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INET Lab
Genetics Worksheet Report Template
Student:
Email:
Date:
Please complete and submit this worksheet to earn 5 points.
1. There are 3 alleles controlling the ABO blood types. IA and IB are codominant genes so that the
combination IAIB produces the AB blood type. The third allele, (i) is recessive to the other two alleles.
Show your work for each cross.
Indicate which of these parents could produce the given child. Fill in all the blank spaces.
The first one is provided with answers as an example.
(HINT: Do not forget that a heterozygous versus a homozygous blood type may yield different results.)
a)
Parent
Child
A x AB
B
IA
IB
IA
IA IA
IA IB
IA
IA IA
IA IB
Produce Child of Type?
b)
No
Parent
Child
AxO
A
Allele?
IA
IB
IA
IA IA
IA IB
i
IA i
IB i
Produce Child of Type?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Produce Child of Type?
Allele?
Produce Child of Type?
Yes
c)
Parent
Child
AxB
O
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Produce Child of Type?
Allele?
Produce Child of Type?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Produce Child of Type?
d)
Parent
Child
A x AB
O
Allele?
Allele?
Produce Child of Type?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Produce Child of Type?
Allele?
Allele?
Produce Child of Type?
e)
Parent
Child
BxB
O
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Produce Child of Type?
Allele?
Allele?
Allele?
Allele?
Produce Child of Type?
f)
Parent
Child
AB x AB
A
Allele?
Allele?
Allele?
Allele?
Produce Child of Type?
Allele?
Produce Child of Type?
Autosomal Disorder
2. The allele for albinism (a) is recessive to the allele for normal pigmentation (A). A normally pigmented
woman whose father is an albino marries an albino man whose parents are normal. They have three
children, two normal and one albino. Give the genotypes for each person listed. Prove your answer.
1
2
3
5
4
6
7
9
8
#
Relationship
1
Paternal Grandfather
2
Paternal Grandmother
3
Maternal Grandfather
4
Maternal Grandmother
5
Father
6
Mother
7
Child 1
8
Child 2
9
Child 3
a) Show the cross of the paternal grandparents.
(HINT: What must their genotypes be to produce and albino child?)
Allele?
Allele?
Allele?
Allele?
b) What are the possible genotypes of the maternal grandmother?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Genotype(s)
c) Show the cross of the mother and father.
Allele?
Allele?
Allele?
Allele?
Test Cross
3. In horses, black coat color is influenced by the dominant allele (B), and chestnut coat color by the
recessive allele (b).
a) What color horse would you use to find out the genotype of a black trotter?
b) Give the genotype and phenotype. Show your work and discuss the reason you would know the
genotype of the black horse.
Possible Allele Pairings with Homozygous Dominant Trotter
Allele?
Allele?
Allele?
Allele?
F1 offspring probabilities:
Possible Allele Pairings with Heterozygous Trotter
Allele?
Allele?
Allele?
Allele?
F1 offspring probabilities:
Reasoning:
X-Link Disorder
4. In Drosophila, the fruit fly, white eyes are determined by a recessive X-linked gene, and the wild-type
or normal brick-red eyes are due to its dominant allele. Use symbols of the following types: X rY = a whiteeyed male; XRXR = a homozygous normal red female.
a) What offspring can be expected from a cross of a white-eyed male and a homozygous normal female?
b) Show the genotypes and list the phenotypes of the F1 offspring.
F1 Cross
Allele?
Allele?
Allele?
Allele?
F1 offspring probabilities:
Male
Female
Red-Eyed
White-Eyed
c) Now, cross the F1 offspring. Show the genotypes and list the phenotypes of the F 2 offspring.
F2 Cross
Allele?
Allele?
Allele?
Allele?
F2 offspring probabilities:
Male
Red-Eyed
White-Eyed
Female
INET Lab
Genetics Worksheet Report Template
Student:
Email:
Date:
Please complete and submit this worksheet to earn 5 points.
1. There are 3 alleles controlling the ABO blood types. IA and IB are codominant genes so that the
combination IAIB produces the AB blood type. The third allele, (i) is recessive to the other two alleles.
Show your work for each cross.
Indicate which of these parents could produce the given child. Fill in all the blank spaces.
The first one is provided with answers as an example.
