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Name_____________________________________
Class_____________________________________
Date______________________________________
Should This Dog Be Called Spot?
Imagine this microscopic drama. A sperm cell from a male dog fuses with an egg cell from a female dog. Each
dog’s gamete carries 39 chromosomes. The zygote that results from the fusion of the gamates contains 78
chromosomes-one set of 39 chromosomes from each parent. One pair of the zygote’s chromosomes are shown
below.
Each chromosome of the homologous pair contains alleles for the same traits. But one chromosome may have a
dominant allele and the other a recessive allele. Use the drawings and the table to answer the questions.
Trait
Hair length
Hair texture
Hair curliness
Coat pattern
Dominant Gene
Short (L)
Wiry (T)
Curly (H)
Spotted (A)
Recessive Gene
Long (l)
Silky (t)
Straight (h)
Solid (a)
Will the new puppy have a spotted coat? Explain. _____________________________________________
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Does the female dog have a spotted coat? Explain. _____________________________________________
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Does the male dog have a spotted coat? Explain. ______________________________________________
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What will be the texture of the puppy’s coat? __________________________________________________
Will the texture of the puppy’s coat resemble that of either of its parents? Explain. ___________________
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Will the puppy have curly hair or straight hair? ________________________________________________
a. Does the female dog have curly hair? ______________________________________________________
b. Does the male dog have curly hair? ______________________________________________________
a. Define the term heterozygous. ___________________________________________________________
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b. For which traits is the puppy heterozygous? ________________________________________________
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a. Define the term homozygous. ___________________________________________________________
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b. For which traits is the puppy homozygous? ________________________________________________
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Explain why you cannot completely describe the puppy’s parents even though you can accurately describe the
puppy. _____________________________________________________________________________
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Genetics Problems
Dihybrid Punnett Squares
Directions: On a separate sheet of paper, write the genotypes of the parents, use a punnett square to show your
work, and give the phenotypic ratio for each problem.
Key:
Brown eyes are dominant to blue
Dark hair is dominant to blonde hair
(B, b)
(H, h)
1. Mother: Brown eyed (homozygous)
Dark hair (heterozygous)
Father: Brown eyed (heterozygous)
Blonde hair (homozygous)
Mother: Blue eyes
Dark hair (homozygous)
Father:
Brown eyes (heterozygous)
Blonde hair (homozygous)
Mother: brown eyes (heterozygous)
dark hair (heterozygous)
Father:
SAME
Mother: brown eyes (heterozygous)
dark hair (heterozygous)
Father:
Blue eyes
dark hair (heterozygous)
KEY:
T tall pea plant
t dwarf pea plant
Y yellow pea seeds
y green pea seeds
Cross a tall (heterozygous), Yellow (homozygous)
with a
Dwarf (homozygous), Yellow (heterozygous)
Cross a tall (heterozygous), Yellow (heterozygous)
with
SAME
Cross a Dwarf (homozygous), Yellow (homozygous)
with a
Tall (heterozygous), Yellow (heterozygous)
Cross a Tall (homozygous), Green
with a
Dwarf, Yellow (heterozygous)
Cross a Dwarf, Green
with a
Tall (homozygous), Yellow (heterozygous)
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Genetics Problems
Incomplete Dominance
Incomplete dominance is the situation in which neither gene for a trait is dominant over the other; the two are
equally dominant. Mendel’s law of dominance does not apply in these cases because the offspring may not
resemble either parent. The appearance of the offspring is an intermediate between the contrasting traits of both
parents.
Directions: On a separate sheet of paper, write the genotypes of the parents, use a punnett square to show your
work, and give the phenotypic ratio of each problem.
KEY: RR = red coat color in cattle
rr = white coat color
Rr = roan coat color (brown)
1. Cross a white bull with a red cow
Cross a roan bull with a roan cow
In the next two cases only flower color is incompletely dominant. In the trait for height, tall is dominant to
dwarfness.
KEY: RR = red flowers
rr = white flowers
Rr = pink flowers
T = tall plant
t = dwarf plant
Cross a pink, tall (heterozygous) with a white, tall (heterozygous) flower
Cross a red, dwarf with a pink, tall (homozygous)
KEY: RR = red coat
rr = white coat
Rr = roan coat
H = horns
h = hornless
Using the key above, continue with problems 5-7
Cross a roan, hornless cow with a roan, horned (heterozygous) bull
Cross a roan, horned (heterozygous) with a roan, horned (heterozygous)
Cross a white, horned (homozygous) with a red, hornless
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Punnett Puzzlers
A.
Pure Gold?
Imagine that you have inherited a ranch filled with palomino horses. The palominos are golden in color with
blonde tails and manes. You decide to breed the palominos.
1. How could you determine if the palomino color displays incomplete dominance or a purebred trait (explain
an experiment to do this)?
Suppose that you bred many pairs of palomino horses and they produced these colts: 61 palomino, 32 brown,
and 29 white.
Do these results support the hypothesis that the palomino color is purebred? If not, what do the results support
(what type of inheritance)?
About what percentage of colts were palomino? Brown? White?
When the colts mature, you breed the brown horses together. All the resulting colts are brown. You also breed
the white horses together. All of their colts are white. Represent the genotype of brown horses as HBHB and
white HbHb. Complete the Punnett square to show the mating of two palomino horses.
B.
Cocker Spaniels
In cocker spaniel dogs, the genotype A-B-is black, aaB-is liver (brown), A-bb is red, and aabb is lemon colored.
A black cocker is mated with a lemon one and a lemon pup is born. If the same black dog is then mated with
another black dog of the same genotype, what colors of dogs might be produced and in what ratios?
C.
Deafness
In humans, the allele D is needed for a normal ear cochlea (inner ear structure) and the allele E is needed for a
normal auditory (ear) nerve. Without either of these genes the person is deaf. For example: Ddee=deaf,
ddEE=deaf.
1. Show the genotypes of 2 hearing parents who could have a deaf child.
Show the genotypes of 2 deaf parents who could have a hearing child.
D.
Mice
In mice, the genotype yy is gray, Yy is yellow, and YY is a lethal mutation where the baby mouse dies before
birth. What offspring could result from breeding a yellow mouse with a gray mouse? Give a phenotypic ration.
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E.
Cattle
In cattle, one pair of alleles, B and b, determine the color of cows. BB or Bb=black, bb=red. Another pair of
alleles determines how much color will be on the cattle’s body. RR=solid color, R’R’=no color (white), RR’ or
R’R’=spotted with white background. B is dominant; neither R nor R’ is dominant. If you mate a red and
white spotted cow (female) with a red and white spotted bull (male), what could the calves look like? List
genotypic and phenotypic ratios.
F.
The Hapsburgs
The Hapsburg family is notorious for having large lower lips.
1. Hank Hapsburg (Hh), married a girl who’s genotype is unknown. Their children have all three types of lips:
very large, slightly larger and normal size. What was Hank’s wife’s genotype?
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