Chromosomal Abnormalities

Question 1

Which is the stabilising histone?

Answer 1

H1

Question 2

What is the term for chromatin switching back and forth between active and inactive?

Answer 2

Epigenetic modification

Question 3

Which 2 processes help with chromatin activation?

Answer 3

DNA demethylation and histone acetylation

Question 4

Which 2 processes help with chromatin deactivation?

Answer 4

DNA methylation and histone deacetylation

Question 5

What does acrocentric mean?

Answer 5

The p arm is small in comparison to the q arm.

Question 6

As the number of the chromosome increases, the size of the chromosome…
Except for…

Answer 6

decreases, except chromosome 22 is bigger than chromosome 21

Question 7

What groups can chromosomes be split into and which are acrocentric?

Answer 7

groups A-G, groups D and G are acrocentric

Question 8

What does a dark band on a chromosome mean?

Answer 8

AT rich, gene poor

Question 9

What does a light band on a chromosome mean?

Answer 9

GC rich, gene rich

Question 10

What are the different staining methods for chromosomes?

Answer 10

solid staining, G banding, C banding (centromeres) and Q banding (fluorescent)

Question 11

What are constitutional abnormalities?

Answer 11

abnormalities that have been present since birth

Question 12

Define aneuploidy

Answer 12

The loss or gain of whole chromosomes.

Question 13

Define trisomies

Answer 13

Having 3 copies of a particular chromosome.

Question 14

Which 3 trisomies are the only ones compatible with life and which syndromes do they relate to?

Answer 14

21: Down syndrome
13: Patau syndrome
18: Edwards syndrome

Question 15

Define monosomies

Answer 15

Having only 1 copy of a particular chromosome.

Question 16

What is the only monosomy compatible with life?

Answer 16

monosomy X
Turner syndrome (45,X) - only affects females

Question 17

Define polyploidy

Answer 17

Sets of chromosomes greater than the normal diploid number.

Gain of a whole haploid set(s) of chromosomes

Question 18

Write the karyotype for triploidy

Answer 18

69,XXX

Question 19

Define mosaicism

Answer 19

Cells within the same person have a different genetic makeup.

Question 20

What is anaphase lag?

Answer 20

Chromosomes get left behind at cell division due to defects in the spindle function or attachment.

Question 21

What is hypotonia and what is it a sign of?

Answer 21

floppy baby: low muscle tone

Down syndrome

Question 22

What do patients with Down Syndrome have an increased prevalence of?

Answer 22

leukaemia and early Alzheimers

Question 23

What features define Edwards syndrome?

Answer 23

small lower jaw, low-set ears, rocker-bottom feet and overlapping fingers

Question 24

Where does with error usually occur that causes Edwards syndrome and what is the average lifespan?

Answer 24

maternal meiosis II error

lifespan: 5-15 days

Question 25

What are the features of Patau syndrome?

Answer 25

polydactyly, failure of forebrain to develop, facial defects and the majority die as neonates

Question 26

What are the features of Turner syndrome?

Answer 26

puffy feet, short stature, heart defects, infertility, redundant skin on back of neck and absent paternal X chromosome in most cases

Question 27

How do X chromosomes vary from autosomes?

Answer 27

only one X chromosomes is ever active in a human cell

Question 28

What are PAR1 and PAR2?

Answer 28

Short, pseudo-autosomal regions that X and Y chromosomes have in common.

Question 29

What are PAR1 and PAR2 needed for?

Answer 29

Pairing in meiosis

Question 30

What is Uniparental Disomy (UPD)?

Answer 30

presence of homologous chromosomes from only one parent in a cell

Question 31

Define isodisomy

Answer 31

2 identical chromosomes from one parent present

Question 32

Define heterodisomy

Answer 32

2 homologous chromosomes from one parent present

Question 33

What is it called when only part of the chromosome is involved in UPD?

Answer 33

segmental UPD

Question 34

How do you get acquired UPD?

Answer 34

when mitosis goes wrong in yourself (not the parents)

Question 35

How many histones make up the unit that DNA wraps around?

Answer 35

8 (octamer)

Question 36

What is genomic imprinting?

Answer 36

Epigenetic phenomenon by which certain genes are expressed dependent upon their parent of origin. If an allele is imprinted then it is silenced.

Question 37

What are the 4 ways in which UPD can arise?

Answer 37

trisomy rescue, monosomy rescue, gamete complementation and mitotic error

Question 38

What are reciprocal translocations?

Answer 38

The exchange of genomic material between 2 non-homologous chromosomes.

Question 39

What are the features of reciprocal translocation?

Answer 39

usually unique to a family, produce balanced and unbalanced gametes and if formed from meiotic disjunctions then quadrivalents form before segregation

Question 40

What are Robertsonian translocations?

Answer 40

Translocation caused by breaks at or near the centromeres of two acrocentric chromosomes. The reciprocal exchange of parts gives rise to one large chromosomes and one extremely small chromosome that may be lost. Leaves only 45 chromosomes since 2 have fused together.

Question 41

Do Robertsonian translocations affect the phenotype?

Answer 41

Not directly because the only genes lost are on the short arm which are common to many chromosomes and therefore will still be present within the cell.

Question 42

How can chromosome deletions occur?

Answer 42

From uneven pairing and recombination in meiosis.

Question 43

Can chromosome deletions be balanced?

Answer 43

No | They are always unbalanced because genetic material is lost.

Question 44

What tests would we do for prenatal aneuploidy screening?

Answer 44

FISH probes for common aneuploidies (quick) and full karyotype (slow)

Question 45

When and how can non-invasive prenatal testing occur?

Answer 45

using foetal DNA in maternal blood at 9 weeks gestation