UNIT
4: LESSON 2
GENES-R-US
SUBJECT:
Science
OBJECTIVE:Students
will learn that genes they inherited from their parents determined some
of their traits.
MEASUREMENT:
Students will know that genes determined some of their traits.
BACKGROUND FOR
TEACHERS:
During the 1860s,
an Austrian monk and botanist named Gregor Mendel discovered that "factors"
determine inheritance in pea plants. He observed that many traits, from
height to flower color, seemed to be controlled by these factors. In
1903, researcher William Sutton made the connection between Mendel's
factors and chromosomes-microscopic structures in the cell nucleus that
carry genetic material. The genetic material itself, known as deoxyribonucleic
acid (DNA), was discovered by Johann Miescher in Switzerland in 1869.
Yet it wasn't until two researchers, Francis Crick and James Watson,
proposed a double-helix structure for the molecule that we began to
understand how this material carries the genetic code of life.
A gene is a unit
of information that can be passed on to offspring. It is a segment of
DNA. Genes help determine whether your hair is straight, whether your
eyes are brown, and whether you can curl your tongue. They also may
help determine whether you'll get a certain disease, have a learning
disability, or be a gymnastics champion. Genes are powerful influences
on physical and mental characteristics. Yet genes don't exist only in
people. Genes make hens white or speckled, give frogs smooth skin and
let roses smell sweet.
They influence all
the traits of corn covered in Unit 4, Lesson 1.
Genes are found in all living things!
As mighty as genes
are, however, it's important to remember that environment also helps
shape organisms. A person might have a genetic predisposition to be
tall, yet be short because of poor childhood diet. A plant might inherit
a tendency to produce bright red blooms, but be unable to flower because
of lack of nutrients. (Nutrients needed for corn are discussed in Unit
2, Lesson 2.) The interactions between a living thing and its environment
affect how it will turn out.
Domineering Genes
With some exceptions,
every organism has two of each kind of gene. An offspring gets one of
each type from each parent. Genes are usually either dominant or recessive.
A dominant gene is expressed in the offspring no matter what gene the
other parent contributes. A recessive gene is expressed in the offspring
only if both parents contribute recessive genes. If you have blue eyes,
both of your parents contributed a recessive blue gene. And yes, it
is possible for two brown-eye parents to have blue-eyed children, if
both contribute the recessive blue-eyed gene.
Mutations Rule
Over the billions
of years the earth has been around, plants, animals and other living
things, have evolved through the changing of genes. Genes have been
transferred, deleted and mutated between generations. These changes
led to life as we know it today.
Mutation produced
the countless variations of living things we see around us. Most mutations
place a living thing at a disadvantage-for example, a mutation might
produce a white caterpillar that is easily spied by predators. Some
mutations, however, give an individual a better chance of survival.
Individuals with such mutations are more likely to survive to have offspring,
so over time, this mutant gene will likely become established in the
gene pool (the genes of a breeding population).
Genes Across
the Ages
In nature, genes
generally are transferred between members of the same species. Some
new studies, however, suggest that genes also move between unrelated
organisms. For the most part, such "horizontal" gene transfer takes
place between bacteria and viruses.
Today, horizontal
gene transfer also can occur through genetic engineering (See Unit 4,
Lesson 4), tools of the new biotechnology that came into existence during
the 1970s. DNA can be transferred via direct injection or by inserting
the DNA into bacteria or viruses that carry it into the cells they infect.
This means that traits determined by single genes can conceivably be
transferred from one living thing to another.
Characteristics
coded for by more than one gene are much harder to transfer, since the
contributing genes must all first be identified, found, and isolated.
The idea of moving genetic material from one living thing to another
will continue to challenge researchers well into the 21st century.
STUDENT ACTIVITIES:
1. Ask students
to read the story Elizabeth Learns Why She Has
Blue Eyes, paying close attention to the features she inherited
from her mom and dad-blue eyes, height, hair, teeth, brains!
2. Complete the
activity described on the following worksheet. (Worksheet 1) In this
activity, pipe cleaners will represent genes that control certain traits.
The traits were chosen as examples because these traits are coded as
single genes in people. Many human characteristics such as height or
weight are coded by multiple genes. (Example 1, 2)
There will be 10
bags, 5 representing "Mom's genes" and 5 representing "Dad's genes."
The number of pipe cleaners in each bag should equal or exceed the number
of participants.
Acknowledgements:
The material in
this section was derived from the book Field of Dreams: Making Sense
of Biotechnology in Agriculture, published by the National 4-H Council.
(Found on the Internet at http://www.fourhcouncil.edu).
