Chromosomes & Chromosomal Abnormalities

Question 1

Somatic nondisjunction during mitosis contributes to aneuploidy in cancer cells. This results from the failure of what cell cycle checkpoint?

Answer 1

Spindle assembly checkpoint in M phase

Question 2

How are the short and long arms of chromosomes identified?

Answer 2

Short arm - p

Long arm - q

Question 3

What is the most common cause of trisomies?

Answer 3

Nondisjunction

Question 4

What clinical features are associated with Down Syndrome?

Answer 4

Decreased intellectual ability, severe hypotonia in newborns, congenital abnormalities, increased risk of acute leukemia, abnormal immune response

Question 5

A cell has 69 chromosomes. Is this cell euploid or polyploid?

Answer 5

The cell is both euploid (multiple of 23 chromosomes) and polyploid (one complete set of extra chromosomes).

Haploid gametes and diploid cells are euploid, but not polyploid.

Question 6

Prader-Willi and Angelman syndromes may be associated with what chromosomal abnormality?

Answer 6

Microdeletions

Question 7

How do microdeletions differ from deletions?

Answer 7

In deletions, an entire chromsomal arm is deleted. In microdeletions, only a region or band is deleted.

Question 8

What are the structural chromosomal abnormalities?

Answer 8

Inversions, ring chromosomes, isochromosomes, translocations, deletion, microdeletions

Question 9

True/False. Phenotypes on ring chromosomes are associated with deleted genes.

Answer 9

True. Deletion of genes during formation of the ring chromosome results in phenotypic changes. If no genes are deleted then there will be no phenotypic changes.

Question 10

Differentiate between a submetacentric and acrocentric chromosome.

Answer 10

In a submetacentric chromosome, the centromere is located near the middle of the chromosome, but is not exactly in the center. This results in a short and a long arm.

In an acrocentric chromosome, the centromere is located at one end of the chromosome. This results in a short and a long arm. The short arm also contains satellites.

Question 11

What process takes place during meisos to increase genetic diversity of gametes by allowing for different combinations of traits?

Answer 11

Recombination via crossing over between homologous chromosomes

Question 12

True/False. Robertsonian translocations always result in mutant phenotypes.

Answer 12

False. Individuals with a Robertsonian Translocation are phenotypically normal. They are are increased risk of producing abnormal gametes, also increasing risk for chromosomal disorders such as Down Syndrome.

Question 13

What are the clinical features of Klinefelter syndrome?

Answer 13

In males - hypogonadism, gynecomastia, sparse body hair, reduced muscle mass

Infertility, normal IQ but predisposition for learning disabilities

Question 14

What are the sex chromosome aneuploidies?

Answer 14

Klinefelter Syndrome (XXY)

Turner Syndrome (45,X)

Trisomy X (XXX)

Jacob Syndrome (XYY)

Question 15

A newborn has rocker-bottom feet, a small head, and clenched fists. As the newborn ages, significant developmental disabilities and a congenital heart defect are noted. What disorder is causing the observed symptoms?

Answer 15

Edwards Syndrome - Trisomy 18

Question 16

Chromosome loci are named based on chromosome number, arm, region, and band. Identify the circle loci on the chromosome.

Answer 16

Xp11

Question 17

How can aneuploidy result from nondisjunction in meiosis?

Answer 17

Failure of homologous chromosomes to separate in meiosis I

OR
Failure of sister chromatids to separate during meiosis II

Question 18

What is an unbalanced chromosomal abnormality with loss of one arm and duplication of the other?

Answer 18

Isochromosome

Question 19

Flip to view a normal male karyotype.

Answer 19

Question 20

What are the two classes of chromosomal abnormalities?

Answer 20

Structural & numerical

Question 21

What is mosaicism?

Answer 21

Mosaicism is the concept that cells in the body may sometimes be genetically different than other cells, with different genotypes and phenotypes. The mature organism is a mosaic of mutated and non-mutated cells.

Question 22

What is a Robertsonian translocation?

Answer 22

Translocation involving two acrocentric chromosomes. The short arm of one chromosome is exchanged for the long arm of another to create a larger metacentric chromosome. Offspring are phenotypically normal. Any chromosome fragments that fail to integrate at degraded.

Question 23

What characteristics are associated with Trisomy X?

Answer 23

Sterility, irregular menses, mildly decreased IQ

Question 24

Why is the incidence of certain single-gene disorders associated with greater paternal age?

Answer 24

Primary spermatocytes undergo cell division beginning at puberty until death. The greater the number of cell divisions, the more likely point mutations and thus single-gene disorders are to occur.

Question 25

What causes isochromosomes?

Answer 25

Horizontal, rather than vertical, division

Question 26

The risk of chromosomal abnormalities increases with the age of which parent?

Answer 26

Mother - oocytes undergo meiotic arrests. Greater risk of nondisjunction or other chromosomal abnormalities is associated with longer oocyte arrest

Question 27

An individual is known to have germline mosaicism. What is their phenotype? What would be the phenotype of their offspring?

Answer 27

Germline mosaicism occurs if there is a mutation in embryonic development in all or some of the germline. The individual will display normal phenotype, but will pass the mutations to their offspring. Offspring may have normal or mutant phenotype.

Question 28

What disorders are associated with chromosomal deletions?

Answer 28

Wolf-Hirschhorn

Cri-du-chat

Question 29

What are the three autosomal trisomies?

Answer 29

Trisomy 21 - Down Syndrome

Trisomy 18 - Edwards Syndrome

Trisomy 13 - Patau Syndrome

Question 30

What is the difference between pericentric and paracentric inversion?

Answer 30

Paracentric inversions do not involve the centromere, while paricentric inversions do involve the centromere.

Question 31

The parent of teenage patient presents with concerns as the patient has not developed secondary sex characteristics. Upon observation, you also note the patient has short stature and webbed neck. What disorder is affecting the patient?

Answer 31

Turner Syndome

Question 32

The centromere is located in the middle of this type of chromosome, resulting in equal arms.

Answer 32

Metacentric chromosome

Question 33

What characteristics are associated with Jacob Syndrome?

Answer 33

Taller than average, reduced IQ, increased incident of behavioral disorders and learning disabilities

Question 34

What are the characteristics and clinical features of Patau Syndrome (Trisomy 13)?

Answer 34

Small head, sloping forehead, large nose, small eyes, cleft lip, significant developmental disabilities, malformation of CNS, heart defects, renal abnormalities

Question 35

How does mosaicism differ from chimerism?

Answer 35

In mosaicism, cells are from the same zygote and differ only by the result of a mutation. In chimerism, two zygotes fuse to form one embryo.

Question 36

What is a translocation?

Answer 36

A segment of one chromosome is transferred to another chromosome

Question 37

How does mixoploidy differ from aneuploidy?

Answer 37

In mixoploidy, only some cells have extra chromosomes in mosaic form. In aneuploidy, all cells have the addition or deletion of individual chromosomes.