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BIO207 > Chromosomal Rearrangements > Flashcards

Chromosomal Rearrangements Flashcards

1
Q

What are the two types of events that reshape genomes?

A

Rearrangements and changes in chromosome numbers

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2
Q

What are rearrangements?

A

DNA sequences reorganized within one or more chromosome

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3
Q

What is nondisjunction?

A

The failure of chromosomes and sister chromatids to properly separate during cell division

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4
Q

What is the euploid number?

A

Number of complete sets of chromosomes in an individual (e.g., n, 2n, 3n)

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5
Q

What is aneuploid number?

A

When cells contain a number of chromosomes that are not euploid

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6
Q

What is the result of nondisjunction in germ-line cells?

A

Aneuploid gametes that can produce aneuploid zygotes

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7
Q

What causes nondisjunction in meiosis I?

A

Failure of homologs to separate

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8
Q

What gametes are produced from nondisjunction of meiosis I?

A

n+1 or n-1

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9
Q

What kind of offspring does fusion of n+1 or n-1 gametes with normal (n) gametes produce?

A

Trisomic (2n+1) or monosomic (2n-1)

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10
Q

What causes nondisjunction in meiosis II?

A

Failure of sister chromatids to separate normally

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11
Q

Among the 4 gametes produced by meiosis, how many are affected by nondisjunction of meiosis II?

A

2

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12
Q

What are the characteristics of gametes produced by meiosis II nondisjunction?

A

2 are normal (n), one is n+1, one is n-1

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13
Q

What type of offspring can be produced by meiosis II nondisjunction

A

50% normal diploid, 25% trisomic, 25% monosomic

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14
Q

What do changes in gene dosage cause?

A

Imbalance of gene products from the affected chromosome relative to the unaffected chromosomes.

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15
Q

How are humans affected by aneuploidy?

A

Humans are very sensitive to gene dosage and aneuploids usually don’t survive

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16
Q

What type of aneuploidies do we see in humans?

A

Autosomal trisomies of chromosomes 13, 18, 21; no autosomal monosomies
Multiple sex-chromosome trisomies and one sex-chromosome monosomy

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17
Q

What syndrome is caused by trisomy 13?

A

Patau syndrome

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18
Q

What are the characteristics of patau syndrome ?

A

Mental retardation and developmental delay, possible deafness, major organ abnormalities, early death

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19
Q

What syndrome is caused by trisomy 18?

A

Edwards syndrome

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20
Q

What are the characteristics of Edwards syndrome?

A

Mental retardation and developmental delay, skill and facial abnormalities, early death

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21
Q

What syndrome is caused by trisomy 21?

A

Down syndrome

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22
Q

What are the characteristics of down syndrome?

A

Mental retardation and developmental delay, characteristic facial abnormalities, short stature, variable life span

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23
Q

What syndrome is caused by XYY?

A

Jacob syndrome

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24
Q

What are the characteristics of Jacob syndrome?

A

Tall stature, possible reduction but not loss of fertility, no impact on mental capacity

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25
Q

What syndrome is caused by XXX?

A

Triple X syndrome

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26
Q

What are the characteristics of triple X syndrome?

A

Tall stature, possible reduction of fertility, menstrual irregularity, no impact on mental capacity

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27
Q

What happens to the risk of down syndrome as a mother gets older?

A

Increases

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28
Q

A portion of chromosome 21 is correlated with the majority of Down syndrome symptoms?

A

DSCR (down syndrome critical region)

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29
Q

What gene makes a major contribution to Down syndrome?

A

DYRK, has a homolog known to produce dosage-sensitive learning defects in mice

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30
Q

How is Turner syndrome explained?

A

In XO embryos, the single copy of the gene SHOX, which is not inactivated by dosage compensation, is insufficient to direct normal development

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31
Q

What is chromosomal mosaicism?

A

When someone has two or more genetically different sets of cells

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32
Q

What is uniparental disomy?

A

When both copies of a homologous chromosome pair arise from the same parent.

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33
Q

What two conditions was uniparental disomy first identified in?

A

Angelman syndrome, Prader-Willi syndrome

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34
Q

What is a rare mechanism for uniparental disomy?

A

The same chromosome undergoes nondisjunction in both sperm and egg. Fertilization occurs with one of the gametes contributing two copies of the chromosome and the other gamete does not contribute a copy.

35
Q

What is a more common mechanism for uniparental disomy?

A

Nondisjunction occurs in one parent, resulting in an n+1 gamete.
This unites with a normal gamete to produce a trisomic zygote.
Trisomy rescue occurs.
If the two copies retained by the zygote are from the same parent, uniparental disomy results.

36
Q

What is trisomy rescue?

A

One copy of the trisomy chromosome is randomly ejected in one of the first mitotic divisions after fertilization

37
Q

What is polyploidy?

A

Presence of three or more sets of chromosomes in the nucleus of an organism

38
Q

What is autopolyploidy?

A

Polyploidy resulting from duplication of chromosome sets within a species

39
Q

What is allopolyploidy?

A

Polyploidy resulting from combining the chromosome sets of different species

40
Q

What two mechanisms most commonly cause autopolypoloidy?

