Download Key to Reebop Traits

Name
Period
INTRODUCTION
SAMPLE CHROMOSOMES
As you know from your studies in genetics, chromosomes work
in pairs. The members of each pair of chromosomes are called
homologous chromosomes and are approximately the same
length and 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. Humans have 23 pairs of chromosomes, or
a total of 46 chromosomes per cell. Only 22 of these pairs are
truly homologous. The twenty-third pair, the sex chromosomes,
may or may not match, depending on whether the individual is
female (XX) or male (XY).
Father
The diagram to the rights shows a
generalized view of one pair of
homologous chromosomes from an
individual
human.
The
two
chromosomes are the same shape
and size, and carry alleles for the
same genes at equivalent positions.
Assume the chromosome on the left
is from the father and the one on the
right is from the mother.
You should be aware that any two alleles of a gene have
different effects on the trait that they control. For example, the
M allele causes more melanin to be made in the skin, giving a
darker color; the m allele causes less melanin, resulting in
lighter colored skin. Even though the effects are different, the
two alleles in an allele pair control the same trait  in this case
skin color.
Mother
Date
Characteristic
F  freckled
f  unfreckled
Freckled skin
T  can taste
t  can’t taste
Ability to taste bitter
B  brown
b  blond
Hair color
h  no disease
H  has disease
Genetic disease
Rh+
Rh -
Rh blood factor
(+ is dominant)
M  more
m  less
Melanin skin color
c  color blind
C  color vision
Color perception
Determine the genotypes and phenotypes of the person
whose chromosomes are shown above.
Trait
Having freckles
Ability to taste bitter
Hair color
Genetic disease
Rh blood factor
Skin color
Color vision
Genotype Phenotype
ACTIVITY
Father
Determine the genotypes and phenotypes of the people
whose chromosomes appear below.

Then answer the questions that follow about them and their
families.
Juanita

Mother
f
F
t
t
b
B
h
h
Rh+
Rh+
m
m
C
C
Genotype
Phenotype
Ff
freckled
f
F
T
T
b
b
h
h
Rh-
Rh-
m
m
C
c
Father
Phil
Dave
Father
Mother
Mother
f
f
t
t
B
B
h
H
Rh-
Rh-
M
M
c
c
Genotype
Phenotype
Genotype
Phenotype
QUESTIONS
In some cases where the child inherited a recessive allele, you
may not have enough information to answer the question 
Check NEI for “Not enough information”
YES
NO
ANALYSIS
1. Would Juanita like the taste of baker’s chocolate? Explain
why or why not genetically.
NEI
1. Was Dave’s mother freckled?
  
2. Was Dave’s father freckled?
  
3. Does FF show more freckles than Ff?
  
4. Were either of Dave’s parents
tasters?
  
5. Are all of Juanita’s brothers and
sisters blond?
  
6. When Juanita has children of her
own, will they be tasters?
  
7. Do Juanita’s parents have a genetic
disease?
  
8. Is Phil’s hair dark?
  
9. Do Dave’s parents have a positive (+)
blood type?
  
10. Were both of Phil’s parents colorblind?
  
2. Color-blindness is a recessive trait associated with the X
chromosome of the 23rd pair. Why are males more likely to
show the color-blindness trait than females?
3. In this lab, “M” stands for the occurrence of melanin. How
can you account for all the variations in skin color if “M” is
dominant over “m”?