Chromosomes and Disease

Question 1

Cytogenetics definition

Answer 1

study of chromosomes

Question 2

When is most clinical analysis of chromosomes done?

Answer 2

Metaphase;

when chromosomes are condensed

Question 3

G banding definition

Answer 3

visual inspection of chromosomes stained or labeled using dyes or fluorescent molecules;
Giemsa is US standard

Question 4

How does the staining of chromosomes work?

Answer 4

Stains AT enriched regions;

genes are usually GC rich so light bands correspond to the regions of the chromosome with higher density of genes

Question 5

How many bases does each band represent?

Answer 5

5-10 million bases on low resolution of chromosomes

Question 6

Centromere definition

Answer 6

contain repetitive sequences and serve as the attachment point for the machinery that separates the chromosomes

Question 7

Metacentric

Answer 7

centromere near middle of chromosome

Question 8

Submetacentric

Answer 8

centromere located towards one end of the chromosome; results in short arm at the top (p arm) and long arm at the bottom (q arm)

Question 9

Acrocentric

Answer 9

centromere is very close to one end of the chromosome

Question 10

Telomeres

Answer 10

found at ends of chromosomes;

protect the chromosomes from getting too short

Question 11

System for naming bands on chromosomes

Answer 11

• First part of name is the number of the chromosome followed by the arm (p or q)
• next number designates the region on the arm followed by the band number in that region;
  (ex: 14q32 - q arm of chromosome 14, region 3, band 2)

Question 12

Karyogram

Answer 12

organized image of a patient’s chromosomes

Question 13

Karyotype

Answer 13

describes the total number of chromosomes, identifies the sex chromosomes, and specifies any numeric or structural abnormalities

Question 14

Two classes of chromosomal abnormalities

Answer 14

Numerical abnormality;

Structural abnormality

Question 15

Numerical abnormality

Answer 15

changes in chromosome number from usual 46

Question 16

Structural abnormality

Answer 16

changes that affect how a chromosome is organized

Question 17

Trisomy (numerical abnormality)

Answer 17

there is an extra copy of a chromosome;

1-3% of pregnancies, 15-20% of chromosomal abnormal spontaneous abortions

Question 18

Monosomy (numerical abnormality)

Answer 18

there is a missing chromosome

Question 19

Translocation (structural abnormality)

Answer 19

parts of two chromosomes are exchanged

Question 20

Reciprocal translocation (structural abnormality)

Answer 20

parts of two chromosomes are exchanged in a balanced manner;

phenotypically normal unless break is in middle of the gene

Question 21

Euploidy

Answer 21

loss or gain of entire chromosome set;

69 triploid, 92 tetraploid

Question 22

Aneuploidy

Answer 22

loss or gain of less than entire chromosome set;

monosomy, trisomy

Question 23

Mosaicism

Answer 23

presence of more than 1 cell line;

often results as a function of trisomy rescue

Question 24

Synaptonemal complex

Answer 24

protein structure that forms mediating chromosome pairing

Question 25

Chiasma

Answer 25

physical points along chromosome where crossing over has occurred

Question 26

Recombination is essential...

Answer 26

avg 50 chiasmata in male meiosis; >1 chiasma/chromosome arm is required for normal segregation; recombination decreases near centromeres and increases near telomeres

Question 27

What are two causes of aneuploidy in meiosis and mitosis

Answer 27

Nondisjunction and anaphase lag

Question 28

Nondisjunction

Answer 28

failure of chromatids (during mitosis or meiosis II) or chromosomes (during meiosis I) to separate at anaphase

Question 29

Anaphase lag

Answer 29

failure of a chromatid of chromosome to attach to the spindle and segregate into a daughter cell

Question 30

Pseudoautosomal regions (PAR)

Answer 30

at x y of p arm, and q arm; recombination in these regions is a challenge due to size difference; leads to significant number of aneuploidy