Copyright © The Norwood Science Center 2005
The Norwood Science Center
Human Body
Grade 5
Background information:
The characteristics of an organism are called traits. The colors
of hair and eyes are examples of traits. Offspring inherit traits from
the genes passed on to them by their parents. Heredity is the
passing of traits from parents to offspring. Gregor Mendel may have
been the first person to study heredity. He lived in Austria during the
1800’s. Mendel learned about heredity by studying the traits of pea
plants.
Offspring are not exact copies of their parents. Some traits or
characteristics are dominant. These traits always appear when they
are inherited because dominant genes prevent another gene from
being expressed as a trait. Characteristics that are dominant, or
more likely to be passed on to children, are curly hair, dark hair, nonred hair, brown eyes, and short stature. Other traits are recessive.
Characteristics that are recessive, or less likely to be inherited, are
straight hair, light color hair, red hair, blue or gray eyes, and tall
stature. When these recessive genes are inherited, a dominant gene
can hide them. The only time a recessive gene is expressed as a
trait is when the genes from both parents are recessive. For
example, no dominant genes are present when both parents have
blue eyes.
Brown hair in mice is a dominant trait. White hair is a recessive
trait. If a mouse inherited the brown trait from both parents, it will be
brown. If it inherits the brown hair trait from one parent and the white
hair trait from the other, it will still be brown. But the trait for white
hair is not lost. It is just hidden. It can be passed on to the next
generation. A mouse will only be white if it inherits the trait for white
hair from both parents. This study of inherited traits is called
genetics.
There are times when we cannot call a trait dominant or
recessive. Two traits may blend or mix together in the offspring. For
What Traits Are Most Common Gr. 5 07
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example, four-o’clocks are flowers that may be red or white. The
gene for red flowers is not dominant or recessive. The gene for white
flowers is not dominant or recessive either. If a red four-o’clock is
crossed with a white four-o’clock, the offspring are pink. There are
many human traits that act in the same way. Height is one of those
traits.
In this lesson, students will determine the presence of the
following dominant traits: tongue-rolling; PTC taster; dimples; free
ear lobes; and brown eyes.
TITLE:
WHAT TRAITS ARE MOST COMMON?
PURPOSE:
Make frequency tables of the number of students
with certain inherited physical traits
Determine the presence of a dominant trait
MATERIALS:
(per student)
Comparing Traits worksheet
PROCEDURE:
01. Explain to students that they will be finding out something about
the common traits in the class.
02.
Distribute worksheet to each student.
Tongue-rolling:
03. Some people can roll their tongues into a U-shape (see Figure
1 on last page). Tongue rolling is a dominant trait. Not being
able to roll the tongue is a recessive trait. Each member of the
class should determine if they can roll their tongue into a Ushape.
04.
Count the number of students that can roll their tongues and
have students place this value in the appropriate column of the
worksheet. Count the number of students that cannot roll their
tongues and place this value in the appropriate column of the
worksheet.
PTC Taster:
What Traits Are Most Common Gr. 5 07
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05.
In a previous Science Center lesson, students were given some
paper that had been dipped in a chemical called PTC. Being
able to taste PTC is a dominant trait. Not being able to taste
PTC is a recessive trait.
06.
Count the number of students that were able to taste PTC and
have students write this value in the appropriate column of the
worksheet. Count the number of students that could not taste
the PTC and place this value in the appropriate column of the
worksheet.
Dimples:
07. Dimples are small, slight hollows formed in the act of smiling.
Having dimples is a dominant trait. Not having dimples is a
recessive trait. Each member of the class should determine if
they have dimples.
08.
Count the number of students that have dimples and have
students place this value in the appropriate column of the
worksheet. Count the number of students that do not have
dimples and place this value in the appropriate column of the
worksheet.
Free ear lobe:
09. Some people have free ear lobes (see Figure 2 on last page).
Free ear lobes is a dominant trait. Attached ear lobes is a
recessive trait. Each member of the class should determine if
they have free or attached ear lobes.
10.
Count the number of students that have free ear lobes and
have students place this value in the appropriate column of the
worksheet. Count the number of students that have attached
ear lobes and place this value in the appropriate column of the
worksheet.
What Traits Are Most Common Gr. 5 07
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Brown eye color
11. Brown eye color is a dominant trait. Non-brown eye color is a
recessive trait. Each member of the class should determine if
they have brown eye color or non-brown eye color.
12.
Count the number of students that have brown eyes and have
students place this value in the appropriate column of the
worksheet. Count the number of students that have non-brown
eyes and place this value in the appropriate column of the
worksheet.
CONCLUSION:
Discuss the following questions with the class and have students
write the answers in their notebooks:
01.
Which dominant traits are common in your class?
02.
Which recessive traits are common in your class?
03.
Why do you think some dominant traits are not common?
04.
If you studied another classroom of people, how do you think
your results would be different?
SOURCE:
01.
02.
03.
Life: Activities and Explorations, Houghton Mifflin, Boston, 1975.
Accent on Science, Merrill, Columbus OH, 1983.
Bones, Bodies, and Bellies. GoodYear Books, Glenview, IL, 1994.
What Traits Are Most Common Gr. 5 07
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Name ______________________
Date _________________
Comparing Traits
Dominant
trait
Number of
people
Recessive
trait
Can roll tongue
into U-Shape
Cannot roll
tongue into Ushape
Curly hair
Straight hair
Dimples
No dimples
Free ear lobe
Attached ear
lobe
Brown eyes
Non-brown eyes
What Traits Are Most Common Gr. 5 07
Number of
people
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Figure 1
Figure 2
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