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M2M Week3 > Numerical and Structural Chromosomal Abnormalities > Flashcards

Numerical and Structural Chromosomal Abnormalities Flashcards

1
Q

Describe mitosis (as compared to meiosis)

A

One round of chromosome segregation; daughter cells identical in chromosomal content to the parental cell. DNA replication precedes each round of chromosome segregation. No pairing of homologous chromosomes. Infrequent recombination. Centromeres on paired sister chromatids segregate at each anaphase. Occurs in somatic cells and in germ line precursor cells prior to entry into meiosis

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2
Q

Describe meiosis (as compared to mitosis)

A

Two rounds of chromosome segregation without an intervening round of DNA replication. Parental cells must be diploid and the chromosome number is halved in the resultant cells. Requires the pairing of homologous chromosomes and recombination. Centromeres on paired sister chromatids divide only at anaphase II. Occurs only in the germ line

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3
Q

Name 3 categories of human chromosomes (based on cetromere)

A

Metacentric (centromere in middle; two arms are equal length). Submetacentric (centromere not quite in middle). Acrocentric (centromere near one end)

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4
Q

Euploidy

A

“Good ploidy:” full set of chromosomes - 46

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5
Q

Polyploidy

A

“Many ploidy:” Triploid - 69. Tetraploid - 92

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6
Q

Aneuploidy

A

“Not good ploidy.” Trisomy - 47. Monosomy - 45

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7
Q

Autosomal monosomies vs. monosomatic at X chromosome

A

Autosomal monosomies do not survive. BUT 45 X can survive (Turner syndrome)

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8
Q

Where do most errors occur that lead to trisomies?

A

Generally; maternal errors in 1st meiotic division

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9
Q

What are the effects on gametes if nondisjunction occurs in meiosis I?

A

All gametes are abnormal. Either 2n or 0n.

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10
Q

What are the effects on gametes if nondisjunction occurs in meiosis II?

A

Half of gametes are abnormal. 2 gametes will be normal (n); 1 will be 2n; 1 will be 0n

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11
Q

Describe relationship between crossing-over and nondisjunction

A

Crossover events that occur too near or too far from the centromere increase chromosome nondisjunction. Centromere-distal appears to lead to errors in meiosis I; proximal appears to lead to errors in MII. Nondisjunction events are also related to the frequency of crossover events (reduction of recombination events increases likelihood of nondisjunction).

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12
Q

What kind of aneuploidies are tolerated at birth?

A

Trisomy 13; 18; 21. Sex chromosome aneuploidy

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13
Q

Describe Down syndrome

A

47; XY (or XX); +21. Trisomy 21. Characteristic facies; short stature; hypotonia; moderate intellectual disabilities; cardiac anomalies; leukemia in infancy.

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14
Q

Describe Edwards syndrome.

A

47; XY (or XX); +18. Trisomy 18. Small for gestational age; small head; clenched fingers; rocker-bottom feet.

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15
Q

Describe Patau syndrome

A

47; XY (or XX); +13. Trisomy 13. Characteristic facies; severe intellectual disabilities. Congenital malformations � holoprosencephaly; facial clefts; polydactyly; renal anomalies

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16
Q

Describe Turner syndrome

A

45; X. Short stature; webbed neck; edema of hands and feet; broad shield-like chest; narrow hips; renal and cardiovascular anomalies; gonadal dysgenesis (failure of ovarian maintenance). Many (25%) Pts have mosaicism (thought to contribute to survival).

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17
Q

Describe Klinefelter syndrome

A

47; XXY. Tall stature; hypogonadism; elevated frequency of gynecomastia; high frequency of
sterility; language impairment

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18
Q

Describe mosaicism

A

2 or more different cell karyotypes from the same individual. Most commonly caused by nondisjuction in early embryonic development.

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19
Q

Germ-line mosaicism

A

Result of mitotic nondisjunction in germ cell precursor

20
Q

Balanced vs. unbalanced structural rearrangements

A

Balanced: intrachromosomal rearrangements; no loss or gain of genetic information; usually normal phenotype. Unbalanced: loss or gain of genetic info; usually abnormal phenotype.

21
Q

What are the 3 main types of balanced rearrangements?

A

Inversions (pericentric and paracentric); reciprocal translocation; Robertsonian translocation

22
Q

General description of inversion

A

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. Pericentric and paracentric

23
Q

What is a pericentric inversion?

