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Copyright © The Norwood Science Center 2005
The Norwood Science Center
Human Body
Grade 5
TITLE:
GENETICS OF EYE COLOR
PURPOSE:
How is eye color passed on from parents to
offspring?
MATERIALS:
(per student)
Notebook
Pencil
Punnett Square Worksheet
(per teacher)
Overheads reviewing Intro to Genetics lesson and
Punnett Square worksheet
PROCEDURE:
01.
Allow students 5 minutes to review their notes from the
Introduction to Genetics lesson presented during their last
Science Center visit.
02.
Using overheads (see attached) students are presented with a
series of statements in Jeopardy Game fashion. Their task is to
prepare a question that correctly addresses the statement. This
step serves as a reinforcement of the previous lesson and an
introduction to the current lesson.
03.
Review with students the following previously presented
concepts from the Intro to Genetics lesson:
 Genes contain a set of directions for a trait.
 Genes appear in pairs – one passed on from each parent.
 There are two types of genes – Dominant and recessive.
 Dominant genes carry a trait that always appears if inherited.
 Recessive genes carry a trait that will be masked over if
paired with a Dominant gene.
 Upper case letters are used for Dominant traits while lower
case letters are used for recessive traits.
Genetics of Eye Color Gr. 5 07
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Copyright © The Norwood Science Center 2005
04.
Having Freckles is a Dominant trait and is designated with the
upper case letter “F.” Not having Freckles is a recessive trait
and is designated with the lower case letter “f.”
05.
Provide the class with the following chart on the board:
Individual #1
Individual #2
Individual #3
Gene Pair
FF
Ff
ff
Individual #1 will have Freckles since they are completely
Dominant for the trait. Individual #2 will also have Freckles
since the Dominant “F” gene will mask over the recessive “f”
gene. Individual #3 will not have Freckles since they are
completely recessive for the trait and do not possess the
Dominant gene for Freckles.
06.
Write the following terms and definitions on the board:
 Genotype – the type of genes you have
 Phenotype – the trait shown or displayed based on your
genotype
07.
Display the following chart on the board and ask students to
complete the missing information:
Individual #1
Individual #2
Individual #3
Genotype
FF = Dominant/Dominant
?
?
Phenotype
Freckles
?
?
Genotype
FF = Dominant/Dominant
Ff = Dominant/recessive
Ff = recessive/recessive
Phenotype
Freckles
Freckles
no Freckles
Solution:
Individual #1
Individual #2
Individual #3
Genetics of Eye Color Gr. 5 07
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Copyright © The Norwood Science Center 2005
08.
Distribute a copy of the Punnett Square worksheet to each
student.
09.
The Punnett Squares will be used to determine the four
possible outcomes of gene pairs of offspring based on the gene
pairs of the parents. The trait discussed will be eye color –
specifically the Dominant eye color Brown (B) and the recessive
eye color blue (b).
10.
Using the first Punnett Square, have students write in the
following gene pairs of parents who genotype is
Dominant/Dominant and phenotype is brown eyes:
B
B
B
B
11.
Offspring receive one gene from each parent. If the offspring
received one Brown eye gene from one parent and another
Brown eye gene from the other parent, one resulting gene pair
for the offspring would be BB as indicated below.
B
B
B
BB
B
Genetics of Eye Color Gr. 5 07
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Copyright © The Norwood Science Center 2005
12.
Completion of the Punnett Square and calculation of the
occurrences of the four types of gene pairs would indicate the
following possibilities for offspring of two parents completely
Dominant for Brown eyes:
B B
B BB BB
B BB BB
BB = 4/4 = 100%
Bb = 0/4 = 0%
bB = 0/4 = 0%
bb = 0/4 = 0%
All the offspring will be completely Dominant for Brown eyes.
12. In the next Punnett Square, students are instructed to write in
the following genotypes for parents and are guided through the
process of completing the sections of the Punnett Square and
the calculating of the occurrences of the four types of gene
pairs.
B
b
B BB Bb
b
Bb bb
BB = 1/4 = 25%
Bb = 1/4 = 25%
bB = 1/4 = 25%
bb = 1/4 = 25%
CONCLUSION:
01. Ask the class, could two brown-eyed parents have a blue eye
child? From their data, they will notice that there is a 25%
chance of two brown-eyed parents having a blue-eyed child as
long as both parents carry the recessive gene for blue eyes and
pass that gene along to their offspring.
02.
It should be clear from their Punnett Square calculations that in
order for a recessive trait to appear, the gene pair for that
individual must be completely recessive. If the Dominant gene
did occur, it would mask over the recessive trait and not allow it
to be displayed.
Genetics of Eye Color Gr. 5 07
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