Aneuploidies

Question 1

What is euploidy?

Answer 1

The presence of a whole multiple of haploid chromosome sets.

Question 2

What is diploidy?

Answer 2

Two copies of each chromosome.

Question 3

What is polyploidy?

Answer 3

The presence of extra sets of chromosomes.

Question 4

What is the fate of individuals born with triploidy?

Answer 4

They can be liveborn but they do not survive long.

Question 5

What error results in tetraploidy, what are the possible chromosome abbreviations, and what is the individual’s fate?

Answer 5

Tetraploidy (92, XXXX or XXYY) results from failure of early division of zygote, and the fetus does not survive to birth.

Question 6

What is aneuploidy?

Answer 6

Deviation from whole multiple of haploid chromosome set.

Question 7

What is monosomy? and what is the individual’s fate?

Answer 7

The loss of one copy of a particular chromosome; lethal if it occurs with an autosome.

Question 8

What is trisomy and what is the individual’s fate?

Answer 8

Having an extra copy of a particular chromosome; all are lethal except 13, 18, and 21.

Question 9

How do monosomy and trisomy arise?

Answer 9

They arise from nondisjunction during meiosis (I mostly but II also possible). But can also occur during mitosis, shortly after the zygote has formed, producing a mosaic.

Question 10

What trisomy is the least severe?

Answer 10

Trisomy 21

Question 11

Why are trisomy 13, 18, and 21 the only viable trisomies?

Answer 11

Because they have the fewest genes on them.

Question 12

At what meiotic stage and in what parent is Trisomy 21 most likely to occur?

Answer 12

90% meiosis I in mom, 10% meiosis II in dad

Question 13

Which of these is not a symptom of Down Syndrome?
Hypotonia
Flat facial profile
Brachycephaly
Upslanting palpebral fissures
Receeding jaw
Loose skin on neck
Furrowed or protruding tounge
Short stature
Mental retardation

Answer 13

Receeding jaw is seen in Trisomy 18

Question 14

What are the complications associated with Trisomy 21?

Answer 14

Congenital heart disease (poor prognosis), duodenal atresia, tracheoesophogeal atresia, leukemia (15x risk), and early onset Alzheimer.

Question 15

What are the chromosomal structural anomalies that lead to Down Syndrome.

Answer 15

Trisomy 21 (95%), Robertsonian translocation (4%), 21q21q translocation (few), Mosaic- mix of normal and trisomy (2%), and Partial trisomy- extra piece/part of chromosome 21 (rare, but maybe helpful in understanding responsible genes!)

Question 16

How is that a Robertsonian translocation that involves Chromasome 21 result in a viable individual if both p arms (and thus their genes) are lost?

Answer 16

Chromosome 21 is acrocentric, so there aren’t many genes on the p arm to begin with. Also, info on 21p is repeated on other chromosomes, so loss of this information can be okay.

Question 17

True or False: The recurrence risk for ANY trisomy after one affected child is ~1% for another child being affected. In addition, a history of trisomy elsewhere in the family increases the risk further.

Answer 17

False, family history of the same trisomy does not increase the recurrence risk for a second child having the trisomy (exception: Robertsonian or other translocations).

Question 18

What percent of Trisomy 18 (Edward Syndrome) conseptuses spontaneously abort.

Answer 18

95%

Question 19

Which of the following are not symptoms of Edward Syndrome?
Mental retardation
Failure to thrive, poor feeding
Heart malformation
Hypertonia
Fist clench with 2nd and 5th digit over 3rd and 4th
Loose skin on neck
Prominent occiput, receeding jaw
Usually die by year 1

Answer 19

Loose skin on neck is associated with Down syndrome

Question 20

What error in meiosis is likely the cause for Edward Syndrome?

Answer 20

Maternal nondisjunction most common (translocation of most/all of Chrom. 18 or mosaic trisomy less common)

Question 21

Which of the following are not symptoms of Patau Syndrome (Trisomy 13)?
Severe mental retardation
Flat facial profile
Failure to thrive, poor feeding
Heart malfomation
Hypertonia
Fist clench with 2nd and 5th digit over 3rd and 4th
Long protruding forehead, cleft lip/palate
May show polydactyly
Half die within first month

Answer 21

Flat facial profile

Question 22

What part of of meiosis does Trisomy 13 result from?

Answer 22

Maternal nondisjunction during meiosis I

Question 23

What is the most common Chromosome count for Klinefelter Syndrome

Answer 23

47,XXY (Additional Xs increase severity)

Question 24

True or False: Klinefelter Syndrome is RARE in spontaneous abortions.

Answer 24

True

Question 25

Which of the following are not symptoms of Klinefelter Syndrome?
Elevated renal and cardiovascular abnormalities
Tall, thin
Hypogonadism
Infertile
Learning disabilities and poor psychosocial adjustment

Answer 25

Elevated renal and cardiovascular abnormalities is associated with Turner Syndrome

Question 26

What is the most likely meiotic cause of Klinefelter Syndrome?

Answer 26

Half result from errors in paternal meiosis I, most others from errors in maternal meiosis I (15% are mosaics who lost extra X after first division :))

Question 27

What meiotic error MUST cause 47, XYY Syndrome?

Answer 27

Nondisjunction in Male Meiosis II

Question 28

What are the two main symptoms of 47,XYY Syndrome?

Answer 28

Generally tall, increased risk of educational or behavioral problems.

Question 29

True or False: Having 47,XYY Syndrome means a father is more likely to pass it to his sons.

Answer 29

False: there is no apparent increased risk that they will father chromosomally abnormal children because the extra Y is often lost during chromosomal segregation.

Question 30

Which of the following are not associated with increased risk with increasing maternal age?
Down Syndrome
Edward Syndrome
Patau Syndrome
Klinefelter Syndrome
47,XYY Syndrome
Trisomy X
Turner Syndrome

Answer 30

47,XYY and Turner Syndrome risks do not increase with increasing maternal age

Question 31

Which of the following are not symptoms of Trisomy X?
70% have learning disability (Dec. IQ)
Slightly shorter than average
Increased severity of Sx with more X chromosomes

Answer 31

Trisomy X individuals will be slightly taller than average

Question 32

True or false: Having Trisomy X will increase the risk of having children with Trisomy X

Answer 32

True (Unlike 47,XYY Syndrome)

Question 33

What part of meiosis does Trisomy X originate from?

Answer 33

Most errors occur in maternal meiosis I (increased risk with maternal age), some in II

Question 34

What is the only viable human monosomy?

Answer 34

Turner Syndrome (45,X)

Question 35

Which of the following are not symptoms of Turner Syndrome?
Short stature
gonadal dysgenesis
webbed neck, low posterior hairline
elevated renal and cardiovascular anomalies
edema of foot dorsum at birth
Rocker-bottom foot at birth
Normal intelligence, but delayed development

Answer 35

Rocker-bottom foot is associated with Edward Syndrome

Question 36

Besides 45,X, what other chromosomal pattern can result in Turner Syndrome?

Answer 36

46,X,i(Xq) = isochromosome
45,X/46,XX mosaic
45,X/46,X,i(Xq) mosaic

Question 37

What meiotic errors result in Turner Syndrome?

Answer 37

70% of the time, Dad failed to give an X chrom. Sometimes a small ring X is detected (46,X,r(X))–will show mental retardation as a Sx! (due to lack of Xic on r(X)).