Download Getting to Know: Genes

Getting to Know: Genes
You have probably noticed that many people
resemble their biological parents. They may
share traits such as body type, hair texture,
skin tone, and shapes of facial features. Traits
are passed from parents to offspring by
the inheritance of genes. Genes are units of
genetic information. All organisms contain
genetic information in their cells. The genetic
information is encoded in DNA. Molecules of
DNA are extraordinarily long. They condense, or
wind up, forming structures called chromosomes.
A gene is a segment of a chromosome that
codes for a single protein or part of a protein.
Proteins are responsible for all of an organism’s
inherited traits.
Mothers and daughters share many
traits because they share many of the
same genes. Each child inherits half of
her genes from her mother and half of
her genes from her father.
How did I inherit genes from my parents?
Human DNA is organized into 23 chromosomes. Each of our body cells contains two copies
of each chromosome for a total of 46 chromosomes. You received one complete set of
23 chromosomes from your mother and another set of 23 chromosomes from your father.
This works because human sex cells have 23 chromosomes, and two sex cells join to form
a zygote with 46 chromosomes. When the body produces sex cells, chromosome pairs
separate and sort randomly into each sex cell. That means sex cells produced by the same
person have different combinations of chromosomes. Siblings (other than identical twins)
have different traits because they inherit different combinations of chromosomes from
each parent.
Misconception 1: Is each of my genes a blend of my parents’ genes?
That’s not exactly correct. Actually, genes come in pairs. Because each of your cells has
two full sets of chromosomes, you have two distinct genes for every trait—one from
each parent. Which genes get expressed as traits depends on factors you will learn more
about in the lesson.
Concept: Genes
Getting to Know
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Can you explain more about the link
among proteins, genes, and traits?
Proteins form the building blocks for all the structures
in your body. Hair, skin, organs, blood, teeth, bones,
and all the other parts of your body you can think of
are made of proteins. Proteins also control many of
your body’s functions. Special proteins called enzymes
help your cells perform chemical reactions that drive
life processes.
Your cells use the information in a gene to create a certain protein or part of a protein. That protein affects one or more traits. Most traits, like eye color and hair texture, are controlled by more than one gene. A few traits, like dimples, are controlled by a single gene. Although genes control inherited traits, they do not control everything about a person’s physical traits or behaviors. The environment plays a role, too. For example, a person may have the genetic ability to discern musical pitches. Whether or not the person becomes a musician depends on exposure to instruments and musical learning
experiences. A gene for dimples causes the body
to create a certain protein that forms
dimples in the skin.
Misconception 2: Our traits change as we grow older because we take in new
genes from the environment over time.
That’s not correct. People’s traits do change as they age, but this is not a result of genes
changing. In fact, we have the same genes for our entire lives. Changes that occur with
aging happen for other reasons.
In addition, genes are not found anywhere in the environment other than in the cells
of organisms. Although we do eat organisms, we cannot acquire new genes by eating
them. The only natural way to get genes is to inherit them from your biological parents.
However, gene therapy is a new and developing medical practice that aims to replace
broken genes with healthy ones.
In the lesson, you will learn much more about how cells use information in genes to create
proteins. You will also learn what determines which genes in a pair are expressed as traits.
In most cases, only one gene in a pair is expressed. In some cases, both genes are expressed.
There’s a lot of information to cover, so let’s get started!
Concept: Genes
Getting to Know
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© Discovery Education. All rights reserved.
Discovery Education is a subsidiary
of Discovery Communications, LLC.