Below are some terms that are important in this unit. I have
explained each of these terms. However, I do not presuppose that my explanations are
definitions, and I don't want you to think of them that way.
You see, many students think it is possible to learn biology by
memorizing a list of important words and their definitions. However, I could define
any of the words below in many different ways. As an example, if I were going to
define myself, I could say any of the following:
If you were responsible for learning about me, and you only learned the definition of
"professor," you wouldn't really understand me at all. Does that make
Now imagine that I ask you about one of the terms below on a test.
Will you have learned enough about it that you can answer any question I throw out
on that term? Or will you only be prepared if I ask a particular question? The
difference here is also the difference between a passing grade and a less-than-passing
grade. So, on this first unit where you have a lot to study, start off on the right
foot and really learn about all this material, OK?
As you read Chapter 3, you may find that this list below helps you to understand the
terms that are given to you. But also, you might choose to use this list as a
review, to make sure that you understood everything you read. Either way, get
through the chapter and this list. OK?
| A characteristic that can be evaluated/understood
in some way. It can have more than one appearance, even many appearances. For
example, a trait could be something as like height; a person may be tall or short, but
those are both versions of their height trait. A trait can also be something that
isn't so obvious, like one's body's ability to regulate blood cholesterol levels; some
people's bodies can really regulate it, but other people cannot. With this type of
trait, it can be evaluated (with a blood test and study of one's personal habits), but it
isn't something that is apparent by looking at a person.
| This is one of those terms that we will be
learning about a lot during this semester. There are many ways of defining it, from
the very molecular level of biology to a more general definition. For now, you
should begin to understand that every trait is represented in a gene within an organism's
genetic code. So the genetic code is just the thousands of genes that define which
traits an organism should have (like we don't have any genes for producing that nasty odor
a skunk can produce) and which version of each trait we express (once we have the eye
color gene, does ours say that we will have blue, brown, hazel, green or some other
Mendel figured out that each gene actually
consists of two representations for the trait it defines. So, within our eye color
gene, we have two representations of eye color. (see "allele" below)
| Each version of a trait is represented within the
gene by an allele. You might have an allele for brown eyes and an allele for blue
eyes. Or you might have an allele for green eyes and an allele for hazel eyes.
Whatever the combination, you have two alleles for each trait within a gene.
And each allele just represents one possible version for that trait. Note
that there can be many, many alleles that exist within a population for one particular
trait (blue, green, hazel eyes, etc.), but each person only has two of these in their own
| The version of a trait that a person/organism
actually has. I have brown hair. So for the hair color trait, my phenotype is
brown. For the obvious traits, phenotypes are easy to describe because you can see
them. So-and-so is tall, or so-and-so has a deep voice, etc. Therefore, a
phenotype is the version of a trait that a person actually expresses.
| The allelic representation of a
gene. Meaning, which two alleles a person really has for any one
gene. The genotype is described using the words below (homozygous,
heterozygous, dominant, recessive). So, if your phenotype is blue
eyes, your genotype is homozygous recessive.
| The version of a trait that cannot
be hidden. A dominant allele is always expressed. That does
not mean that it is always the most common allele, just that if a person
has it, they will show it. For example, we tend to think of people
from Sweden as having blond hair and blue eyes-- those are both recessive
traits. Therefore, among the Swedish population, there tend to be a
majority of recessive alleles. Of course, not all Swedes are
blonde and blue-eyed!
| The version of a trait that can be
hidden. A recessive allele is only expressed when a person is
| Both alleles within one's genotype
for a specific gene are identical.
| The two alleles within one's
genotype for a specific gene are different. Keep in mind that we
have thousands of genes, and the genotype of each one can be described,
and some will be homozygous while others are heterozygous.