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CYTOGENETICS > CHROMOSOME ABNORMALITIES > Flashcards

CHROMOSOME ABNORMALITIES Flashcards

1
Q

typical number of chromosomes in a human cell

A

46: 23 pairs

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2
Q

Types of Chromosomal Abnormalities

A
  1. Constitutional Abnormalities
  2. Acquired or Somatic Abnormalities
  3. Numerical Anomalies
  4. Structural Anomalies
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3
Q

Refers to anomalies that are inborn and have been always present in the embryo

A

Constitutional Abnormalities

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4
Q

Developed due to exposures, habits, or malignancies

A

Acquired or Somatic Abnormalities

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5
Q
  • Happens when the number of chromosomes in a somatic cell is not 46
  • If individual chromosomes have extra, missing, or rearranged genetic material
  • Account for 50% of spontaneous abortions but only 0.65% of newborns are born with these abnormalities
A

Numerical Abnormalities

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6
Q
  • Presence of extra sets of chromosomes
A

Polyploidy

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7
Q

an individual who has 3 sets or copies of chromosomes

A

Triploid (3N)

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8
Q

Causes of polyploidy

A
  • 2/3 are because of fertilization of an oocyte by 2 sperms
  • Other cases are because of a diploid gamete
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9
Q

Polyploidy is responsible for ?% of spontaneous abortions

A

17

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10
Q
  • Either the sperm or the egg has two full sets of chromosomes, leading to a triploid baby
  • Total chromosomes: 69
A

Triploid Syndrome

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11
Q
  • Cells have a missing single chromosome or having an extra chromosome
  • Literally translates as “not good set”
  • Most are spontaneously aborted
  • Those that survive have specific syndromes depending on which chromosomes are missing or extra
A

Aneuploidy

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12
Q

causes of aneuploidy

A
  1. Nondisjunction
  2. Anaphase lag
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13
Q
  • Meiotic error where chromosome pair does not separate at anaphase of either the 1st or the 2nd meiotic division
  • This unequal division produces a sperm or oocyte that has two copies of a particular chromosome, or none, rather than one copy
A

Nondisjunction

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14
Q
  • Result of a delayed movement (lagging) during anaphase
  • Chromosome in meiosis or a chromatid in mitosis that fails to migrate or connect to the pole of the spindle apparatus will be lost from the nucleus as division is completed
A

Anaphase Lag

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15
Q

missing chromosome

A

Hypoploidy

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16
Q

extra chromosome

A

Hyperploidy

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17
Q
  • absence of one member of a pair of chromosomes
  • 2n-1
A

Monosomy

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18
Q
  • the loss of both pairs of homologous chromosomes
  • 2n-2
A

Nullisomy

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19
Q
  • chromosomal condition characterised by an additional
    chromosome
  • 2n+1
A

Trisomy

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20
Q
  • is a condition where there is more than one copy of the chromosome relative to the normal
  • > 2n+1
A

Polysomy

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21
Q
  • Most common autosomal aneuploid among liveborns
  • Patients survive because Ch21 has the fewest genes
  • Intelligence varies but developmental milestones come
  • Common for babies born to elderly women
A

Down Syndrome or Trisomy 21
47, XY, +21

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22
Q
  • Triple copies of chromosome 18
  • Arise from nondisjunction in meiosis II
  • Most patients have great physical and intellectual disability
  • Skills remain stuck at 6 months level
  • 90% of patients die within the first month
A

Edward’s Syndrome or Trisomy 18
47, XY, +18

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23
Q
  • Kidney malformation
  • Structural heart disease
  • Omphalocele
  • Esophageal atresia
  • Cognitive delay
  • Oddly clenched fist
  • Rocker bottom foot
A

Characteristics of Edward’s Syndrome

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24
Q
  • Triple copies of chromosome 13
  • Not compatible with life
  • Serious intellectual disability
  • Great physical disability
  • Most striking feature is the fusion of the developing eyes into one large eye-like structure in the center of the face
A

Patau Syndrome or Trisomy 13
47, XY, +13

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25
Q
  • The most common trisomy in first-trimester losses.
  • The diagnosis of a trisomy 16 conceptus will most likely result in a fetal loss in the first trimester.
  • If mosaic trisomy 16 is present, the fetus may survive with near-normal developmental outcomes depending on the presence and degree of malformations.
A

Trisomy 16

26
Q
  • People with sex chromosome aneuploidy have extra or missing sex chromosomes.
  • Some conditions can result from nondisjunction in meiosis in the male or female.
  • Sex chromosome aneuploids are generally associated with much less severe symptoms and characteristics than autosomal aneuploids
A

Sex Chromosomes Aneuploidy

27
Q
  • Tall stature
  • Delayed development of speech and language skills
  • Hypotonia
  • Curved pinky fingers (clinodactyly)
  • Behavior and mental health problems
  • Premature ovarian failure or ovary abnormalities
  • Constipation or abdominal pains
A

Triple X Syndrome

28
Q
  • Monosomy of the X chromosome
  • Generally, a sporadic event and the paternal sex chromosome is the most likely one missing
  • X lang ang chromosome niya
  • Features:
    – Short stature
    – Webbing at back of neck
    – Incomplete sexual development (infertile)
    – Impaired hearing
A

