CHROMOSOME ABNORMALITIES Flashcards
1
Q
typical number of chromosomes in a human cell
A
46: 23 pairs
2
Q
Types of Chromosomal Abnormalities
A
- Constitutional Abnormalities
- Acquired or Somatic Abnormalities
- Numerical Anomalies
- Structural Anomalies
3
Q
Refers to anomalies that are inborn and have been always present in the embryo
A
Constitutional Abnormalities
4
Q
Developed due to exposures, habits, or malignancies
A
Acquired or Somatic Abnormalities
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
6
Q
- Presence of extra sets of chromosomes
A
Polyploidy
7
Q
an individual who has 3 sets or copies of chromosomes
A
Triploid (3N)
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
9
Q
Polyploidy is responsible for ?% of spontaneous abortions
A
17
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
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
12
Q
causes of aneuploidy
A
- Nondisjunction
- Anaphase lag
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
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
15
Q
missing chromosome
A
Hypoploidy
16
Q
extra chromosome
A
Hyperploidy
17
Q
- absence of one member of a pair of chromosomes
- 2n-1
A
Monosomy
18
Q
- the loss of both pairs of homologous chromosomes
- 2n-2
A
Nullisomy
19
Q
- chromosomal condition characterised by an additional
chromosome - 2n+1
A
Trisomy
20
Q
- is a condition where there is more than one copy of the chromosome relative to the normal
- > 2n+1
A
Polysomy
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
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
23
Q
- Kidney malformation
- Structural heart disease
- Omphalocele
- Esophageal atresia
- Cognitive delay
- Oddly clenched fist
- Rocker bottom foot
A
Characteristics of Edward’s Syndrome
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
25
* 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.
Trisomy 16
26
* 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
Sex Chromosomes Aneuploidy
27
* **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
Triple X Syndrome
28
* 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
Turner (XO) Syndrome
29
treatment for Turner Syndrome
estrogen hormone therapy
30
* 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**
Klinefelter’s (XXY) Syndrome
31
Features include:
– Incomplete sexual development
– Rudimentary testes and prostate
– Long limbs, large hands and feet
– Some breast tissue development
Klinefelter’s (XXY) Syndrome
32
treatment for Klinefelter
Testosterone therapy
33
* 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
Structural Abnormalities
34
Structurally abnormal chromosomes can be:
1. Balanced
2. Unbalanced
35
– 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.
Balanced Structural Abnormality
36
– if they have extra or missing DNA sequences
– Due to gain or loss of normal complement of genetic material
Unbalanced Structural Abnormality
37
In some cells, the chromosome can break:
– Triggered by damage to DNA (radiation or chemicals)
– Part of recombination
38
If breaks occur at G1 Phase
if not repaired at S phase, affect both chromatids
39
If breaks occur at G2 Phase
affecting only one of the 2 sister chromatids
40
Recognize and repair broken chromosomes ends
Enzymes
41
Prevent cells with unrepaired chromosome breaks from entering mitosis
Cell Cycle Checkpoint Mechanism
42
* 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
Inversion
43
* If the inverted segment is on the long or short arm and does not involve the centromere
* Inversion is on one side
Paracentric Inversion
44
* Breaks occur in both the short and long arms and the inverted segment contains the centromere
* Even the position of the centromere is moved
Pericentric Inversion
45
* 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
Duplication
46
* 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
Charcot-Marie-Tooth Disease Type 1A
47
* 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
Deletion
48
* Deletion 5p- (p arm of the 5th chromosome)
* Cry of cat syndrome
Cri-Du-Chat Syndrome
49
minute deletion of chromosome
microdeletions
50
the end part of the chromosome gets deleted
terminal
51
the center part of the chromosome gets deleted
interstitial
52
* 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
Ring
53
Associated with mental retardation, dysmorphic facial features
Ring Chr 14 & Ring Chr 13
54
Associated with mental retardation, dwarfism & microcephaly
Ring Chr 15
55
– Associated with epilepsy
Ring Chr 20 Syndrome
56
Ring X Chromosome
Causes Turner Syndrome
57
* Is a structural rearrangement involving 2 non-homologous chromosomes
* Two nonhomologous chromosomes exchange segments
* Eg. Chromosome 1 & Chromosome 4
Translocation
58
* When segments from 2 different chromosomes have been exchanged
* If translocation breakpoint interrupts a gene, there may be an associated phenotype
Reciprocal Translocation
59
* 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
Robertsonian Translocation
60
* 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
Isochromosome
