Chromosome heteromorphisms

Question 1

Detailed DNA measurements by flow cytometry or micro- densitometry reveal that all chromosomes show interindividual variation in DNA content, which is heritable. Which chromosomes have the least and most variation.

Answer 1

Y - most variation
X - least variation

Question 2

The most obvious differences in the appear- ance of the chromosomes can be seen under an oil-immersion lens in at least 30% of the population. Such differences are called ____ and are examples of _____, discontinuous genetic variants present in 1% or more of the population).

Answer 2

heteromorphisms; genetic polymorphisms

Question 3

Size polymorphisms usually involve _____, and the degree of variation shows a ____.

Answer 3

Repetitive;normal distribution

Question 4

Four main groups of chromosome heteromorphisms are known including ____.

Answer 4

size of Yq
size of centromeric heterochromatin
satellite polymorphisms
fragile sites.

Question 5

Commonest chromosomal polymorphism.

Answer 5

Size of Yq

Question 6

The long arm of the Y contains ____ and fluoresces intensely under ultraviolet light with dyes such as quinacrine (Q-banding). This fluorescent region may be visible in an ____ nucleus and is referred to as ____ .

Answer 6

non-transcribed repetitive DNA; interphase; Y-chromatin

Question 7

About ___ percent of clinically normal males have a Y that is obviously longer or shorter than usual

Answer 7

10%

Question 8

Variations in the size of the centromeric heterochromatin are relatively frequent for chromosomes ____.

Answer 8

1, 9 and 16

Question 9

ariation in size of the satellites and in the degree of intensity with which they stain by Q-banding may be seen for the ____.

Answer 9

acrocentric chromosomes 13, 14, 15, 21 and 22

Question 10

Causes of satellite polymorphisms in acrocentric chromosome

Answer 10

repetitive DNA
Varying number of ribosomal genes
Differences in DNA content

Question 11

Differences in the DNA content causing satellite polymorphism in acrocentric chromosome is brought about by?

Answer 11

Unequal crossing over resulting from mispairing during meiosis at sites of repetitive DNA

Question 12

These are secondary constrictions that may be particularly liable to chromatid breaks.

Answer 12

Fragile sites

Question 13

There are at least ___ common fragile sites, which can be induced at low levels in all individuals by _____ and which usually involve both homologues.

Answer 13

89; aphidicolin

Question 13

Rare autosomal fragile sites, which usually involve only one homologue, show ____ inheritance.

Answer 13

Mendelian

Question 14

In addition to the 89 common fragile sites, ____ rare fragile sites have been described, which collectively occur in about ____ of the population. Most of these are induced by ____ agents in culture and almost all are autosomal

Answer 14

30; 5%; antifolate

Question 15

Most of the rare autosomal fragile sites which show Mendelian inheritance are not associated with clinical abnormalities except for ____.

Answer 15

X chromosomal fragile site at Xq27.3

Question 15

The molecular basis of fragile sites appears to involve tracts of ____ that have been amplified beyond a critical threshold.

Answer 15

trinucleotide repeats

Question 16

X chromosomal fragile site at Xq27.3 is associated with ____.

Answer 16

Mental handicap

Question 17

These variations involve repetitive DNA and include transposable elements and gene families.

Answer 17

Copy number variation

Question 18

Copy number variations vary from large segmental duplications up to several Mb in size, to smaller copy number variants. Most appear to have no phenotypic effect, despite being important in initiating ____ through _____.

Answer 18

chromosome rearrangements; non-allelic homologous recombination

Question 19

These submicroscopic deletions and duplications can be identified by ___.

Answer 19

high-resolution aCGH