Turner (XO) Syndrome

29
Q

treatment for Turner Syndrome

A

estrogen hormone therapy

30
Q
  • Karyotype: 47, XXY
  • Estimated to affect 1:500 males
  • The most common genetic or chromosomal cause of male infertility.
  • Maybe identified as an incidental finding or may present with behavioral difficulties or as infertility in an adult.
  • Technically a male with feminine features
A

Klinefelter’s (XXY) Syndrome

31
Q

Features include:
– Incomplete sexual development
– Rudimentary testes and prostate
– Long limbs, large hands and feet
– Some breast tissue development

A

Klinefelter’s (XXY) Syndrome

32
Q

treatment for Klinefelter

A

Testosterone therapy

33
Q
  • occur due to:
    – It may have too much or too little genetic material
    – It may have a stretch of DNA that is inverted or moved and inserted into a different type of chromosome
A

Structural Abnormalities

34
Q

Structurally abnormal chromosomes can be:

A
  1. Balanced
  2. Unbalanced
35
Q

– if they have the normal amount of genetic material
– Not usually any clinical significance for the patient, unless genes are disrupted, but may have consequence for offspring.

A

Balanced Structural Abnormality

36
Q

– if they have extra or missing DNA sequences
– Due to gain or loss of normal complement of genetic material

A

Unbalanced Structural Abnormality

37
Q

In some cells, the chromosome can break:

A

– Triggered by damage to DNA (radiation or chemicals)
– Part of recombination

38
Q

If breaks occur at G1 Phase

A

if not repaired at S phase, affect both chromatids

39
Q

If breaks occur at G2 Phase

A

affecting only one of the 2 sister chromatids

40
Q

Recognize and repair broken chromosomes ends

A

Enzymes

41
Q

Prevent cells with unrepaired chromosome breaks from entering mitosis

A

Cell Cycle Checkpoint Mechanism

42
Q
  • Occurs when a portion of the chromosome has broken off turned upside down and reattached
  • The genetic material is inverted
  • No loss or gain of chromosomal material thus carriers are normal
A

Inversion

43
Q
  • If the inverted segment is on the long or short arm and does not involve the centromere
  • Inversion is on one side
A

Paracentric Inversion

44
Q
  • Breaks occur in both the short and long arms and the inverted segment contains the centromere
  • Even the position of the centromere is moved
A

Pericentric Inversion

45
Q
  • An extra chromosomal segment within the same homologous chromosome or another nonhomologous chromosome
  • CROSS OVER between misaligned chromosomes
  • Chromosomal imbalance due to parental translocation or inversion
  • Often not inherited; rather they arise de novo
  • Effect on the phenotype is generally dependent on their size
A

Duplication

46
Q
  • May be caused by duplication of the gene encoding Peripheral Myelin Protein 22 (PMP 22) on chromosome 17
  • Overexpression of PMP 22
  • Manifestations:
    – High foot arches
    – Weakness of leg muscles
    – Decrease sensation of legs
A

Charcot-Marie-Tooth Disease Type 1A

47
Q
  • Refers to the loss of a segment of a chromosome
  • Often not inherited; rather they arise de novo
  • Larger deletions increase the likelihood that there will be an associated phenotype
  • Chromosomal breakage and loss of fragments can either be terminal or interstitial
  • Unequal crossing over between misaligned homologous chromosomes or sister chromatids
A

Deletion

48
Q
  • Deletion 5p- (p arm of the 5th chromosome)
  • Cry of cat syndrome
A

Cri-Du-Chat Syndrome

49
Q

minute deletion of chromosome

A

microdeletions

50
Q

the end part of the chromosome gets deleted

A

terminal

51
Q

the center part of the chromosome gets deleted

A

interstitial

52
Q
  • Rare, formed when the 2 arms have fused together to form a ring
  • More likely to be caused by the deletion of genes in the telomere regions of affected chromosome and the sticky chromosome ends fuse
  • Genes can be lost or disrupted causing symptoms
A

Ring

53
Q

Associated with mental retardation, dysmorphic facial features

A

Ring Chr 14 & Ring Chr 13

54
Q

Associated with mental retardation, dwarfism & microcephaly

A

Ring Chr 15

55
Q

– Associated with epilepsy

A

Ring Chr 20 Syndrome

56
Q

Ring X Chromosome

A

Causes Turner Syndrome

57
Q
  • Is a structural rearrangement involving 2 non-homologous chromosomes
  • Two nonhomologous chromosomes exchange segments
  • Eg. Chromosome 1 & Chromosome 4
A

Translocation

58
Q
  • When segments from 2 different chromosomes have been exchanged
  • If translocation breakpoint interrupts a gene, there may be an associated phenotype
A

Reciprocal Translocation

59
Q
  • A particular type of translocation
  • Involves reciprocal transfer of the long arms of 2 of the Acrocentric Chromosome 13,14,15,21 or 22
  • Acrocentric chromosomes break at the centromere and their long arms fuse
  • Eg. Between Chromosome 14 & 21
A

Robertsonian Translocation

60
Q
  • Rare condition where chromosomes have identical short and long arms
  • Formed when centromeres divide along the incorrect plane during meiosis
  • These are formed when a chromosome has lost one of its arms and this arm is replaced with an exact copy of a chromosome segment including the centromere
  • Seen in Turner Syndrome & tumor cells
A

Isochromosome

CYTOGENETICS (11 decks)

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