A

It includes the centromere

24
Q

Describe what can occur with a pericentric inversion during meiosis

A

A loop is formed. If crossing over occurs at the edges there is not an issue (both chromosomes are balanced). Baby will be healthy; 50% will be carriers of the inversion. If the crossover occurs within the loop chromosomes produced will be unbalanced; both will lose some genes and have duplicates of other genes. Baby will either be lost or if carried to term will have defects.

25
Q

Describe Rec 8 syndrome

A

Trisomy for 8q22.1 or monosomy for 8p23.1. Derived from pericentric inversion 8 carrier(inv(8)(p23.1q22.1). Founder effect - 1st described in Hispanic families in Western states.

26
Q

What is a paracentric inversion?

A

Does not include the centromere

27
Q

Describe what can occur with a paracentric inversion during meiosis

A

A loop is formed. If a crossover occurs within the loop the chromosomes produced are both very unbalanced; could be dicentric or acentric. There will be spontaneous abortion (associated with inv(11)(p13p15) and aniridia; Xp/q inversions and Turner Syndrome anomalies)

28
Q

What is a reciprocal translocation?

A

When two non-homologous chromosomes break and exchange genetic material. Carriers usually healthy but risks for offspring.

29
Q

What occurs during meiosis for reciprocal translocation?

A

Chromosomes form a quadrivalent. If ALTERNATE chromosomes pair off the resulting chromosomes will be balanced. Could be normal or a carrier. If ADJACENT pairing occurs the resulting chromosomes will be unbalanced. Depending on size of translocation; baby may be lost or there may be defects.

30
Q

Describe Robertsonian translocations

A

Fusion of two acrocentric chromosomes within their centromeric regions; resulting in the loss of both short arms (containing rDNA repeats)

31
Q

What is the most common RT?

A

13;14. Also most common translocation in humans

32
Q

Are Robertsonian translocations balanced or unbalanced? Why?

A

Usually balanced (although unbalanced do exist). They result in the reduction of chromosome number (45) but the loss of some rDNA repeats is not deleterious.

33
Q

Which chromosomes are acrocentric?

A
        1. 22
34
Q

Describe Unbalanced Robertsonian translocations. How many chromosomes; etc.

A

46 chromosomes. But because there are actually two fused chromosomes it becomes unbalanced. Ex when 21 is fused to 14 there are actually 3 copies of chromosome 21. Usually between 13/14 and 21. Will result in Down syndrome.

35
Q

Continguous gene syndromes AKA microduplications/microdeletions

A

Abnormal phenotypes caused by gain or loss of a set of neighboring genes

36
Q

Wolf-Hirschhorn syndrome

A

del(4p16.3). Facial clefting. Prominent ears. Microcephaly. Intellectual disabilities

37
Q

Beckwith-Wiedemann syndrome

A

dup(11p15.5) (paternal). Overgrowth. Omphalocele. Predisposition to Wilms and other tumors

38
Q

Cri du chat syndrome

A

del(5p15.2). Microcephaly. Characteristic cry. Seizures and intellectual disabilities

39
Q

Angelman syndrome

A

del(15q11-q13) (maternal). Seizures. Intellectual disabilities

40
Q

Williams syndrome

A

del(7q11.2). Congenital heart disease. Short stature

41
Q

Prader-Willi syndrome

A

del(15q11-q13) (paternal). Hypotonia. Hypopigmentation. Hypogenitalism. Obesity

42
Q

Langer-Giedion syndrome

A

del(8q24.1). Tricho-rhino-pharangeal syndrome. Multiple exostoses

43
Q

Miller-Dieker syndrome

A

del(17p13.3) lissencephaly (agyria). profound intellectual disabilities

44
Q

WAGR syndrome

A

del(11p13). Wilms tumor. Aniridia. genitourinary anomalies. intellectual disabilities

45
Q

DiGeorge syndrome

A

del(22q11.2). absent or hypoplastic thymus and parathyroids. congenital heart disease

46
Q

Deletion or Duplication 22q11.2 syndrome

A

Caused by disturbance of migration of neural crest cells into the pharyngeal arches/pouches -> cleft lip/palate and heart defects. T cell dysfunction (thymus). Hypocalcemia (parathyroid). Critical protein: TBX-1

M2M Week3 (5 decks)

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