Monday, May 30, 2016

Meiosis Explained

Meiosis explained

by Christine M. Anderson

This article is a study guide for taking a test on the topic of meiosis. Important concepts are summarized and explained. By reading through this summary and studying what is written here, a student will be prepared to demonstrate an understanding of meiosis.
What is the most important general fact that should be understood about meiosis? It is a unique kind of cell division that takes place in the reproductive organs of organisms; organisms that rely on the survival strategy of sexual reproduction to produce offspring. In meiosis, cell division produces haploid gametes. Haploid gametes are sperm and eggs that have half the number of chromosomes as the somatic, or body cells.


Pay attention to the spelling of the word meiosis - M E I O S I S. It is pronounced MY OH SIS, with the emphasis on the first syllable. The name means: to diminish. This name makes sense because the number of chromosomes is being decreased by one half, when four gametes are formed from the original parent cell.
Know that the first phase of meiosis is prophase I. There is something that happens, during this phase, that is important to understand. During this prophase I, the chromatin condenses into chromosomes and the male and female pairs of chromosomes pair up to form tetrads. The root word tetra means four. A tetrad consists of two pairs of homologous chromosomes joined by a centromere. Homologous chromosomes are chromosomes that have the same genes, however the chromosomes may have different variations (alleles) of the genes. One important process that takes place during prophase I is "crossing over;" the exchanging of genetic material that occurs when two homologous chromosomes cross over each other and exchange genetic material. The word chromosome means "colored body," because the chromosomes take up the stain used to prepare cells for study under the microscope and are seen as distinct units, during prophase I.
The number of chromosomes found in the body cells of every member of a species is known as the diploid (2N) number of chromosomes. If the number of chromosomes in the parent cell is 12, the number of chromosomes in the sperm cell of the same organism will be 6. A zygote is formed when a haploid sperm fuses with a haploid egg to form a cell with the diploid, or same number of chromosomes as the parent cell.
It is also important to know that meiosis provides genetic variation in an organism's offspring. This is because each gamete has a different combination of chromosomes from independent assortment during meiosis. Also, the crossing over of chromosomes in prophase I shuffles the genes, so that the resulting germ cells are different and unique. The other phases of meiosis are metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II, and telophase II. Drawing the phases, describing what is happening during each phase, and labeling the cell structures and chromosomes helps one to study and become familiar with what is happening, step-by-step, during meiosis.

Tuesday, September 02, 2014

Video Clips that I show in Biology 1

Need a textbook to help you study?  A free online textbook can be found here:
CK-12 Biology is a high school FlexBook covering cell biology, genetics, evolution, ecology, microorganisms, fungi, plants, invertebrates, vertebrates, and physiology.
This book is available for download on your iPad with iBooks or on your computer with iTunes - FOR FREE!
You can follow my twitter account: @biology1teacher

If you would like to be a Citizen Scientist and participate in our bird watching project, you can register at http://ebird.org/content/ebird/ and submit your observations.  We have a birding hotspot here at Middletown High and you can watch birds at the pond and submit your observations to the Middletown High School Pond birding hotspot:  http://ebird.org/ebird/hotspot/L2346801   Check it out!

Click on the videos link to watch some of the videos that I show in class.
The Secret Lives of Scientists,
Mayim Bialik:
Globally Harmonized System of labeling chemicals in the workplace.  The video can be found here: 
Scientists in Action. We watched these two video clips:
The Tale of the Peacock
and Ancient Farmers of the Amazon
The Germ Theory.  The video clip starts at 11:49 minutes on this YouTube link:
Students wrote down the following questions in the Journal Section of their binders:
1.  How does the scientific meaning of a term like theory differ from the way it is used in everyday life?
2.  Can the "facts" of science change over time?
3.  Who was Charles Darwin?
4.  How did public opinion of his day affect Charles Darwin's willingness to publish the Origin of Species?
After watching the video, students answered the questions in their lab notebook.
Students may watch and review the video clips Isn't Evolution Just A Theory? and Who Was Charles Darwin? at this web site:
or on YouTube:

How Wolves Change Rivers as part of the Variation in Wolves activity.  The video can be found here:
Students wrote in their Journals the answer to the questions:  1.  What is Natural Selection?   2. Why is the relationship between the toxic newts and the garter snakes considered an evolutionary arms race?  3.  How does evolution really happen (work)? 

