wk10, looking ahead to wk11

The Cell Cycle

In week 10 we discussed the phases of the Cell Cycle, and spent extra time on cell division, including mitosis.

First in the Cell Cycle our cells grow (G1 phase).  Then they replicate their DNA (S phase).  Then they grow some more, do checks for accuracy, and get ready for mitosis (G2 phase). These three phases together are known as interphase.

Once the cells are done with interphase they enter M phase, also known as cell division.

Ok, so we aren't really doing mathematical division.  It is actually more like multiplication, since we start with one and end up with two.  

Cell division is comprised of two parts - mitosis and cytokinesis. Mitosis is itself comprised of four phases - remember PMAT? Prophase, Metaphase, Anaphase, and Telophase.  Each step is important for orderly production of two identical daughter cells.

Looking Ahead to wk11

Cell division using mitosis is important to create additional somatic (body) cells for growth, or for replacement if the cell is damaged or destroyed. All of this happens within the same organisms.  Some organisms use very similar processes to create duplicate organisms. Examples of this are budding and binary fission. Binary fission is the common mode of reproduction in bacteria - each bacteria (made up of a single cell, but still a distinct organisms) makes a duplicate of itself to create additional bacterial organisms. These types of reproduction, where the new organism is an exact genetic copy of the parent organism, are called asexual reproduction.

Humans and a great many other complex organisms, use a different method of reproduction known as sexual reproduction, where two incomplete sets of DNA from two parent organisms combine to make a genetically unique offspring. In order to produce the needed special cells (called sex cells or gametes), which have only half of the genetic information (haploid), there is a similar but different process to mitosis and it's called meiosis.

So why go through this extra effort of creating cells that have half the genetic information (haploid) just to combine them with another haploid cell from a new organism with complete genetic information (diploid)? Why not just use asexual reproduction like starfish and bacteria and make little clones of ourselves instead? There are several reasons, but the big one is this: genetic variation.    We will take more about genetic variation in wk12 and when we discuss evolution, but for now know that genetic variation is what gives individual organisms of the same species variety - say in birds different feather coloring, different beak shape, different body size, different songs, etc.  It is this variety that allows the species as a whole to adapt to the environment.

Here are the readings and videos/resources for this week.  Don't forget to keep working on your vocabulary.

11 Sexual vs Asexual reproduction, ploidy, meiosis

RSO Ch. 9 Meiosis Divides by Two and Makes You

LOE Ch 12 Intro-Review

CK12 BC 2.36-2.40

CK12 LSC 2.20-2.22

Chromosome Numbers in Mitosis - transition, Amoeba sisters cover the number of chromosomes at different stages in mitosis and meiosis Meiosis The Great Divide - transition, Amoeba sisters do an overview of meiosis and gamete formation Meisosis Square Dance - both, Ok, this is funny! But it can also be a good way to remember the phases of meiosis, and what happens at each.  You can use this worksheet that has the lyrics and  questions to clarify the steps Sexual vs Asexual Reproduction - both, this is an interactive to quiz your understanding of what organisms use sexual reproduction, asexual reproduction, or both. Meiosis - scholar, Crash Course covering meiosis and the production of gamete cells