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BMS > Meiosis and Common Chromosomal Anomalies > Flashcards

Meiosis and Common Chromosomal Anomalies Flashcards

1
Q

Fertilization of a female oocyte (gamete) by male spermatocyte (gamete) reconstitutes the 46 chromosome number in the

A

Zygote (diploid, N = 23)

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2
Q

How are autosomes and sex chromosomes characterized?

A
  1. ) Size
  2. ) Centromere index
  3. ) Chromosome G-bright
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3
Q

What is the centromere index?

A

Length of p arm / total chromosome length

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4
Q

Low AT/GC ratio, rich in SINE repeats and Alu sequences, early replicating, contain “housekeeping genes”, not tissue specific, and rich in transcribed genes give

A

Bright G bands

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5
Q

Diploid cells replicate and divide into two identical diploid cells

A

Meiosis I

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6
Q

DNA cells replicate and the replicated homologous chromosomes establish connections (synapsis)

A

Prophase I

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7
Q

Homologous chromosome pairs are ordered in the middle of the cell

A

Metaphase I

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8
Q

There is chiasmata at the chromosome ends, and the homologous pairs migrate to opposite poles of the cell

A

Anaphase I

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9
Q

The formation of nuclei and two daughter cells

A

Interkinesis I

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10
Q

Separates sister chromatids and is made up of Prophase without DNA synthesis, metaphase, and anaphase, and results in 4 haploid cells

A

Meiosis II

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11
Q

When there is no separation of homologues between metaphase and anaphase

A

Non-disjunction Meiosis I

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12
Q

Non-disjunction in meiosis I will lead to

A

2 Disomic gametes and 2 monosomic gametes

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13
Q

When there is no separation of sister chromatids between metaphase and anaphase

A

Non-disjunction Meiosis II

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14
Q

Non-disjunction Meiosis II results in two normal gametes and

A

One disomic gamete and one nullisomic gamete

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15
Q

In Males, we see meiosis I followed by Meiosis II starting at puberty. Male meiosis allows for the development of

A

4 spermatids

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16
Q

In females, meiosis I begins early in intrauterine development and stops before

A

Birth “diplotene”

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17
Q

Only 20% of the 6-7 million original oogonia survive as primary oocytes that are arrested in

A

“Dictyotene” until puberty

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18
Q

With folliculogenesis, meiosis-I is completed with the extrusion of the 1st polar body at the time of

A

Ovulation

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19
Q

Completion of meiosis-II with the extrusion of the 2nd polar body occurs at

A

Fertilization

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20
Q

Female meiosis ends with

A

1 Mature oocyte and 2 lost polar bodies

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21
Q

Can be used to determine parental origin of chromosomes

A

Polymorphic CA-repeats

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22
Q

Polymorphic markers at the beginning of the p-arm or q-arm of the chromosome permits the differentiation of whether non-disjunction occurred in

A

Meiosis I or Meiosis II

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23
Q

Non-disjunction in meiosis I will be indicated by markers that are

A

Heterozygous close to the centromere

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24
Q

Non-disjunction in meiosis II will be indicated by markers that are

A

Homozygous close to the centromere

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25
Q

Chromosomal synapsis is driven by DNA homology resulting in a quadri-radial arrangement with 16 possible segregations of which only

A

2 are balanced (12%)

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26
Q

Leads to acentric/dicentric chromatids with duplications/deficiencies or genetic information

A

Recombination in inversion loop during meiosis I

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27
Q

All female are mosaic. A few patients with
non-random inactivation of the X chromosome
that carry an X-linked disorders or that are
Homozygous for the X-chromosome could
manifest

A

X-linked conditions

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28
Q

The random and clonal X-inactivation in females at blastocyst stage for gene dosage compensation with a male

A

Mary Lyon Hypothesis

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29
Q

Refers to the situation in which 2 copies of a chromosome come from the same parent, instead of 1 copy coming from the mother, and 1 copy coming from the father

A

Uniparental Disomy

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30
Q

Fertilization with hyperhaploid (disomic) gamete with
subsequent loss of the normally inherited chromosome from the other gamete (trisomy rescue) during mitosis causes 1-2% chromosomal mosaicism detected in

A

Placental samples

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31
Q

Determined by:
1) Degree of mosaicism
2) Genomic imprinting mechanisms in affected chromosomes
3) The non-Mendelian expression of monogenic disorders that map to that chromosome
4) by the combination of all these
factors?

