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3.1: Cells and Chromosomes

Difficulty Level: At Grade Created by: CK-12
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How does the individual develop certain characteristics?

We can identify a species by a list of unique traits that are shared by all members of that species but not shared by members of other species. Variations of those same traits also can help us distinguish individuals within the species from one another. Anyone who studies genetics is interested in the biological causes of traits and variations. Geneticists ask questions such as, “Why does Paul have blue eyes when his mother and father both have brown eyes? What color might the kittens be if a black cat and a gray cat reproduced?” Notice that the first question requires an explanation. It is a question about something that has happened. The second question requires a prediction. It asks about something that may happen or is going to happen. Geneticists solve problems that help them explain and predict the inheritance of traits and variations. (Notice the last sentence had six words that were italicized. Those six, italicized words have special meaning to scientists. Make sure you know the meanings of all these words!)

“Most of modern genetics is nothing more than a search for variation. Some of the differences can be seen with the naked eye. Others need more sophisticated methods of molecular biology.”

-The Language of Genes,

Steve Jones

To solve problems that explain and predict traits and variations, you have to know some things about cells. All living organisms are composed of cells. Cells work like little factories doing all the jobs inside your body that are needed to keep your body functioning. Your body is made up of many different kinds of cells such as skin cells, muscle cells, and nerve cells. Some cells look like squashed bricks, some look like doughnuts, and many have irregular shapes. However, every cell, no matter what its job, has the same basic parts.

All human cells have an outer border that is the boundary of the cell. This boundary is called the cell membrane. A liquid material called cytoplasm is inside the cell membrane. There is a large structure suspended in the cytoplasm called the nucleus. The nucleus is the part of a cell that contains the genetic information. The nucleus is surrounded by a nuclear membrane that, like the cell membrane, makes a boundary around the nucleus. With few exceptions, every cell in your body has a nucleus. Your mature red blood cells and the cells in the lenses of your eyes do not have nuclei. The cells that give rise to, or produce, your red blood cells and the cells in the lenses have nuclei. However, the mature cells do not.

Figure 2.1 Using a microscope, you can tell some cells apart by their appearance. How cells look often tells something about what they do.

Did You Know?
You have 60 trillion cells in your body. While some of your cells will be with you your entire life, other cells have a shorter life span and must make copies of themselves. Many of your body cells make copies of themselves every day, such as red blood cells.

Genetics in the News What is the news in genetics today? Which new discoveries are being made in the areas of genetics in human health? In agriculture, to develop new foods? In productivity of food, to increase quality, improve storage, or quantity? Find a news article related to genetics. Attach the article to a summary sheet on which you have included:

  • title;
  • source and date;
  • summary of contents;
  • your opinion of the article, supported by reasons;
  • explanation of how this relates to you; and
  • what more you would like to know.

Share your information with the class by creating a bulletin board or class resource file.

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Date Created:
Feb 23, 2012
Last Modified:
Jul 13, 2016
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