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Molecules to Medicine Unit 2 > Chromosome Abnormalities I, II and III > Flashcards

Chromosome Abnormalities I, II and III Flashcards

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1
Q

In meiosis, after DNA replication, cells undergo ___________

A

Two successive rounds of chromosome segregation

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2
Q

In meioses, chromosome content is reduced from __________ in the first meiotic division and from __________ in the second meiotic division.

A

4n to 2n and 2n to n

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3
Q

Reciprocal recombination events occur during __________

A

Prophase I

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4
Q

On average, ______ crossovers occur on each chromosome.

A

2-3

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5
Q

A genetic consequence of meiosis is reduction is chromosome number from _________ to _________

A

Diploid to haploid

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6
Q

Meioses II is much like __________

A

A mitotic divisions

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7
Q

Reciprocal recombination events between maternal and paternal sister chromatids generate ___________

A

Chiasmata

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8
Q

What is a metacentric chromosome?

A

The centromeres is located in the middle of the chromosome such that the two chromosome arms are approximately equal in length.

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9
Q

What is a submetacentric chromosome?

A

The centromeres is slightly removed from the center.

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10
Q

What is a acrocentric chromosome?

A

The centromere is near one end of the chromosome.

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11
Q

In the two hit theory, the first hit is _____________, caused either by a lack of chasm or their mislocalizations, resulting in a chromosome more susceptible to possible nondisjunction.

A

Diminished Recombination

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12
Q

The second hit of the two hit theory is the ability of oocytes to successfully ____________ in the presence of unfavorable recombination events is through to diminish over time

A

complete chromosome segregation

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13
Q

A second model suggests that the degradation of ________ over the course of the extended meiosis I arrest in oocytes results in the precocious separation of homologs

A

Cohesin

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14
Q

The age related degradation of cohesion established during detail development has been postulated to allow ____________

A

The movement of the chiasmata towards the ends of the homologs

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15
Q

Characteristics of Trisomy 18: Edward’s Syndrome.

A

Mental retardation and hand clenching

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16
Q

Characteristics of Trisomy 13: Patau syndrome

A

Facial clefts, hand clenching, mental retardation

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17
Q

Characteristics of 47, XXY: Klinefelter syndrome

A

Tall stature, hypogonadism, sterility, language impairment

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18
Q

Characteristics of 45, X-Turner Syndrome

A

Short stature, webbed neck, edema of hands and feet, broad, shield like test, narrow hips, failure of ovarian maintenance.

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19
Q

When does germ line mosaicism occurs?

A

Exists when a somatic mutation occurs early in development and generates mutant sub-population of germ cells.

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20
Q

Most children with Down Syndrome have 47 chromosomes, the extra member being a small ___________

A

Acrocentric chromosome

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21
Q

The meiotic error responsible for trisomy 21, usually occurs during maternal meioses, predominantly in _________, but about 10% of cases occur in paternal meioses, usually __________

A

Meioses I and Meiosis II

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22
Q

Chromosomal rearrangement require two ___________ and can be induced by a variety of DNA damaging agents

A

DNA double strand breaks

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23
Q

Structural rearrangements can be __________ and can also lead to further rearrangement during meiosis.

A

inherited

24
Q

What are balanced structural rearrangements?

A

Normal complements of chromosomal material with no loss of genetic material

25
Q

What is an inversion?

A

A balanced structural rearrangement and occurs when one chromosome undergoes two double strand breaks of the DNA backbone and the intervening sequence is inverted prior to the rejoining of the broken ends

26
Q

Paracentric inversions _________ the centromere

A

Exclude

27
Q

Pericentric inversions ___________ the centromere

A

include

28
Q

What is a reciprocal translocation?

A

Results from the breakage and rejoining of non-homologous chromosomes, with a reciprocal exchange of the broken segments

29
Q

Carriers of reciprocal translocations have increased risk of producing ___________

A

Unbalanced gametes

30
Q

When the chromosomes of a carrier of a balanced reciprocal translocation pair at meiosis, a ___________ is formed.

A

Quadravalent

31
Q

The quadravalent structure formed by reciprocal translocation can lead to three segregations. What are they?

A
  1. Alternate 2. Adjacent 1 (leads to unbalanced gametes) 3. Adjacent 2 (lead to unbalanced gametes)
32
Q

What is a robertsonian translocation?

