Lab 11 – Genetics ConceptsSection II:
The following is a four-step method of organizing the results of a genetic cross. A
Punnett square is used to show all possible gene combinations in a particular gene
cross.
Step 1 Segregate the parental alleles into gametes
Parents (diploid): purple flowers AA X white flowers aa
Gametes (haploid):
A
A
a
a
Step 2 Position the gametes of the purple flowered plant horizontally
along the top of the Punnett square. Position the gametes of the white
flowered plant along the vertical side of the Punnett square. Record in
Lab Report.
Step 3 Predict all possible combinations these two sets of gametes could
produce by pairing a letter from the top of the box with one along the side.
Write the pair of letters inside of the box. A pair of letters inside a box
represents a diploid offspring. The dominant allele (capital letter) is
written first.
A
A
a
Aa
Aa
a
Aa
Aa
Step 4 Determine the genotype and phenotype of the offspring and in
what proportion of the offspring they can be found.
Percentage
Ratio
Phenotype: purple flowers
100%
4:0
Genotype: Aa
100%
4:0
EXERCISE 2 Predict the possible offspring of a cross between two
heterozygous purple flowered plants
Purple flower Aa X Purple flower Aa
Step 1 Identify the parental genotypes and phenotypes and the types of
alleles possible in the gametes. Record in Lab Report.
Step 2 Position the gametes from one parent along the top of the Punnett
square below. Position the gametes from the other parent along the left
side of the Punnett square below. Record in Lab Report.
Step 3 Predict all of the possible offspring produced by pairing an allele
from the top of the box with one along the side of the box. Write the pair
of alleles inside the box. A pair of alleles inside a box represents a diploid
offspring. Always write the capital letter (dominant allele) before the
lower case letter (recessive allele).
Step 4 Determine the phenotype and genotype of the offspring and the
proportions in which each will occur. Record in Lab Report.
Section IV:
EXERCISE 7 Gamete formation in a dihybrid cross
To determine the possible gene combinations in the gametes, select an
allele from one of the gene pairs and match it with an allele from the other
gene pair.
AaTt = AT
AaTt = At
AaTt = aT
AaTt = at
Note that the gametes contain two different letters representing two
different traits. Each letter symbolizes the single copy of the allele that is
present in the gamete.
•
List all possible gametes which can be produced by an AATT pea
plant in Lab Report.
Parental Genotype (diploid):
Meiosis
Gamete Genotype (haploid):
AATT
Repeat for all four gametes
AT AT AT AT
During fertilization, two haploid gametes fuse and the diploid condition is
restored.
Note: place the letters which represent the same trait back together, the
capital letter first, when you write the resulting offspring’s genotype
AATt, etc.
EXERCISE 8 Predict the offspring of a dihybrid cross in peas
Punnett squares can be used to predict the outcome of dihybrid crosses just
as they are used to predict the outcome of monohybrid crosses.
In pea plants, the allele for purple flowers is dominant over the
allele for white flowers, and the allele for tall plants is dominant
over the allele for dwarf plants.
Trait 1 flower color, A = purple, a = white
Trait 2 plant height, T = tall,
t = dwarf
Step 1 Cross two individuals who are heterozygous for both flower
color and plant height. Record in Lab Report.
Step 2 Each parent produces four types of gametes, 16 boxes are
needed in the Punnett square to account for all possible types of
offspring. Position the gametes from one parent along the top of the
Punnett square pictured below. Position the gametes from the other
parent along the side of the Punnett square. Record in Lab Report.
Step 3 Predict all possible types of offspring these two sets of gametes
could produce by pairing a set of letters from the top of the box with a set
along the side of the box. Write the four letters representing the
offspring’s genotype inside the box. Place the letters which represent the
same trait back together when you fill in the boxes (AATt, etc.).
Step 4 Record the phenotypes from the above cross and their ratio in
Lab Report.
EXERCISE 9 Predicted and actual results of a dihybrid cross in corn
In corn, purple kernels are dominant over yellow kernels, and round
kernels are dominant over wrinkled kernels. Corn kernels with starchy
endosperm are round, while those with a sweet endosperm are wrinkled.
Trait 1 kernel color, purple = A, yellow = a
Trait 2 kernel shape, round = R, wrinkled = r
Complete Cross 1-3 in your Lab Report.
Cross 1 Cross two corn plants, one homozygous dominant AARR and
one homozygous recessive aarr.
Cross 2 Cross two heterozygous AaRr corn plants and predict their
possible offspring.
Cross 3 Examine the corn sample demonstrating a dihybrid cross. Notice
that the kernels are two different colors (trait 1) and that the kernels are
two different shapes (trait 2).
BioLab3
Genetic Concepts Lab Report
Name, date, course and section required for password:
The lab report is unique each semester and checks have been put into place to ensure students
are doing their own work. Copying from other students or from outside resources will result in a
zero on the accompanying lab quiz.
I. Meiosis and Inheritance
1. What is a Punnett square?
2. Give an example of a genotype and a phenotype.
3. What is the difference between homozygous and heterozygous?
II. Mendel’s Experiments
1. An individual expresses a trait with the alleles Gg. Is this genotype homozygous
dominant, homozygous recessive, or heterozygous?
2. Complete the following Punnett square:
D
D
d
d
3. In the Punnett square above, what percent of the offspring are heterozygous?
4. Refer to Lab Exercise 3, Cross 1. What are the genotypes of the offspring between
the homozygous purple plant and the homozygous yellow plant?
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5. Refer to Lab Exercise 4. Count all kernels on all rows of the F2 corn and record the
number of purple kernels and the number of yellow kernels. Then record the
approximate, simplified ratio of purple to yellow.
