Gregor Mendel used pea plants to study heredity in a series of experiments. Mendel worked by carefully observing and recording traits in successive generations of plants. Knowledge about DNA and chromosomes came later. This lab will apply genetic laws to human inheritance using Punnett squares. Recall that DNA is wound tightly into chromosomes. Cells with only one set of chromosomes, such as sex cells, are  haploid . When two haploid cells fuse during fertilization, a diploid zygote with two full sets of chromosomes is formed. Most cells of a mature individual are diploid. Homologous chromosomes  have the same genes, but they might have different versions ( alleles ) of those genes.  Diploid  cells have two alleles for each gene. These alleles might be identical (gene A) or different (gene B). Each gene’s  locus  is its location on a chromosome. Human traits come through dominant or recessive inheritance. For example, the cystic fibrosis traits carried by a dominant allele are always expressed, even if the recessive gene is present (FF or Ff). The recessive is only expressed when two copies of the recessive allele are present (ff). Mother: Healthy carrier F f Father: Healthy carrier F FF Healthy non-carrier Ff Healthy carrier f Ff Healthy carrier FF Affected Human gender is carried on the X and Y chromosomes. Females are XX and males are XY. Heredity traits such as color blindness, which is the inability to distinguish among some colors, are carried on the X chromosome (X c ). The presence of one normal X C  will allow normal vision. In this next set of exercises, you will determine the genotypes of the parents by considering the inheritance patterns of traits in their children. The following is a table of the phenotypes of the family members: Phenotype Alleles Parents Mother Not color blind Freckles Type B blood X c  X C Ff I B i Father Color blind No freckles Type A blood X c Y Ff I A i Children Abby Color blind Freckles X c  X c Ff or ff Brady Not color blind No freckles X C Y ff Carly Not color blind No freckles X c  X C ff Dennis Color blind Freckles X c Y Ff or ff Exercise 1: Color Blindness Using the alleles XC (not color blind) and Xc (color blind), distribute the gametes from each parent to the outside of the Punnett square. Drag and drop the child with the correct phenotype to the box within the Punnett square that has the corresponding genotype that would occur from the fusion of egg and sperm as indicated by your placement of the gametes. Exercise 2: Freckles Freckles are groups of cells on the skin that produce the pigment melanin, often in response to exposure to ultraviolet (UV) light. The gene for freckles is inherited in a dominant/recessive pattern. A person carrying even a single copy of the dominant allele (F) will have freckles. A person who is homozygous recessive (ff) will have no freckles. Using the alleles F (freckles) and f (no freckles), distribute the gametes from each parent to the outside of the Punne.

1. Gregor Mendel used pea plants to study heredity in a series of
experiments. Mendel worked by carefully observing and
recording traits in successive generations of plants. Knowledge
about DNA and chromosomes came later.
This lab will apply genetic laws to human inheritance using
Punnett squares.
Recall that DNA is wound tightly into chromosomes. Cells with
only one set of chromosomes, such as sex cells, are
haploid
. When two haploid cells fuse during fertilization, a diploid
zygote with two full sets of chromosomes is formed. Most cells
of a mature individual are diploid.
Homologous chromosomes
have the same genes, but they might have different versions (
alleles
) of those genes.
Diploid
cells have two alleles for each gene. These alleles might be
identical (gene A) or different (gene B). Each gene’s
locus
is its location on a chromosome.
Human traits come through dominant or recessive inheritance.
For example, the cystic fibrosis traits carried by a dominant
allele are always expressed, even if the recessive gene is present
(FF or Ff). The recessive is only expressed when two copies of
the recessive allele are present (ff).
Mother: Healthy carrier
F
f

2. Father: Healthy carrier
F
FF
Healthy non-carrier
Ff
Healthy carrier
f
Ff
Healthy carrier
FF
Affected
Human gender is carried on the X and Y chromosomes. Females
are XX and males are XY. Heredity traits such as color
blindness, which is the inability to distinguish among some
colors, are carried on the X chromosome (X
c
). The presence of one normal X
C
will allow normal vision.
In this next set of exercises, you will determine the genotypes
of the parents by considering the inheritance patterns of traits in
their children. The following is a table of the phenotypes of the
family members:
Phenotype
Alleles
Parents
Mother
Not color blind
Freckles
Type B blood
X
c
X

3. C
Ff
I
B
i
Father
Color blind
No freckles
Type A blood
X
c
Y
Ff
I
A
i
Children
Abby
Color blind
Freckles
X
c
X
c
Ff or ff
Brady
Not color blind
No freckles
X
C
Y
ff
Carly
Not color blind

4. No freckles
X
c
X
C
ff
Dennis
Color blind
Freckles
X
c
Y
Ff or ff
Exercise 1: Color Blindness
Using the alleles XC (not color blind) and Xc (color blind),
distribute the gametes from each parent to the outside of the
Punnett square. Drag and drop the child with the correct
phenotype to the box within the Punnett square that has the
corresponding genotype that would occur from the fusion of egg
and sperm as indicated by your placement of the gametes.
Exercise 2: Freckles
Freckles are groups of cells on the skin that produce the
pigment melanin, often in response to exposure to ultraviolet
(UV) light. The gene for freckles is inherited in a
dominant/recessive pattern. A person carrying even a single
copy of the dominant allele (F) will have freckles. A person
who is homozygous recessive (ff) will have no freckles.
Using the alleles F (freckles) and f (no freckles), distribute the
gametes from each parent to the outside of the Punnett square.
Drag and drop the child with the correct phenotype to the box
within the Punnett square that has the corresponding genotype
that would occur from the fusion of egg and sperm as indicated
by your placement of the gametes.
Exercise 3: Blood Type

5. In
codominance
, more than one allele encodes a functional protein. IA codes for
A markers on red blood cells. IB codes for B markers. i codes
for neither A nor B markers, no markers. Human blood types
IAIA and IAi are Type A blood. IBIB and IBi are Type B blood.
IAIB is a codominant expression of alleles and results in type
AB blood. ii is Type O blood.
Genotypes
Phenotypes
I
A
I
A
or
I
A
i
Blood Type A
I
B
I
B
or
I
B
i
Blood Type B
I
A
I
B
Blood Type AB
ii
Blood Type O
These parents have a child with Type O (ii) blood. Investigate

6. the possible genotypes for each parent to determine how this
genetic outcome would occur. Why must each parent carry the i
allele to have a child with Type O blood? Drag and drop the
gametes from each parent to the outside of the Punnett square.
Drag and drop the corresponding zygote to each block of the
Punnett square.
Reference
Audesirk, T., Audesirk, G., & Byers, B. E. (2008).
Biology: Life on earth with physiology
. Upper Saddle River, NJ: Prentice Hall.M