Chapter 1

Who am I?

Billions of years ago, living organisms came into existence and so did I.  No organism could exist without me.  I live in every organism, from the complex, multi-celled humans, all the way to a virus. (By the way, all words written in italic are explained in the Glossary section at the end of this book.)

I am the source of information that is passed from one generation to the next.  Thus, I ensure diversity and survival of the species. Changes in the structure and organization of my entity provide the basic of random variations that support evolutionary changes.

Can you guess who I am?

      The DNA

Did you ever squirm in delight, or horror, when your parents’ relatives or friends came up to you and said, "Oh, goodness gracious! You look just like your mom!" Well, there is a lot of truth to that. Half of you comes from your mother and the other half comes from your father. And, you have a blending! This phenomenon is called heredity.

My name is Gene and I am the unit of heredity, which carries information from one generation to the next.

Chapter 3

Heredity

Gregor Mendel walks into his private garden wondering about the result of his latest experiment.  He knows that pollinating identical pea plants will produce offspring identical to the parents. But this experiment is different; he has pollinated garden peas that are not identical.  In fact, one parent is tall, and the other is short.

What do you think Gregor finds? Are all the offsprings tall? Short? A mix?

Gregor stares at the newly sprouted garden peas.  They are all tall.  Gregor looks at his notebook and records, “First generation (F1): all tall.”  (See F1 generation in Figure 15: The Pea Plant 1.)  From his experiment, the monk concludes that the trait tall is dominant, because all the offsprings are tall; while the trait short is recessive, because it doesn’t appear in any of the F1 generation.

                                                                         
                                                                      Gregor Mendel

Mendel's First Hypothesis

From his initial observation, Gregor forms a hypothesis, which he hopes will eventually prove correct. “Soon, dear peas, you will self-pollinate.  Don’t disappoint me!” he says to the plants, after pollinating the F1 generation with each other.

During the next several weeks in the year 1865, new garden peas emerge.  Gregor enters his favorite retreat and, with eager steps, walks to his sprouting babies.

He bends down to look at his experiment in progress.  A wide smile crosses his face.  “Aha! As I expected!”

What did he expect?  What would you expect the new pea plants to look like?  

  A Clue: According to Gregor, each plant carries two copies of a hereditary component.  These two copies are referred to as alleles. One allele comes from one parent, the other from the other parent. 

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