HRR: chromosomal abnormalities II

Question 1

Do sex chromosome abnormalities tend to be more or less severe?

Answer 1

Less; there is less genetic information of sex chromosomes.

Question 2

What is Turner’s syndrome?

Answer 2

Monosomy X (female missing X).

Question 3

What are features of monosomy X?

Answer 3

Webbed neck, aortic defects, horseshoe kidney, ovarian issues, lymphedema of hands and feet, and normal intelligence.

Question 4

A baby is born with horseshoe kidney. What should we test for?

Answer 4

Turner’s syndrome.

Question 5

What does a mosaic type of Turner’s syndrome convey risk for?

Answer 5

Gonadoblastoma.

Question 6

What percent of Turner’s syndrome babies result in live birth?

Answer 6

1%. Normally it results in spontaneous abortion.

Question 7

What is Klinefelter’s syndrome?

Answer 7

XXY (male with extra X).

Question 8

What are features of Klinefelter’s syndrome?

Answer 8

Infertility, hypogonadism, gynecomastia, speech delay and motor issues, sparse hair, female fat distribution.

Question 9

What causes Klinefelter syndrome?

Answer 9

Nondisjunction in meiosis I either from maternal or paternal meiosis.

Question 10

What are balanced chromosome rearrangements?

Answer 10

All genetic material remains present, and phenotype is typically normal.

Question 11

What is the issue with balanced chromosome rearrangements?

Answer 11

Abnormal offspring.

Question 12

What are unbalanced chromosome rearrangements?

Answer 12

Results in a gain or loss of genetic material, often causing abnormal phenotype.

Question 13

What are reciprocal translocations?

Answer 13

Two chromosomes give each other sections of their material.

Question 14

Does reciprocal translocation usually lead to balanced or unbalanced rearrangement?

Answer 14

Balanced rearrangement.

Question 15

Describe meiosis I in balanced reciprocal translocations.

Answer 15

Tetrads that are formed arrange in a quadrivalent (cross-like) patterns as opposed to bivalent (next to each other). This helps ensure correct alignment of homologous sequences during prophase I.

Question 16

What are the 3 options following segregation of quadrivalent chromosomes during meiosis I?

Answer 16

Alternate segregation (balanced), adjacent I segregation (unbalanced), or adjacent II segregation (unbalanced). Unbalanced will be abnormal.

Question 17

What are Robertsonian translocations?

Answer 17

Two acrocentric chromosomes that fuse near the centromere and result in loss of p arms (short arms).

Question 18

What are the acrocentric chromosomes?

Answer 18

13, 14, 15, 21, 22.

Question 19

What kind of karyotype is seen in Robertsonian translocations?

Answer 19

45 chromosomes. Tends to be balanced and normal phenotype.

Question 20

Carriers of Robertsonian translocations involving 21 are at risk of…

Answer 20

Having a child with translocation down syndrome.

Question 21

What is an inversion?

Answer 21

A single chromosome undergoes two breaks, and the segment inverts. An ABCD sequence would become ACBD.

Question 22

What is a paracentric inversion?

Answer 22

Both breaks occur in one arm.

Question 23

What is a pericentric inversion?

Answer 23

Breaks occur in each arm, including the centromere. The centromere is included in the inversion.

Question 24

What is the phenotypical outcome of inversions?

Answer 24

Phenotype is normal, but there is a risk for abnormal gametes.

Question 25

What is the outcome of gamete variations in paracentric inversions?

Answer 25

Half will come out fine, but half will be inviable due to missing information.

Question 26

What is the outcome of gamete variations in pericentric inversions?

Answer 26

Half will be balanced, and half will be unbalanced. This can result in miscarriages, duplications, deletions.

Question 27

Describe deletions.

Answer 27

Loss of chromosome material results in chromosome imbalance. Severity depends on size as well as what region of the segment is deleted.

Question 28

What is cri du chat syndrome?

Answer 28

A terminal deletion of 5p.

Question 29

How can we detect cri du chat?

Answer 29

Karyotype or microarray.

Question 30

What are features of cri du chat?

Answer 30

Small head, characteristic cry, wide space between eyes, developmental delays, round moon face.

Question 31

What is Wolf-Hirschhorn syndrome?

Answer 31

Terminal deletion of 4p.

Question 32

What are features of Wolf-Hirschhorn syndrome?

Answer 32

“Greek warrior helmet appearance” aka broad forehead and no sunken in nasal bridge, microcephaly, short philtrum, hypotonia, seizures, cleft lip and palate.

Question 33

What is DiGeorge syndrome?

Answer 33

An interstitial microdeletion that can be detected on microarray.

Question 34

What are features of DiGeorge syndrome?

Answer 34

Cardiac defects, abnormal facial features, thymic hypoplasia, cleft palate, hypoparathyroidism and hypocalcemia.

Question 35

What is Williams syndrome?

Answer 35

Interstitial microdeletion on the 7th chromosome.

Question 36

What are features of Williams syndrome?

Answer 36

Very outgoing, elfin-like face, cardiac defects, infantile hypercalcemia, stellate iris, intellectual disability.