Problem 1
• You send a blood sample from a dysmorphic infant to the
chromosome laboratory for analysis. The laboratory
report states that the child’s karyotype is
46,XY,del(18)(q12).
• a. What does this karyotype mean?
• b. The laboratory asks for blood samples from the
clinically normal parents for analysis. Why?
• c. The laboratory reports the mother’s karyotype as 46,
XX and the father’s karyotype as 46,
XY,t(7;18)(q35;q12). What does the latter karyotype
mean? Referring to the normal chromosome idiograms
sketch the translocation chromosome or chromosomes
in the father. Sketch these chromosomes in meiosis in
the father.
text problem 1 page 155
Answer Problem 1
•
•
You send a blood sample from a dysmorphic infant to the chromosome
laboratory for analysis. The laboratory report states that the child’s
karyotype is 46,XY,del(18)(q12).
a. What does this karyotype mean?
– The child has 46 chromosomes, male, with a deletion on the long arm of
chromosome 18 from q12 onward
•
b. The laboratory asks for blood samples from the clinically normal parents
for analysis. Why?
– To determine whether the abnormality is de novo or inherited from a balanced
carrier parent
•
c. The laboratory reports the mother’s karyotype as 46, XX and the father’s
karyotype as 46, XY,t(7;18)(q35;q12). What does the latter karyotype
mean?
– 46 chromosome, male, only one normal 7 and 18, reciprocal translocation
between 7 and 18 The regions after q35 on 7 and after q12 on18 have switch
•
Referring to the normal chromosome idiograms sketch the translocation
chromosome or chromosomes in the father. Sketch these chromosomes in
meiosis in the father.
text problem 1 page 155
Answer Problem 1
•
Referring to the normal chromosome idiograms sketch the translocation chromosome or
chromosomes in the father in his son. Sketch these chromosomes in meiosis in the father. What
kinds of gametes can he produce.
21
21
14
14
11.3
12
11.3
12
35
21
12
21
31
22
31
18
33
12
18
33
35
Translocation here
7
7
text problem 1 page 155
Answer Problem 1
Referring to the normal chromosome idiograms sketch the translocation chromosome or
chromosomes in the father in his son. Sketch these chromosomes in meiosis in the father.
31
21
12
14
21
33
31
21
12
14
21
12
33
11.3
35
11.3
•
22
Pairing at meiosis
text problem 1 page 155
Problem 2
Note this could be a picture of a dicentric
chromosome
• Considering the
chromosome spread
to the right.
• a. If this person was
phenotypically normal
and had 6 children
how many would you
expect to be
phenotypically normal
For this problem assume two separate chromosome in the picture
Answer Problem 2
• a.
If this person was phenotypically
normal and had 6 children how many would
you expect to be phenotypically normal
quadrivalent pair
formed during
meiosis
One completely normal individual
Two phenotypically normal individual
Four affected individuals
Problem 3
• Considering the follow
karotype.
• a. Is this individual
normal
• b. What is his karyotype
• c. If he is not what
syndrome does he have.
• d. What is one possible
mechanism to explain this
karotype
Answer Problem 3
•
•
Considering the follow karotype.
a. Is this individual normal
–
–
–
•
b. What is his karyotype
–
•
46 XY t(q21q:q21) 46 chromosomes, male with
translocation between the long are of chromosome 21
c. If he is not what syndrome does he have.
–
•
No, this individual is not
One chromosome is larger
It appears to be an isochromosome of 21
This individual is essentially trisomy for 21 so he
probably has Down Syndrome
d. What is one possible mechanism to explain this
karotype
–
Appears to be an isochromosome of 21. Chromosome
21 is acrocentric with the short arm (p) mainly
containing satellite DNA for ribosomal RNA.
Chromosomes 13,14,15, and 22 have a similar
structure. Loss of the short of 21 should cause little to
no deleterious affects. The duplication of the long arm
will result in trisomy 21. A similar event could occur in
chromosome 13, 14, 15, and 22 however only 21 will
produce a viable phenotype. Trisomy 13 is possible
but most cases die in a month
Problem 4
• Consider the karyotype to
the right.
• a. What syndrome does
the individual have?
• b. List the average
phenotypic features of a
13 year old individual
• c. Would this individual
be able to have normal
childern
Answer Problem 4
• Consider the
karyotype to the right.
• a. What syndrome
does the individual
have?
– This individual has
turner syndrome.
Probably due to
monosomy of the X
chromosome
Answer Problem 4
• b. List the average
phenotypic features of
a 13 year old
individual
• c. Would this
individual be able to
have normal childern
– No improper
development of the
ovaries
Problem 5
An individual presents with the following clinical
signs
Infantile feeding difficulties, childhood hyperphagia
and obesity, hypotonia, congnitive impairment,
sterility, and dysmorphism.
a. What syndrome does this individual have?
b. Which of the karyotypes below is most
consistent with the individuals syndrome.
c. What is one possible mechanism that may have
caused this syndrome.
Answer Problem 5
An individual presents with the following clinical
signs
Infantile feeding difficulties, childhood hyperphagia
and obesity, hypotonia, congnitive impairment,
sterility, and dysmorphism.
a. What syndrome does this individual have?
a. This individual probably has Prader Willi
syndrome
b. Which of the karyotypes below is most
consistent with the individuals syndrome.
a. The karyotype with no chromosomal
abnormalities
Klinefelter
Down Syndrome
Appears Normal
Turner Syndrome
Answer Problem 5
a. What is one possible mechanism that may have
caused this syndrome.
a. Because the karyotype is normal this
disorder may have been caused by
uniparental disomy. This is a type of
nondisjunction.