Purple kernels
Yellow kernels
Ratio of
purple:yellow
6. Refer to Lab Exercise 5. What genotype of the black-furred males, BB or Bb, will
ensure all black furred offspring?
7. Use the test cross below to show how all black furred offspring can be produced.
F1 generation
b
b
Percentage
Ratio
Phenotype:
Genotype:
III. Incomplete Dominance
1. Give an example of incomplete dominance.
2. Refer to Lab Exercise 6, Cross 2. What would the offspring look like if two pink
snapdragons were crossed?
3. What percentage of the offspring in the above cross are pink?
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IV. Dihybrid Crosses
1. List the possible gametes which can be produced by an individual which is aaTT. Use
the foil method.
Parental genotype (diploid):
aaTT
Gametes (haploid):
2. After viewing the example in Lab Exercise 8, complete the following cross between
pea plants, AATT x AaTt, and give the phenotype ratio.
AT
AT
AT
AT
AT
AATT
At
aT
at
Ratio
Phenotype:
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3. Refer to Lab Exercise 9, Cross 1. Cross two corn plants: one homozygous dominant
AARR and one homozygous recessive aarr. When crossing two homozygous parents,
only one genotype of offspring is produced. Record the results below.
Percentage
Ratio
F1 Genotype:
F1 Phenotype:
4. Refer to Lab Exercise 9, Cross 2. Cross two heterozygous AaRr corn plants and
predict their offspring.
F1 Genotype (diploid):
X
Meiosis
Gametes (haploid):
F2 generation:
Percentage
Ratio
F2 Phenotype:
5. Refer to Lab Exercise 9, Cross 3. How does the actual percent of corn kernels
compare with the percent you predicted using Punnett squares above?
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Summary Questions
1. Who is Gregor Mendel?
2. In cats, white fur (b) is recessive to black fur (B). What are the possible genotypes of a
black-furred cat?
3. What is the difference between a monohybrid and dihybrid cross?
4. How is incomplete dominance different from complete dominance?
5. Cross a dog that is heterozygous with wire hair (Ww) with a dog that is homozygous
recessive with smooth hair (ww).
Percentage
Ratio
Phenotype:
Genotype:
6. A female rabbit, homozygous recessive for white fur, produces a litter of four bunnies.
All of the bunnies are black. Set up a Punnett square to determine the genotype of the
father.
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7. White wool (WW, Ww) and brown eyes (BB, Bb) are dominant traits in sheep, while
black wool (ww) and blue eyes (bb) are recessive. Determine the results of a cross
between a sheep with black wool and blue eyes and a sheep with white wool (Ww) and
brown eyes (BB).
Parental Genotype (diploid):
X
Gametes (haploid):
Phenotype:
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8. A species of clam shows incomplete dominance in the expression of its shell color. RR is
the genotype for a red shell, Rr is the genotype for an orange shell and rr is the
genotype for a yellow shell. Predict the outcome of a cross between an orange shelled
clam and a yellow shelled clam.
Phenotype
Genotype
Orange
Rr
Parent:
X
Phenotype
Genotype
Yellow
rr
meiosis
Gametes:
Percentage
Phenotype:
Ratio
Orange
Yellow
Genotype:
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BioLab3
Human Genetics Lab Report
Name, date, course and section required for password:
The lab report is unique each semester and checks have been put into place to ensure students are doing
their own work. Copying from other students or from outside resources will result in a zero on the
accompanying lab quiz.
I. Inheritance of Human Genetic Characteristics
1. Give an example of a human trait that shows incomplete dominance.
2. Refer to Lab Exercise 1. After completing the coin flip activity, draw what the
resulting child would look like. Sign, date and prepare an image your drawing and
include it with this lab report.
3. According to the information in Lab Exercise 1, in a random sample of 100 babies
born of heterozygous parents, what percentage do you predict would have freckles?
4. What is a pedigree and how is it useful?
5. In the pedigree in Lab Exercise 2, what percent of the F2 generation have free
earlobes?
6. How many pairs of autosomes do humans have?
7. Give two examples of an X-linked disorder.
8. When looking at a pedigree, how can you tell if an individual is a carrier of an
autosomal recessive trait?
9. In Lab Exercise 3, how many of the F2 generation have sickle-cell anemia?
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10. What is Hemophilia-A and how is it passed to one’s children?
11. Refer to Lab Exercise 4. What percent of the F2 females are carriers of color
blindness?
12. An individual has type A blood. What genotypes are possible?
13. In a case of disputed paternity, a child is type O, and mom is type B. Fill in the
information below and use Punnett squares to determine the possible blood types of
the father.
Mother’s genotype
Child’s genotype
Type
A
Type
O
Could he be the father?
Type
B
Could he be the father?
Type
AB
Could he be the father?
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Could he be the father?
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I.
Bioethics and the Human Genome Project
Select at least three articles provided and write a brief paragraph discussing how each
issue impacts you, your family, and society as a whole.
Article 1:
Article 2:
Article 3:
Summary Questions
1. Give examples of human traits that show these patterns of inheritance:
Complete dominance
Incomplete dominance
Polygenic inheritance
Codominance
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2. Queen Victoria of England was a carrier of the genetic disorder which causes
hemophilia A. The following diagram is a partial pedigree of her family. How many
of her daughters were carriers?
3. A mother has a small nose and a father has a medium size nose. Use the Punnett
square to determine the possible genotypes of their children.
4. Four siblings are tested for their blood type. Two are heterozygous for type A, and
the other two have type AB. What are the genotypes of the parents?
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5. A male carrier of albinism marries an albino female. Will any of their children show
albinism? Why?
6. Discuss a possible benefit of the human genome project.
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