A

Fetal phenotype

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32
Q

Changes in gene expression in response to the environment

A

Epigenetics

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33
Q

Reversible condensed chromatin conformation represses

A

Transcription

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34
Q

This regulatory mechanism of gene expression is also clinically relevant for placenta differentiation and function causing Intrauterine fetal growth restriction

A

Imprinting

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35
Q

Imprinting has been reported on chromosomes

A

7, 11 (Beckwith Wiedemann), 15 (Prader WIlli/ Angleman), and X (inactivation)

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36
Q

Allow for genetically unique newborns across generations with a 46 chromosome complement.

A

Sexual reproduction and Meiosis

37
Q

The consequence of random distribution of homologous chromosomes (8,388,608 possible combinations) together with the formation of Chiasmata among
non-sister chromatids during Meiosis with DNA crossing over events

A

Genetic Diversity

38
Q

A meiotic non-disjunction even leads to numerical chromosomal abnormalities in the

A

Zygote

39
Q

What are two sexual differentiation and sex-chromosome anomalies resulting from non-disjunction events?

A
  1. ) Turner Syndrome (45, X)

2. ) Klinefelter Syndrome (47, XXY)

40
Q

Affects 4% of all conceptus. Characterized by cystic hygroma, gonadal dysgenesis, and short stature

A

Turner Syndrome

41
Q

Affects 1 in 1,000 males, tall, hypogonadism,

gynecomastia, social dysfunctions. Mental Retardation associated with increasing numbers of X chromosomes in males

A

Klinefelter syndrome

42
Q

Affects 1 in 7,500 births with Heart/ CNS/ Renal

abnormalities, growth restriction, Micrognathia, Omphalocele, Equinovarus, Clenched hands

A

Edwards syndrome (47, XX, +18)

43
Q

Affects 1 in 20,000 births with IUGR, CL/P, CNS, Renal,

Heart, Omphalocele, Equinovarus, Polydactyly

A

Patau Syndrome (47, XY, +13)

44
Q

The most common genetic cause of mental retardation

A

Down Syndrome (47, XX, +21)

45
Q

Overexpression and interactions of multiple genes from chromosome 21 cause

A

Down Syndrome (47, XX, +21)

46
Q

A translocation resulting in an even exchange of genetic information with no genetic information extra or missing

A

Balanced translocation

47
Q

In a newborn, almond-shaped eyes with up slanting palpebral fissures, epicanthal folds, small dysplastic
ears, depressed nasal bridge with mid face hypoplasia, strabismus, and brushfield spots suggests

A

Down syndrome

48
Q

Brachycephaly, i.e. round head shape w/flattened occiput and excess nuchal skin, hypotonia,
atlantoaxial instability, joint laxity, shallow acetabular angle are also indicators of

A

Down Syndrome

49
Q

Affects 1 in 15,000 liveborn with morbid obesity, short stature, hypogonadism, mental retardation, and hiyperphagia

-Due to a paternal deficiency (deletion) of the 15q11-13 and imprinting of the maternal chromosome

A

Prader-Willi Syndrome

50
Q

The affected have severe mental retardation, absent speech jerky gait, protruding tongue, and inappropriate laughter

-Due to a maternal deficiency of the 15q11-13 loci (deletion) and imprinting of the paternal chromsome

A

Angleman Syndrome

51
Q

No separation of sister chromatids; disjunction of homologues results in segregation of alleles

A

Meiosis I

52
Q

There is no S phase in

A

Meiosis II

53
Q

Nullisomic gametes yield

-Lethal except for X chromosome

A

Monosomic zygotes

54
Q

Disomic gametes yield

-Lethal except for X, Y, and a few small autosomes (13, 18, 21)

A

Trisomic Zygotes

55
Q

Create partial trisomy/monosomy syndromes

A

Balanced translocations

56
Q

Imprinting will result in disease if the individual has

A

Uniparental Disomy (ex: Prader-Willi and Angleman syndromes)

