fern: 1,262 chromosomes • *Jack Jumper Ant
Your picture here 2 2 8 4 46 78 38 1,262 Chromosome numbers of some species. I bit Mr. Charters’ High School algebra teacher!
Ploidy Defined: number of complete sets of chromosomes in the cells of an organism. Used to describe a cell or an organism. Two main categories of ploidy to know: 1. Haploid: having one set of chromosomes per cell (n). 2. Diploid: having two sets of chromosomes per cell (2n). In sexually reproducing organisms you get one set from mom and one set from dad. And a third category, polyploid: having multiple sets. Every diploid cell contains all the genes and chromosomes of an organism. Cells are differentiated by which genes are “turned on.”
Ploidy of Human Cells • Virtually all cells in humans , except gametes (eggs, sperm), are diploid (2n); that is they have two complete sets of chromosomes.
- Spring '12
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