Chromosome Structure

Question 1

What is a chromosome composed of?

Answer 1

one very long, double-stranded DNA molecule.

Question 2

What is a metacentric chromosome?

Answer 2

centromere is close to the middle of DNA molecule

Question 3

What are the acrocentric chromosomes in humans?

Answer 3

13,14,15,21,22
p arm has a special structure that contains all the ribosomal RNA genes. It is ok to be missing one or more acrocentric short arms and still be perfectly normal.

Question 4

What is a submetacentric chromosome?

Answer 4

centrosome is off-center.

Question 5

What is the p-arm? q-arm?

Answer 5

p-arm is the shorter arm of a submetacentric chromosome. Q-arm is the longer one.

Question 6

During what phase of mitosis are chromosomes analyzed under a microscope?

Answer 6

metaphase. They become more condensed as it continues.

Question 7

What are balanced abnormalities?

Answer 7

novel rearrangement containing the net normal amount of genetic material. Normal phenotype, but reproductive risk

Question 8

What is an unbalanced abnormality?

Answer 8

arrangement associated with extra or missing genetic material. High likelihood of phenotypic abnormality.

Question 9

What is partial trisomy?

Answer 9

a structural abnormality that results in 3 copies of a particular chromosome segment.

Question 10

What is partial monosomy?

Answer 10

only one copy of a chromosome segment

Question 11

What does de novo mean?

Answer 11

new. (not from the parent)

Question 12

What does familial mean?

Answer 12

structural abnormalities that segregate through a pedigree in a balanced form, occasionally creating unbalanced offspring

Question 13

What does constitutional mean?

Answer 13

present in all cells of the body

Question 14

What does acquired mean?

Answer 14

arises in somatic cell of single tissue typically applied to cancer lineages

Question 15

What are Robertsonian translocations?

Answer 15

central fusions of the long arms of acrocentric chromosomes

Question 16

What are reciprocal translocations?

Answer 16

chromosomes swap pieces. Two breaks, reciprocal exchange of segments between two nonhomologous chromosomes. sometimes results in stable division if each piece ends up with a centromere and telomeric ends.

Question 17

What would be the chromosome number for a patient with a balanced robertsonian translocation?

Answer 17

45, because two chromosomes that used to be separate are now fused

Question 18

What is a pericentric inversion?

Answer 18

2 breaks in different arms of a chromosome. Inversion piece includes centromere

Question 19

What is a paracentric inversion?

Answer 19

2 breaks in same arm and a piece flips and reattaches upside down

Question 20

What is a n interstitial deletion?

Answer 20

two breaks in the same arm and piece is lost from chromosome

Question 21

Are deletions balanced or unbalanced changes?

Answer 21

unbalanced.

Question 22

What is a terminal deletion?

Answer 22

single break and loss of broken terminal segment. Telomeres heal and regenerate

Question 23

What are isochromosomes?

Answer 23

unbalanced abnormality that is the result of misdivision at the centromere during metaphase/anaphase. Division occurs transversely instead of longitudinally. You get two copies of the p arm in one chromosome and one with 2 q arms.
Causes a partial trisomy and a partial monosomy

Question 24

What is an important clinical example of isochromosomes?

Answer 24

Turner syndrome 46,X,i(Xq)

Down syndrome 46,,XY,i(21q)

Question 25

What is duplication?

Answer 25

small segment of chromosome is duplicated in one chromosome, resulting in partial trisomy.

Question 26

Is duplication a balanced change?

Answer 26

no

Question 27

Would you expect a phenotype abnormality in a person with a pericentric inversion?

Answer 27

no, inversions do not alter phenotype, but present a reproductive risk

Question 28

What would a t(9;22) cause?

Answer 28

translocation between 9 and 22 causes CML (chronic myelogenous leukemia)

Question 29

Which sex has a higher risk of nondisjunction?

Answer 29

female. usually nondisjunction errors are received from the mother

Question 30

Which trisomies are most likely to produce a live infant with an unbalanced karyotype?

Answer 30

21 most likely.

13 is possible, but very very low risk because pregnancies fail.

Question 31

Which trisomies are most likely to produce a live infant with an unbalanced karyotype?

Answer 31

21 most likely. 13 also, but results in much more pre-birth deaths