Willis High School

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Mrs. Nickie Ehlert » Welcome!


 Hello everyone!
I am excited to begin a new year at Willis High School! This is my second year here and my first year teaching Biology.  I graduated from Anderson-Shiro Jr./Sr. High School and then went on to Sam Houston State University. I graduated with my Bachelor of Science degree in Biology with a minor in Wildlife Ecology. I'm very excited to meet everyone and cannot wait to get started!
Biology can be a rigorous course, but I am here to help facilitate learning and will answer as many questions as you have! The best way to reach me is by email, which you can find on the right side of the page. 
To keep up with what is going on in our class, please see the weekly agenda. 
 9:15-10:00 (3rd period)
7:20 - 8:13 - Biology
8:17 - 9:10 - Biology
9:14 - 10:07 - Conference
10:11 - 11:04 - Biology
11:08 - 12:42 - Biology
12:46 - 1:39 - Biology
1:43 - 2:35 - Biology
 Tuesday, Thursday, and Friday 2:35-3:15
Late Work Policies: 


Daily Assignments (40%)

Major Assignments (60%)

Late Penalty

25 points off grade

20 points off per day


Up to 2 days

Up to 2 days

  • Daily assignments (Example: Class work, homework, small labs, quizzes)
    • Late work will be accepted with a penalty of 25 points off per day. If the assignment is not turned in before day three, then the assignment will be graded as a zero.
  • Major Assignments (Example: Projects, major labs, tests)
    • Late work will be accepted with a penalty of 20 points off per day. The highest grade that will be given is a 60. If the assignment is not turned in before day three, then the assignment will be graded as a zero.
  • All assignments are due upon entering the classroom. If assignments are turned in after I have collected them, they are considered late.

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11.First filial generation

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Disruptions of the Cell Cycle Article

Introduction to Cell Cycle Control


Your body is constantly replacing old cells with new ones. In fact, your body makes millions of new cells every second! New cells are needed because at any given time some of your cells will reach the end of their life span and need to be replaced. You may also need new cells for growth or to repair damaged tissue. Cells go through a cell cycle to grow and divide in order to make new cells. 

The amount of time it takes to complete the cell cycle varies in different cells. Some cells divide quickly—even within a few hours. Other cells may take days to complete the cycle. No matter how long it takes, the entire cell cycle is regulated and predictable. For a long time, scientists didn't know how the cell "knew" when to move through the stages of the cell cycle. For example, how does a cell know when to start replicating chromosomes? Through experimentation, scientists have discovered that the cell cycle is regulated by certain proteins called cyclins.

Most cells move through the cell cycle with no problem. However, there are times when cells do not follow the rules of normal cell division. Cancer is a disease that can occur when control of the cell cycle is lost.

Regulation at Internal Checkpoints

It is essential that the daughter cells produced be exact duplicates of the parent cell. Mistakes in the duplication or distribution of the chromosomes lead to mutations that may be passed forward to every new cell produced from an abnormal cell. To prevent a compromised cell from continuing to divide, there are internal control mechanisms that operate at three main cell cycle checkpoints. A checkpoint is one of several points in the eukaryotic cell cycle at which the progression of a cell to the next stage in the cycle can be halted until conditions are favorable. 

The G1 Checkpoint

The G1 checkpoint determines whether all conditions are favorable for cell division to proceed. The G1 checkpoint, also called the restriction point, is a point at which the cell irreversibly commits to the cell division process. Nutrients, growth factors and DNA damage will be monitored at this checkpoint. A cell that does not meet all the requirements will not be allowed to progress into the S phase. The cell can halt the cycle and attempt to fix the problem, or the cell can enter into G0, the resting phase.

The G2 Checkpoint

The G2 checkpoint stops the cell from entering mitosis if conditions are not met. The most important role of the G2 checkpoint is to ensure that all of the chromosomes have been replicated and that the replicated DNA is not damaged. Cell size is also checked at this time. If the checkpoint mechanisms detect problems with the DNA, the cell cycle is halted, and the cell attempts to either complete DNA replication or repair the damaged DNA.

The M Checkpoint

The M checkpoint occurs near the end of metaphase. The M checkpoint is also known as the spindle checkpoint, because it determines whether all of the sister chromatids are correctly attached to the spindle microtubules.

Uncontrolled Cell Growth: Cancer

Cancer is a disease of the cell cycle. Cancer cells do not respond to the signals and safeguards that are in place. Because cancer cells don't respond appropriately, they grow uncontrollably and can eventually damage the tissues around them.  Cancer cells do not enter G0, so they repeat the cell cycle continuously.

If cancer cells continue to grow, they will eventually form a mass called a tumor.  Some tumors are benign and may be harmless. Malignant tumors are dangerous and can even cause death. Malignant tumors have the ability to leave their original growth site and move through the bloodstream to other areas of the body. This process is called metastasis. If this occurs, the tumor can invade new tissue and continue to grow uncontrollably in the surrounding tissue.