Download Sex Chromosomes - NC Biology Resources

Unit 6D & E
Sex Linked Traits &
Pedigrees
**This needs to be separated into two
sections and the sex link traits need to be
expanded to include sex linked disorders**
A. Review of Concepts
A. Intro to the Basics of Genetics
G:\14-1 Human Heredity\0 Intro & Close\Intro Tour of the Basics.htm
B. Review Dominant & Recessive
C. Punnett Squares
Bikini Bottom Genetics W.S. –
Punnett Squares –
http://sciencespot.net/media/gen_
spbobgenetics.pdf
D. pg. 341 Vocab Preview
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Section:
Human Chromosomes
What do you think that sex chromosomes are?
Sex Chromosomes are the two chromosomes that determine an
organism’s sex. They also code for a few other characteristics.
– The two sex chromosomes can be either an X or a Y.
– The X codes for female, while the Y codes for male.
Autosomes are all of the other chromosomes – all the chromosomes a
that are not the sex chromosomes.
In humans there 23 homologous pairs of chromosomes, totaling 46
chromosomes:
2 sex chromosomes
44 autosomes
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Checkpoint Questions
1. What is a karyotype?
2. What are the sex chromosomes?
3. Which sex chromosomes do female have?
4. Which sex chromosomes do males have?
5. How many chromosomes are in the human genome?
6. How many autosomes are in the human genome?
7. How many sex chromosomes are in the human genome?
8. How many pairs of chromosomes are in the human genome?
9. What are the chances of having a boy?
10.Draw a Punnett Square representing the gametes of a cross
between a male and a female.
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Interest Grabber
Section 14-1
A Family Tree
To understand how traits are passed on from generation to generation, a
pedigree, or a diagram that shows the relationships within a family, is used.
In a pedigree, a circle represents a female, and a square represents a
male. A filled-in circle or square shows that the individual has the trait being
studied. The horizontal line that connects a circle and a square represents
a marriage. The vertical line(s) and brackets below that line show the
child(ren) of that couple.
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Interest Grabber continued
Section 14-1
1. This pedigree shows the inheritance of attached ear lobes. Which
parent has attached ear lobes?
2. How many children do the parents have? Which child has attached ear
lobes?
3. Which child is married? Does this child’s spouse have attached ear
lobes? Do any of this child’s children have attached ear lobes?
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Section:
Figure 14-3 A Pedigree
Section 14-1
A circle represents
a female.
A horizontal line connecting
a male and female
represents a marriage.
A half-shaded circle
or square indicates
that a person is a
carrier of the trait.
A completely
shaded circle or
square indicates
that a person
expresses the
trait.
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Section:
A square represents
a male.
A vertical line and a
bracket connect the
parents to their children.
A circle or square
that is not shaded
indicates that a
person neither
expresses the trait
nor is a carrier of
the trait.
Reading the Pedigree
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Section:
The pedigree below is for a genetic disease or abnormality. We do
not yet know if it is dominant or recessive. We will determine if it is
possible that the trait is autosomal dominant. If the trait were
dominant, we would use the following designations:
A = the trait (a genetic disease or abnormality, dominant)
a = normal (recessive)
If the trait were recessive, we would use the following
designations:
A = normal (dominant)
a = the trait (a genetic disease or abnormality, recessive)
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The pedigree shows that three of the individuals have the
recessive (normal) phenotype and one individual has the
dominant (abnormal) phenotype.
1. Write the genotype of the affected (abnormal) individual
next to her symbol in the pedigree below. If you only know
one of the genes (letters), use a "?" for the unknown
letter.
2. Is it possible that the pedigree above is for an autosomal
dominant trait?
3. Write the genotypes next to the symbol for each person in
the pedigree below assuming that it is for a dominant
Is it possible that this pedigree is for an
autosomal dominant trait?
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2. We will determine if the pedigree below can be for a trait that is
autosomal dominant. Use "A" and "a" as you did for the pedigrees
above.
a) Write the genotype of each individual next to the symbol.
b) Is it possible that this pedigree is for an autosomal dominant
trait?
c) In conclusion, can two individuals that have an autosomal
dominant trait have unaffected children?
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a) Assuming that the trait is recessive, write the genotype of each
individual next to the symbol.
b) Is it possible that the pedigree above is for an autosomal recessive
trait?
c) Assuming that the pedigree below is for a recessive trait, write the
genotype next to the symbol for each person.
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d) Is it possible that this pedigree is for an autosomal recessive trait?
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4. We will determine if the pedigree below can be for a trait that is
autosomal recessive. Use "A" and "a" as you did for the previous
example.
a) Write the genotype of each individual next to the symbol.
b) Is it possible that this pedigree is for an autosomal recessive trait?
c) If a trait is autosomal recessive, what can you conclude about the
children of two parents that are not affected? Put your answer to this
question in the summary table (item #4) in the answer sheet.
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Section:
We will determine if the pedigree below can be for a trait that is
autosomal recessive.
a) Write the genotype of each individual next to the symbol.
b) Is it possible that this pedigree is for an autosomal recessive trait?
c) In this pedigree, two generations have been skipped. What can you
conclude about recessive traits skipping generations? Put your answer to
this question in the summary table (item #5) in the answer sheet.
X-Linked Recessive
The conclusions that you made for autosomal recessive
traits apply to X-linked traits. In this exercise, we will
work on some additional conclusions because males
have only one X chromosome and females have two.
6. We will determine if the pedigrees below can be for a
trait that is X-linked recessive. Use the following
designations:
XA = normal
Xa = the trait (a genetic disease or abnormality)
Y = Y chromosome (males only)
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Section:
a) Write the genotype of each individual next to the symbol.
b) Is it possible that the pedigree above is for an X-linked recessive
trait?
c) Write the genotype next to the symbol for each person in the pedigree
below.
d) Is it possible that this pedigree is for an X-linked recessive trait?
e) Write the genotype next to the symbol for each person in the pedigree
below.
f) Is it possible that this pedigree is for an X-linked recessive trait?
g) Write the genotype next to the symbol for each person in the pedigree
below.
h) Is it possible that this pedigree is for an X-linked recessive trait?
a) Write the genotype of each individual next to the symbol.
b) Is it possible that this pedigree is for an X-linked recessive trait?
c) Which parent did the son get the Xa gene from?
d) What can you conclude about father-to-son transmission of X-linked
traits?
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a) Write the genotype of each individual next to the symbol.
b) Is it possible that this pedigree is for an X-linked recessive trait?
c) What can you conclude about the children if both parents are affected
with an X-linked recessive trait?
d) How does this conclusion compare with the one you made earlier if
about both parents being affected by an autosomal recessive trait?
e) Do the conclusions that you made for autosomal recessive traits apply
to X-linked recessive traits?
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9a. If a genetic disease is X-linked recessive, what is the
phenotype of a female that has only one disease allele (Xa)?
b. What is the phenotype of a male with one disease allele?
c. What can you conclude about the number of males that would
have the disease compared to the number of females?
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Pedigree for the Albino Trait
Pedigree for a Sex Linked Trait
Concept Questions
1.
2.
3.
4.
5.
6.
7.
What is a pedigree?
What is recessive?
What is dominant?
What is hetrozygous?
What is homozygous?
What is meant by X-linked?
What could be the genotype of a person with an autosomal recessive
disorder?
8. What could be the genotype of someone who didn’t display any characteristics
of an autosomal recessive disorder?
9. What could be the genotype of the son of a man who had and X-linked
disorder?
10. A man has an X-linked disorder. His wife does not. Will is daughter have it?
11. A woman has an X-linked disorder. Her husband does not have it. Will their
daughter have it?
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