(HINT: Do not forget that a heterozygous versus a homozygous blood type may yield different results.)
a)
Parent
Child
A x AB
B
IA
IB
IA
IA IA
IA IB
IA
IA IA
IA IB
Produce Child of Type?
b)
No
Parent
Child
AxO
A
Allele?
IA
IB
IA
IA IA
IA IB
i
IA i
IB i
Produce Child of Type?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Produce Child of Type?
Allele?
Produce Child of Type?
Yes
c)
Parent
Child
AxB
O
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Produce Child of Type?
Allele?
Produce Child of Type?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Produce Child of Type?
d)
Parent
Child
A x AB
O
Allele?
Allele?
Produce Child of Type?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Produce Child of Type?
Allele?
Allele?
Produce Child of Type?
e)
Parent
Child
BxB
O
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Produce Child of Type?
Allele?
Allele?
Allele?
Allele?
Produce Child of Type?
f)
Parent
Child
AB x AB
A
Allele?
Allele?
Allele?
Allele?
Produce Child of Type?
Allele?
Produce Child of Type?
Autosomal Disorder
2. The allele for albinism (a) is recessive to the allele for normal pigmentation (A). A normally pigmented
woman whose father is an albino marries an albino man whose parents are normal. They have three
children, two normal and one albino. Give the genotypes for each person listed. Prove your answer.
1
2
3
5
4
6
7
9
8
#
Relationship
1
Paternal Grandfather
2
Paternal Grandmother
3
Maternal Grandfather
4
Maternal Grandmother
5
Father
6
Mother
7
Child 1
8
Child 2
9
Child 3
a) Show the cross of the paternal grandparents.
(HINT: What must their genotypes be to produce and albino child?)
Allele?
Allele?
Allele?
Allele?
b) What are the possible genotypes of the maternal grandmother?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Allele?
Genotype(s)
c) Show the cross of the mother and father.
Allele?
Allele?
Allele?
Allele?
Test Cross
3. In horses, black coat color is influenced by the dominant allele (B), and chestnut coat color by the
recessive allele (b).
a) What color horse would you use to find out the genotype of a black trotter?
b) Give the genotype and phenotype. Show your work and discuss the reason you would know the
genotype of the black horse.
Possible Allele Pairings with Homozygous Dominant Trotter
Allele?
Allele?
Allele?
Allele?
F1 offspring probabilities:
Possible Allele Pairings with Heterozygous Trotter
Allele?
Allele?
Allele?
Allele?
F1 offspring probabilities:
Reasoning:
X-Link Disorder
4. In Drosophila, the fruit fly, white eyes are determined by a recessive X-linked gene, and the wild-type
or normal brick-red eyes are due to its dominant allele. Use symbols of the following types: X rY = a whiteeyed male; XRXR = a homozygous normal red female.
a) What offspring can be expected from a cross of a white-eyed male and a homozygous normal female?
b) Show the genotypes and list the phenotypes of the F1 offspring.
F1 Cross
Allele?
Allele?
Allele?
Allele?
F1 offspring probabilities:
Male
Female
Red-Eyed
White-Eyed
c) Now, cross the F1 offspring. Show the genotypes and list the phenotypes of the F 2 offspring.
F2 Cross
Allele?
Allele?
Allele?
Allele?
F2 offspring probabilities:
Male
Red-Eyed
White-Eyed
Female
Curse of the Garcias
Discover Dec. 2000
Why are so many women in this family unable to conceive?
An early medical description of a condition similar to androgen insensitivity appeared in
a German journal in 1817. The role of sex chromosomes in the syndrome was not
discovered until 1937. The incidence of androgen insensitivity is roughly one in 50,000.
Two facts about Imelda Garcia struck me when Ellen, our genetics counselor, introduced her.
First, she seemed unusually nervous. Her hands were balled tightly into fists and her lips were
clenched. Second, she was strikingly attractive, with a tall, well-proportioned body, pretty face,
and long, dark hair. “you seem nervous,” I began, thinking that an obvious statement might put
her more at ease. She was silent for a moment. I tried again. “What’s the matter?”
“I’m supposed to be at school now,” she answered. “And if my parents knew I was here, they
would be very angry.”
“Why would they be angry?” Ellen asked.
