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.

text problem 1 page 155

7

18

21

14

12

21

31

3335

11.3

12

22

Translocation here

7

18

21

14

12

21

31

3312

11.3

35

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.

text problem 1 page 155

21

14

12

21

31

33

35

11

.3 12 21

14

12

2131

33

22

11

.3

Pairing at meiosis

Problem 2

• 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

Note this could be a picture of a dicentric chromosome

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 individualTwo phenotypically normal individualFour 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

– No, this individual is not– One chromosome is larger– It appears to be an isochromosome of 21

• 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.

– 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 5An individual presents with the following clinical

signsInfantile 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 5An individual presents with the following clinical

signsInfantile 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

syndromeb. Which of the karyotypes below is most

consistent with the individuals syndrome.a. The karyotype with no chromosomal

abnormalities

Down SyndromeKlinefelter Appears Normal Turner Syndrome

Answer Problem 5a. 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.