Human Characteristics
Practicing forming genotypes and determining the phenotypes
As you know, chromosomes work in pairs. The members of each chromosome pair are
called homologous chromsomes, and the two chromosomes of each pair are approximately the
same length, the same shape and carry alleles for the same genes. Each chromosome of a pair
comes from a different parent: one from the mother through the egg and the other from the
father through the sperm. At fertilization those like chromosomes pair up to form the
homologous pairs in YOU. Humans have 23 pairs of chromosomes, or a total of 46
chromosomes, per cell. Chromosomes 1-22 are called autosomes and the 23rd are the sex
chromosomes. Only 22 of these pairs are truly homologous since, for males, the 23 rd pair is XY.
The diagram below shows a generalization view of one pair of homologous
chromosomes from an individual human. Assume that chromosome on the left is from the
father and the one on the right is from the father (ladies first!).
Example:
From mom
---------------
From dad
F Freckled
T can taste
H Widow’s peak
D no disease
Rh+
M dimples
e attached lobe
The genotypes and corresponding
phenotypes of the person above are:
Genotypes
Ff
Tt
Hh
DD
Rh+ RhMm
ee
Phenotypes
Freckled
taste ability
Widow’s peak
has the disease
makes the protein
dimples
attached earlobes
---------------
Characteristics
f unfreckled
Freckled skin
t cannot taste
h straight hairline
D has disease
chemical taste ability
has a widow’s peak
presence of a disease
Rhm no dimples
e attached lobe
Rh blood factor
dimples
attached earlobe
Analyze the information:
1. Which parent gave the allele for straight hairline? DAD
2. Did that parent have a straight hairline? POSSIBLY if he was Hh
3. Does this person have a straight hairline? NO
4. Does this person have the recessive trait attached earlobes? YES
5. If both parents have unattached earlobes, why does this person
have attached? BOTH must be Ee and each gave the ‘e’ to the child
Sample I: Jill
From Mom From Dad Genotypes
1_____
______________________________________
2 _____
______________________________________
3 _____
______________________________________
4 _____
______________________________________
Rh+
5_____
______________________________________
m
E
6_____
______________________________________
7_____
______________________________________
F
t
H
d
f
t
h
d
Rh+
m
e
I.
Sample II: Tammy
From Mom From Dad Genotypes
F
T
h
d
f
T
h
d
+
Rh
m
E
Phenotypes
Rh-
m
e
I.
Phenotypes
1_____
______________________________________
2 _____
______________________________________
3 _____
______________________________________
4 _____
______________________________________
5_____
______________________________________
6_____
______________________________________
7_____
______________________________________
Sample III: Nancy
From Mom From Dad Genotypes
f
t
H
d
f
t
H
D
Rh-
Rh-
M
e
M
e
I.
Phenotypes
1_____
______________________________________
2 _____
______________________________________
3 _____
______________________________________
4 _____
______________________________________
5_____
______________________________________
6_____
______________________________________
7_____
______________________________________
Analysis: Remember, some of your answers maybe “possibly,” then give the “if
scenario.”
 Was Jill’s father freckled?
 Was Jill’s mom freckled?
 Did either of Jill’s parents have the ability to taste?
 Are all of Tammy’s brothers and sisters have unattached earlobes?
 When Tammy has kids, will they have unattached earlobes?
 Does Nancy produce the Rh protein?
 Did both of her parents?