A

The fusion of two acrocentric chromosomes within their centromeric regions, resulting in the loss of both short arms

33
Q

What is an unbalanced deletion?

A

Loss of genetic information that can arise from simple chromosome breakage and rejoining, unequal crossing over between misaligned homologous chromosomes or sister chromatids or by abnormal segregation or a balanced translocation or inversion

34
Q

A deletion can be ________ or ___________

A

terminal, interstitial

35
Q

__________ is generally less harmful than an unbalanced deletion.

A

Unbalanced duplication

36
Q

What is an isocrhomosome?

A

A chromosome in which one arm is missing and the other is duplicated in a mirror image fashion, possibly occurring through an exchange involving one arm of a chromosome and its homolog at the proximal edge of the arm, adjacent to the centromere.

37
Q

A small percentage of ___________ patients have 21q21q isochromosome

A

Down’s Syndrome

38
Q

What is DiGeorge syndrome?

A

Example of contiguous gene syndrome, which is an abnormal phenotype caused by over-expression or loss of neighboring genes. Causes serious heart defect. Caused by a deletion on chromosome 22.

39
Q

What is Velocardiofacial syndrome?

A

Example of contiguous gene syndrome, which is an abnormal phenotype caused by over-expression or loss of neighboring genes. Causes cleft palate and septal defects. Caused by a deletion on chromosome 22.

40
Q

To be completely stable, a rearranged chromosome much have _________ and __________

A

Functional centromere and two telomeres

41
Q

A ring chromosome is likely to be formed when a chromosome undergoes ____________ and reunite

A

Two breaks

42
Q

The molecular basis of imprinting is based on __________

A

The allele-specific methylation of CpG dinucleotides in the promoter regions

43
Q

Hypermethylation in gene silencing, may directly inhibit transcription by ____________ or _________

A

Repelling transcription factors or actively recruit factors that repress transcription.

44
Q

What are the three characteristics of imprinted genes?

A
  1. These genes tend to be clustered together rather then spread throughout the entire genome 2. These clusters contain both maternally and paternally imprinted genes. 3. The imprinted genes encode both proteins and non-coding RNA’s
45
Q

DNA demethylation reactivates gene expression and erases the parental methylation pattern in developing gametes. Demethylation could result from the _____________ or indirectly through ___________

A

inhibition of the maintenance methyltransferase; inactivation of chromatin-remodeling proteins

46
Q

Erasure and resetting of the imprint appear to occur at imprinting centers, which contain non-coding DNA sequences that bind impinged RNA transcriptions, called ___________ and recruit DNA methyltransferase complex that methylate CpG islands located near the IC on the same chromosome (cis).

A

BD transcripts.

47
Q

In 70% of Prader Willi cases, the syndrome is the result of a deletion invoking the long arm of chromosome _________ occurring on the homolog inherited from the _________

A

15; father

48
Q

Angelmen’s syndrome has a same deletion on chromosome _____________ but on the __________ homolog

A

15; maternally-derived

49
Q

_____________ commonly occurs when a trisomic conceptus loses one of its extra chromosomes due to mitotic nondisjunction in early gestation

A

Uniparental disomy

50
Q

A young child present to you office with a genotype 46XY del (15) (q11q13) on the maternal chromosome. Which of the following clinical features would be most consistent with the patient’s genotype?

A

Seizures - if the is child has a material deletion of chromosome 15, that have Angelman’s Syndrome,

51
Q

In adjacent 1 segregation, homologous centromeres go to __________

A

different daughter cells

52
Q

In adjacent 2 segregation, both homologs go to __________

A

The same daughter cell

53
Q

Paternally and maternally derived homologous chromosomes synapses along their entire length to form bivalent structure during which phase of meiosis?

A

Prophase I

54
Q

Paternal error in _________ results in 47XXY Klinesfelter’s.

A

Meiosis I

55
Q

46 X i(Xd) indicates __________

A

Female with isochromosome for the long arm of X

56
Q

What is the genotype of a male with fragile X?

A

46, Y fra(x) (q27.3)

57
Q

What percentage of offspring from an individual whose genotype is i21 will be abnormal?

A

100%; i21 is the isochromosome for 21 meaning that the long arms of 21 has fused and it is impossible for the gamete to be haploid. 50% of the gametes will not receive a 21 and the other 50% will get the isochromosome and be trisomic for 21

Molecules to Medicine Unit 2 (18 decks)

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