57
Q

Result from a uniparental disomy of chromosome 15

A

Prader-Willi and Angleman syndromes

58
Q

Characterized by chromosomal synapse driven by DNA homology resulting in a quadrivalent arrangement with 16 possible segregations, of which only alternate segregation can lead to 2 balanced gametes (12%)

A

Balanced translocation

59
Q

Phenotypically normal parents with pericentric inversion can have children with

A

deletions/duplications (5-10% risk)

60
Q

Results in 4 chromosomes coming together in synapses in prophase I

A

Balanced translocation

61
Q

All the cells in our body have 46 chromosomes, the purpose of meiosis is to create gametes that only have

A

23

62
Q

In G-banding, the bright bands are the ones rich in

A

Genes

63
Q

The most common mutations in humans

A

Chromosomal abnormalities

64
Q

What percentage of 1st trimester spontaneous pregnancy losses have chromosomal abnormalities?

A

50%

65
Q

If it occurs in the egg, nondisjunction is more common in

A

Meiosis I

66
Q

If it occurs in the sperm, non-disjunction is more common in

A

Meiosis II

67
Q

In females, meiosis-I begins early in intrauterine development and stops in the 4th stage of prophase I known as

A

Diplotene

68
Q

Only 20% of the 6-7 million original oogonia survive as primary oocytes that are arrested in

A

Dictyotene (part of prophase I)

69
Q

The polar body from meiosis I with 2 sister chromatids

A

1st Polar body

70
Q

The polar body from meiosis II with 1 sister chromatid

A

2nd Polar body

71
Q

When one cell line is normal and the other cell line is trisomic

A

Mosaic form

72
Q

Phenotypically normal parents with pericentric inversions can have children with

A

Deletions/duplications

73
Q

How many Barr bodies are there?

A

Barr bodies = # X-chromosomes - 1

74
Q

A disorder that affects males because they do not have an extra X chromosome to compensate

A

Duchenne Muscular Distrophy

75
Q

Duchenne muscular dystrophy should not appear in females unless there is a skewing of the

A

X inactivation centers

76
Q

When 2 chromosomes are inherited from the same parent

-enables AR diseases to appear when only one parent is a carrier

A

Uniparental Disomy

77
Q

3% of all down syndrome cases result from parents that have a

A

Balanced translocation

78
Q

The robertsonian translocation 45, XX, der(21;21) has a recurrence risk of

A

100%

79
Q

The rate of down syndrome identification after 20 weeks of gestation is

A

1 in 2000

80
Q

How many americans have down syndrome?

A

400,000

81
Q

Free fetal DNA in maternal circulation can also be used for

A

Aneuploidy screening

82
Q

Integrates image of fetus with biochemical maternal age

A

Sequential Integrated Screening Test

83
Q

Step 1 of the sequential integrated screening test occurs in trimester 1 and step 2 in trimester 2. How efficient is the test for detecting down syndrome?

A

98%

84
Q

a medical procedure used in prenatal diagnosis of chromosomal abnormalities and fetal infections. The fetal DNA is examined for genetic abnormalities.

-The most common reason to have this test is to determine whether a baby has certain genetic disorders or a chromosomal abnormality, such as Down syndrome.

A

Amniocentesis

85
Q

A test made in early pregnancy to detect congenital abnormalities in the fetus.

-A tiny tissue sample is taken from the villi of the chorion, which forms the fetal part of the placenta.

A

Chorionic Villous Sampling

86
Q

What is the frequency for chromosomal abnormalities for:

  1. ) Abnormal complement of sex chromosomes
  2. ) Autosomal trisomy
  3. ) Translocation (mostly balanced)
  4. ) Total
A
  1. ) 1/500
  2. ) 1/700
  3. ) 1/400
  4. ) 1/150
87
Q

What is the procedure related risk for US-guided diagnostic amniocentesis?

A

1 in 300

88
Q

A recombination of an inversion creates an

A

Acentric/dicentric chromosome

89
Q

Balanced translocations create

A

Partial monosomy/trisomy syndromes

BMS (62 decks)

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