Copyright © 2007 Stevens Institute of Technology
Center for Innovation in Engineering and Science Education
Goal
Determine if the dominant trait is the most
prevalent trait
•What is a trait?
•What is a dominant trait?
•What does it mean to be most prevalent?
Copyright © 2007 Stevens Institute of Technology
Center for Innovation in Engineering and Science Education
What is a trait?
• Genetically determined characteristic
• What does ‘genetically determined’ mean?
• Whatever was passed on to you from your
parents
• This determines how you will look.
Copyright © 2007 Stevens Institute of Technology
Center for Innovation in Engineering and Science Education
What is a trait?
• More specifically, it is all the instructions
your parents gave you so that you could
actually make yourself!
• Your Mom gives you ½ of the instructions,
your Dad gives you the other ½.
• How can you tell?
Copyright © 2007 Stevens Institute of Technology
Center for Innovation in Engineering and Science Education
What is a trait?
• “Your Mom gives you ½ of the instructions,
your Dad gives you the other ½.”
• In science jargon: Your Mom gives you
one allele of that gene and your Dad gives
you one allele of that gene and you put
them together to make a chromosome.
Copyright © 2007 Stevens Institute of Technology
Center for Innovation in Engineering and Science Education
Where does this happen?
• The DNA or genes in the nucleus of the
cell contains the building instructions
• Those instructions are copied and carried
outside the nucleus where they will act
Copyright © 2007 Stevens Institute of Technology
Center for Innovation in Engineering and Science Education
• What instructions or genes you have from your
parents are said to be your genotype
• What people see on the outside is your
phenotype
• So your genotype determines your phenotype!
Copyright © 2007 Stevens Institute of Technology
Center for Innovation in Engineering and Science Education
What are dominant traits?
• When alleles get together, some alleles are
“stronger” than other alleles.
• We call these alleles dominant and then the trait
that they express the dominant trait.
• Both parents might give you instructions on how
your ear lobes will look, but some looks are
dominant (stronger) than others
• Let’s try a simulation…
Copyright © 2007 Stevens Institute of Technology
Center for Innovation in Engineering and Science Education
Ear lobes
• Free earlobes (dominant
trait) hang below the point of
attachment to the head.
• Attached ear lobes
(recessive trait) are attached
directly to the side of the
head.
Copyright © 2007 Stevens Institute of Technology
Center for Innovation in Engineering and Science Education
Prevalent
• The trait that we see mostly when we look
around at people is the prevalent trait.
• If more people have attached ear lobes
then that is the most prevalent.
Copyright © 2007 Stevens Institute of Technology
Center for Innovation in Engineering and Science Education
The physical characteristics below are
common genetic traits inherited from
one generation to the next:
 Free vs. Attached Earlobes
 Straight vs. Curved Thumbs
 Bent vs. Straight Pinky
 With vs. Without White Forelock
Copyright © 2007 Stevens Institute of Technology
Center for Innovation in Engineering and Science Education
Thumbs
• Straight thumbs (dominant
trait) can be seen as nearly a
straight line and may contain
a slight arch when viewed
from the side as in the
illustrations.
• Curved thumbs (recessive
trait) can be seen as part of
a circle.
Copyright © 2007 Stevens Institute of Technology
Center for Innovation in Engineering and Science Education
Pinky
Bent pinky (dominant trait)
vs. Straight pinky
(recessive trait):
1. Hold your hands together as if
you are covering your face.
2. If the tips of the pinkies (or
baby fingers) point away from
one another, the pinkies are
bent (recessive trait).
Copyright © 2007 Stevens Institute of Technology
Center for Innovation in Engineering and Science Education
Forelock
• A White Forelock (dominant
trait) is a patch of white hair,
usually located at the hairline
just above the forehead. The
photo to the left clearly shows
an exaggerated white
forelock.
• No White Forelock is the
recessive trait.
Copyright © 2007 Stevens Institute of Technology
Center for Innovation in Engineering and Science Education
• For a given trait, which expression
(dominant or recessive) would you expect
to be most prevalent?
• Is that true?
• How can we really be sure?
Copyright © 2007 Stevens Institute of Technology
Center for Innovation in Engineering and Science Education