“They say, There’s nothing wrong with you. They say, God made me this way and nothing
cam be done to change that. But I don’t believe that. What kind of a God would do that?”
“In the town where I was born, a lot of women have the same problem as I do. They call it
“The Curse of the Garcias’ because so many in my mother’s family have it. Although all of us
look and act like everyone else, we are very, very different.”
“In what way?” Ellen asked.
“None of us can bear children. We never even get out period.”
As Imelda began telling her story, Ellen recorded the family history. Imelda was the
seventh of eight children, and she had lived on a small farm in Mexico until her parents moved
the family to New York City five years ago. Two of her older sisters, she said, were also
affected. The problem stretched back at least four generations: Three of her mother’s four
sisters had the condition. Over four generations, I counted a total of 16 childless women. That
pattern was already suggesting that the syndrome was linked somehow to a problem on the X
chromosome.
“My mother says she can tell from the time a girl is 4 or 5 whether she is cursed or
not,” added Imelda, “but it isn’t until we are teenagers that things begin to change.”
“How does she know?” I interrupted.
“She says we are prettier than the other girls. But I know that if I could trade being
pretty for being normal, I’d do it in a second. In Mexico, girls are treated like royalty when
they get their period. But those of us who aren’t able to have children are treated like slaves.
We are forced to serve the others, to care for them, cook and clean for them. We can’t marry.
And then, when we become too old to work, we’re banished from the houses of our relatives.”
“Is that why your family came to New Your?” I asked.
“Yes. My parents wanted to do anything they could to make sure that we wouldn’t end up
that way. So they gave up everything to move here. Still, they don’t want us to talk to doctors.
But I’ve learned in biology class about hormones. I’ve been thinking this may be an endocrine
imbalance.”
“Before we can talk about helping you, we have to figure out exactly what’s wrong.” I
responded. “It’s certainly possible we’ll find out you have a simple problem that can be treated
with hormones or some other medication. But it it’s also possible we’ll find a condition we
can’t fix. Are you willing to go ahead, knowing that we may wind up taking away the hope you
have now?”
Imelda considered my question for a few moments before answering. “You’re right that I
have some hope now. But I want to find out, even if it means I have to accept the fact that
nothing can be done to help me.”
“All right,” I replied. “Let me tell you what we’re going to do. First, I’m going to examine
you. Then I’m going to take blood for some tests. Those tests may tell us the diagnosis. When
we get the test results, we’ll talk about what can or cannot be done.
Ellen and I left the room. I asked her what she thought the problem might be. Without
hesitation, she replied: “Androgen insensitivity syndrome.” I agreed.
In Human Development, being female is, to use computer terminology, the default. Unless it
receives other signals, the embryonic tissue that gives rise to the external genitalia will from
itself into normal female structures during the first trimester. Making a male is more complex.
A gene called SRY on the Y chromosome must prompt the undifferentiated embryonic gonad
to become a testis during the seventh week after conception. That testis must then produce
testosterone, one of a class of male hormones called androgens. Next. Testosterone molecules
must attach themselves to the surface of the individual cells that form the embryonic sex ducts,
the structures that ultimately give rise to the external genitalia. If these cells can recognize
testosterone, male development proceeds by prompting the female-forming structures, known
as the Mullerian ducts, to degenerate and the male-forming structures, called Wolffian ducts, to
differentiate into the organs and ducts needed for male development. Any irregularity in this
pathway will lead to either incomplete male development or the production of an externally
“normal looking” female.
In individuals affected with androgen insensitivity syndrome, also known as “testicular
feminization,” the first three steps occur normally – individuals inherit an X and a Y
chromosome, the SRY gene on the Y chromosome signals the undifferentiated gonads to form
into testes, and the testes produce normal amounts of testosterone. But then, because of an
error in a gene carried on the X chromosome, the cells that are supposed to bind testosterone to
their surface and initiate male development can’t recognize it. So, in spite, of carrying a Y
chromosome and making lots of testosterone, these individuals develop into women who have
testes in their abdomen instead of ovaries, Because the male-making effects of testosterone are
tharted, the body converts the hormone to estrogen, so these women tend to develop full
figures. Overall, they are perfectly healthy, but the testes can, in rare cases, turn cancerous, so
they’re usually removed when the patient completes development. At that point, the patient
must begin estrogen replacement to avoid entering menopause.
