Name
Class
Date
Genetics with a Smile
Smiley Faces are interesting creatures that are native only to Glenwood
Middle School and only be found there at certain times of the year. They are
good examples of mendelian genetics, which means that they have a
number of physical traits that are controlled by a single gene found on each
of a pair of chromosomes. For these genes, there are two versions, a
dominant version and a recessive version. These are different versions are
called alleles.
Define mendelian
genetics.
Part A: Parent Phenotypes
In this activity, two Smiley Faces are about to become parents. Both of these
parents happen to be heterozygous for all the “Smiley Face” traits, except
cleft chin. This means that one of the chromosomes in their chromosome
pair carries a dominant allele while the other carries a recessive allele. Even
though they carry a copy of the recessive allele, their appearance will anly
show the dominant allele. For the cleft chin gene, both parents are
homozygous dominant. These Smiley Face parents have two copies of the
dominant allele for the cleft chin gene.
Define heterozygous
and homozygous.
1. Determine the phenotypes for the mother and father using the genotypes
listed in the chart and information on Smiley Face traits on the following
page. You will complete the columns for the offspring later in the activity.
• CAPITAL LETTERS indicate a dominant allele.
• Lowercase letters indicate a recessive allele.
Part B: Gender of the Offspring
Humans have forty-six chromosomes arranged in twenty-three pairs. One of
these pairs includes the chromosomes that determine gender. These “sex
chromosomes” are commonly referred to as the X and Y chromosomes.
Females carry two copies of the X chromosome in each of their cells, so they
are XX. Males carry one X and one Y chromosome in their cells, so they are
XY. Since females have only copies of the X chromosome, each of their eggs
will carry a copy of one of their X chromosomes and they will always pass on
an X chromosome to their offspring. Since males carry an X and a Y, half of
their sperm will carry a copy of the X and half a copy of the Y. So the gender
of the offspring depends on which chromosome the father passes on.
2. Flip the coin once to see whether the Smiley Face father will pass on his X
or Y chromosome to his offspring in his sperm. Record your results in the
table. Heads will represent the first chromosome listed (in this case, the
X chromosome), while tails represents the second (the Y chromosome).
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Define chromosome.
Define offspring.
Define genotype.
Define phenotype.
Oelfke (elf-ka)
What is the genotype of the offspring? X
What is the phenotype of the offspring? (Is the baby Smiley Face a boy or
a girl?)
Part C: The Genotype of the Offspring
For every genetic trait, there are two genes, one on each of the
chromosomes in the pair an individual has. These genes affect that trait, but
are not necessarily identical to each other. The possible different versions of
the gene on each chromosome are called alleles. The parent’s gametes,
either the egg or sperm, will carry a copy of one of the alleles for that trait
from that parent’s chromosomes. An offspring will get one allele from the
pair the father has and one allele from the pair the mother has, so it ends up
with its own pair of alleles for every gene of its own. Which allele the
offspring will get from the pair that each parent has is completely random.
3. Flip the coin once for each parent, for each gene, to determine the
genotype. Record the result for each parent by circling the allele that will
be passed on (based on the coin flip). Then write both alleles in the chart
under the offspring genotype. Heads will indicate that the first allele
listed is copied into the gamete and passed on to the offspring. Tails will
indicate that the second allele is copied into the gamete and passed on
to the offspring.
• CAPITAL LETTERS indicate the Smiley Face offspring inherited a
dominant allele.
• Lowercase letters indicate the Smiley Face offspring inherited a
recessive allele.
Define allele.
Define dominant
allele.
Define recessive allele.
Part D: The Phenotype of the Offspring
4. Now that you have determined the genotype for the offspring, use the Smiley Face Traits chart to
determine the phenotype for each gene. Record your results on the chart under offspring
phenotype.
Part E: Create Your Smiley Face!
5. Using the phenotype you determined from part D and the Smiley Face Traits chart, create a sketch
of your Smiley Face on the back of this paper. Color your offspring according to its phenotype. If
you have extra time, give your Smiley Face a name and add a body and accessories.
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Oelfke (elf-ka)
Father
Trait
Mother
Genotype
Phenotype
(Physical
Appearance)
Genotype
Phenotype
(Physical
Appearance)
Sex
XY
Male
XX
Female
Face Shape
Gg
Gg
Eye Shape
Ee
Ee
Hair Style
Rr
Rr
Smile Style
Tt
Tt
Ear Style
Vv
Vv
Nose Style
Dd
Dd
Face Color
Yy
Yy
Eye Color
Bb
Bb
Hair Length
Ll
Ll
Freckles
Ff
Ff
Hair Color
Hh
Hh
Lip Color
Qq
Qq
Buck Teeth
Aa
Aa
Cleft Chin
PP
PP
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Offspring
Inherited Genotype
Allele from
Allele from
Father
Mother
Phenotype
(Physical
Appearance)
X
Oelfke (elf-ka)
Smiley Face Traits Key
Face Shape
Circle (G)
Eye Shape
Oval (g)
Star (E)
Smile Style
Thick (T)
Curved (V)
Face Color
Pointed (v)
Blue (B)
Freckles
Down (D)
Red (b)
Dark (H)
Dark (Q)
Light (q)
Cleft Chin
Yes (a)
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Short (l)
Lip Color
Light (h)
No (A)
Up (d)
Long (L)
Hair Color
Yes (f)
Curly (r)
Hair Length
Buckteeth
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Straight (R)
Nose Style
Eye Color
Green (y)
No (F)
Blast (e)
Ear Style
Thin (t)
Yellow (Y)
Hair Style
No cleft (P)
Cleft (p)
Oelfke (elf-ka)