A

Meiotic nondisjunction leading to a diploid rather than haploid gamete
Mitotic nondisjunction that doubles chromosome number

41
Q

What are some consequences of polyploidy?

A

Decreased fertility, hybrid vigor?

42
Q

What is hybrid vigor?

A

More rapid growth, increased fruit and flower production, improved disease resistance

43
Q

What is a chromosome break point?

A

The location at which both DNA strands are severed during chromosome breakage.

44
Q

What can lead to a terminal deletion?

A

Detachment of all or part of one chromosome arm

45
Q

When might a broken chromosome fragment be lost during cell division?

A

If it is acentric (i.e., lacks a centromere)

46
Q

What are partial deletion heterozygotes?

A

Organisms with one normal and one terminally deleted chromosome

47
Q

What is cri-du-chat syndrome?

A

Infants have a cat-cry sound

48
Q

What causes cri-du-chat syndrome?

A

Partial deletion heterozygotes who lost 5p15.2-5p15.3

49
Q

What is an interstitial deletion?

A

The loss of an internal portion of a chromosome

50
Q

What causes interstitial deletion?

A

Two chromosome breaks

51
Q

What causes WAGR syndrome?

A

Interstitial deletion of multiple genes on chromosome 11

52
Q

What does unequal crossover cause?

A

Partial duplication on one homolog and partial deletion on the other?

53
Q

What is a partial duplication heterozygote?

A

An organism with one normal and one duplication homolog

54
Q

What is a partial deletion heterozygote?

A

An organism with one normal and one deleted homolog.

55
Q

When does unequal crossover most commonly occur?

A

When repetitive regions of homologs misalign.

56
Q

What causes Williams-Beuren syndrome?

A

Partial deletion heterozygotes for the segment of chromosome 7 that contains duplicated copies of a gene called PMS (PMSA and PMSB).
Unequal crossover leads to one nonfunctional hybrid PMSA- PMSB gene

57
Q

How can large deletions or duplications be detected?

A

By microscopy that reveals altered chromosome banding patterns

58
Q

How can microdeletions and microduplications be detected

A

Molecular techniques like FISH

59
Q

What is another microscopic approach to detect regions of chromosome duplication or deletion?

A

Microscopic observation during prophase I

60
Q

What causes an unpaired loop?

A

A large deletion or duplication creates an area of mismatch

61
Q

What is pseudodominance?

A

When a recessive allele is unmasked by a deletion that removes the dominant allele on the homolog

62
Q

What is chromosome inversion?

A

Reattachment at the wrong end

63
Q

What is chromosome translocation?

A

Reattachment to a nonhomologous chromosome

64
Q

What are the two possible types of chromosome inversion?

A

Paracentric and pericentric

65
Q

What is paracentric inversion?

A

Centromere is outside of the inverted region

66
Q

What is pericentric inversion?

A

Centromere is within the inverted region

67
Q

What are inversion heterozygotes?

A

Individuals with one normal and one inverted homolog

68
Q

What does the alignment of a normal chromosome with its inverted homologs result in?

A

Inversion loop

69
Q

What does crossing over within the inversion loop result in?

A

Deletions and duplications in the recombinant chromosomes

70
Q

What does crossing over within a paracentric inversion result in?

A

Dicentric chromosome and an acentric fragment (which is lost)

71
Q

What does crossing over within a pericentric inversion result in??

A

Duplicated and deleted regions in both of the recombinants

72
Q

What are the three genetic implications of recombination in inversion heterozygotes?

A
  1. The probability of crossover within the inversion loop is proportional to the size of the loop
  2. Inversion suppresses the production of recombinant chromosomes (crossover suppression)
  3. Fertility may be altered if an inversion heterozygote carries a very large inversion
73
Q

What is chromosome translocation?

A

When broken ends of nonhomologous chromosomes are reattached

74
Q

What are nonreciprocal translocations?

A

A piece of one chromosomes is translocated to a nonhomolog and there is no reciprocal event

75
Q

What are reciprocal balanced translocations?

A

Pieces of two nonhomologs switch places

76
Q

What are Robertsonian translocations?

A

Fusion of two nonhomologous chromosomes

77
Q

What happens in heterozygotes for reciprocal balanced translocations?

A

None of the four chromosomes has a fully homologous partner.
A cross-like structure is formed as metaphase I of meiosis and two patterns of segregation are possible.

78
Q

What is alternate segregation?

A

The two normal chromosomes move to one pole of the cell and the two translocated chromosomes to the other.

79
Q

What is adjacent-1 segregation?

A

One normal and one translocated chromosome move to each pole of the cell

80
Q

What is the very rare adjacent-2 segregation?

A

Homologous centromeres move together to each pole of the cell

81
Q

Describe the gametes produced by alternate segregation?

A

Have a full haploid set of genes

82
Q

Describe the gametes produced by adjacent segregation.

A

Each gamete contains two copies of some genes and the complete absence of others.

83
Q

Where are translocation heterozygotes semi-sterile?

A

Only alternate segregation leads to normal gametes.

84
Q

What happens if two pairs of chromosomes fuse by Robertsonian translocation?

A

Number of chromosomes drops to 2n-2

BIO207 (9 decks)

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