Imelda’s exam showed she was not normal in two ways. There was no axillary or pubic
hair, and her vagina was very short, ending in a blind pouch. Given her exam and the
abundance of affected women in her family history, I was nearly certain that the Garcias’
problem resulted from inherited S-linked androgen insensitivity syndrome. But I would need a
blood test to confirm the diagnosis. The test indeed showed that Imelda had one X and one Y
chromosome in her cells. And her hormone testing showed an extraordinarily high level of
testosterone. Her endocrine system was screaming for her body to make a man, but her cells
were deaf to those instructions.
Before Imelda returned to discuss the tests, Ellen and I had decided to let Imelda start with
her own questions. We agreed that we wouldn’t tell Imelda about the results of the genetic test
unless she brought it up. Telling a woman she has the chromosome complement of a man can
have long-term and far-reaching psychological consequences.
When Imelda arrived, I started by saying, “The tests showed that you have an alteration in
one of your genes. This gene is responsible for causing your internal structures to mature.”
“Does that mean something is wrong with the gene that causes estrogen to be made?”
Imelda asked.
“Not exactly,” I replied. “It’s the gene that causes the cells of the body to be able to
recognize the presence of the sex hormones. Because of the way the gene is altered, your
internal structures are unable to recognize hormones. As a result, they did not develop as they
should have, and when you’re a few years older, you’ll need an operation to remove your
gonads.”
“Does this mean my womb didn’t develop?” Imelda asked.
I nodded
“You mean I can’t have children?”
Her eyes filled with tears.
“Imelda, I wish we’d found something that would bet better with medication. I ‘m sorry.”
“This doesn’t make you any less of a person,” Ellen said. “You’re not in Mexico now,
you’re in New York. And in New York, women who can’t have children aren’t considered
useless, hopeless people. You’re young, you’re smart, and you have your whole life ahead.
You can be anything you want to be”
“Except a mother,” Imelda added.
“It is true that because of this problem you won’t be able to bear children of your own ,” I
said. “But you can always adopt children. And being a mother to an adopted child is just as
satisfying as being a mother to a child you’ve borne yourself.”
There was silence in the room for a few seconds. “When I cam e here last week,” Imelda
finally said, “you asked if I wanted to go ahead with this, even though there was a chance I”d
find out that nothing could be done. Even though it worked out this way, I think I made the
right decision.”
I was glad she felt that way, but I found this a frustrating message to deliver. In recent
years, thanks to the genetic revolution, physicians can discover detailed answers to complex
diagnostic questions that used to remain mysteries. But the answers don’t necessarily make
anything better. In one way or another, we all have to live with who our genes have dictated we
are.
The case described in Vital Signs is based on a true story. Some details have been changed to
protect the patient’s privacy.
Robert Marion is a professor of genetics at Albert Einstein College of Medicine and director of
genetics at Montefiore Medical Center in New York City. Although androgen insensitivity is
relatively rare, Marion says he sees about one case every five years. Marion’s recent books
include Learning to Play God and Intern’s Blues.
The Curse of the Garcias – Androgen Insensitivity Question Sheet
1. What aspect of Imelda’s family history was unusual?
2. Which of Imelda’s chromosomes carries the mutant gene?
3. Did Imelda receive her mutant gene from her mother or her father?
4. Where is the SRY gene located and what does it do? (On which chromosome number )
5. Does Imelda have a mutated SRY gene?
6. What happens if a developing fetus doesn’t receive an SRY gene?
7. Does Imelda produce the male sex hormone, testosterone?
8. Why didn’t the testosterone trigger the development of male characteristics when Imelda
was a fetus?
9. What happens to the testosterone that Imelda produces?
10. If you were the doctor in this article, would you have given Imelda all the details?
11. If you were Imelda, would you have wanted all the details?
12. What do you think; Is Imelda a man or a woman?
13. If a technique were available to correct this mutation, would you support its use if …… ?
 The developing embryo could be tested for the mutant chromosome and it could be
swapped for a normal chromosome.
 Eggs could be screened for the mutant gene and discarded. Only eggs containing the
normal chromosome allowed to be fertilized.
On the back of the paper, draw a possible lineage/pedigree chart for Imelda’s family
with the information provided in the article.

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