They watched a video called Toxic Newts that can be found at this link:


They also watched the video clip titled How Does Evolution Really Work? that can be found at this link:


As part of the Chicken Wings and Batter's Arms activity, students watched the video clip Common Past, Different Paths, which can be found at these links:
To understand the Whale's Tale project, students watched the video clip titled How Do We Know Evolution Happens? that can be found at this link:
and part of the video Part 1 of Walking with Prehistoric Beasts to see how the Ambulocetus lived.
To understand the characteristics of a modern whale, students watched 3 video clips: Alaskan Whales (which can be found as a file on bottom of this web page), Whale Song (which can be found at this web site
and Dolphins Blowing Bubble Rings (which can be found on my podcast link).
Students looked at the Evolution of Whales power point presentation, which can be viewed on this web site - scroll down to click on the file.
Students watched three videos about the Tiktaalik, a transitional fossil (see note 1 below for additional information):
Students watch a video about the evidence for evolution that summarized what we had learned.
Students looked at a variety of videos and web sites about human evolution:
Human Evolution Multimedia
Students watched a video clip: Did Humans Evolve? The video clip can be found at this web page:
However, the PBS video has become somewhat outdated.  So now, we watch this video about human evolution:
Great Transitions: The Origin of Humans — HHMI BioInteractive Video   https://www.youtube.com/watch?v=Yjr0R0jgct4
Students also watched this video clip: Becoming a Fossil. The video can be found at this web page:
Human evolution was demonstrated by observing this online activity:
This website ( http://www.becominghuman.org/ ) is used for an extra credit activity.  
This online National Geographic article contains a video clip that tells about Ida, the 47-million-year-old fossil
This web site has a video about the oldest fossil skeleton of a human ancestor:
and there is more information on my blog.
Students watched Debi's Story about antibiotic resistant tuberculosis, as part of a lesson about why understanding evolution is important now. They also watched a video about diseases.
Students watched a video titled: Why Is Evolution Important Now? This video is available to watch online at: http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html
Students learned about karyotypes:
Students watched two short video clips about Ryan White, after learning about hemophilia (a genetically inherited blood clotting disorder), which is a sex-linked genetic disease.  Ryan contracted AIDS after a transfusion of blood clotting protein that was a treatment for Ryan's hemophilia:
Students watched a video about Huntington's Disease as part of a lesson about pedigrees.  Here is the link:
Students watched a video clip about mitosis, cell division of somatic cells (asexual reproduction).  The video is copyrighted and cannot be posted.  However, the following link has videos that show real cells dividing:    
http://iknow.net/cell_div_education.html
Students participated in watching a Comparison of Mitosis and Meiosis annimation:
Comparison of Mitosis and Meiosis animation:
http://www.pbs.org/wgbh/nova/miracle/divi_flash.html
Students watched a video about the history of the discovery and the structure of DNA:

After studying protein synthesis, students watched video clips and animation:
https://www.youtube.com/watch?v=d1UPf7lXeO8  BioRap - DNA and Protein Synthesis

The Learn Genetics - University of Utah - Lick Your Rats Activity (epigenetics) can be found here:




From the Idea Bank, October 2015, Tips and Techniques for Creative Teaching by Ashley Campbell in the Science Teacher published by the National Science Teachers Association.
Science Videos on the Web:
Academy of Achievement:  www.achievement.org
Blick on Flicks:  www.nsta.org/publications/blickonflicks.aspx
Makers:  www.makers.com
"The Price of Progress":  http://cbsn.ws/1gd6RlM
The Secret Life of Scientists and Engineers:  http://to.pbs.org/laDSp2v

Note 1
For those who are interested in the Tiktaalik, there is an activity in this textbook:  SEPUP. (2011). Science and Global Issues: Biology. Lawrence Hall of Science, University of California at Berkeley.  Published by Lab-Aids, Inc., Ronkonkoma NY.  The activity is Evidence from the Fossil Record - Activity 6 pp. 446-453.  Students explore transitional fossils in an portion of the activity titled Studying Fossils to Determine the Origin of Tetrapods.  The Tiklaalik is one of the transitional fossils presented in the activity.  The videos listed above enhance interest in this activity.
There is also a 2011 episode of Mysteries at the Museum travel channel show where near the end of the episode, information is presented about the importance of the Tiktaalik fossil and it is explained that the fossil is housed at the Academy of Natural Sciences in Philadelphia, PA. http://www.travelchannel.com/shows/mysteries-at-the-museum/travel-guides/outlaw-shoes-and-astrochimp-travel-guide   It looks like the video would be on Disc 2 of Season 2 of the show that can be purchased from Amazon.com.  The episode is titled Outlaw Shoes, Astrochimp, and Message in a Bottle.  I have not purchased the video and am not 100% certain that it is on the CD.  If anyone reading this blog knows how to obtain the Mysteries at the Museum, Tiktaalik video or a video clip, please leave a comment.