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Maternal > Embryo pt.3 > Flashcards

Embryo pt.3 Flashcards

1
Q

How common are meiotic errors in humans?

A
  • Very common in humans
  • The incidence of chromosomal abnormalities is approximately 0.6% in newborns, 6% in stillbirths and 60% in spontaneous abortions
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2
Q

What can meiotic chromosomal abnormalities be divided into?

A

Aneuploidy (i.e. numeric) and chromosomal rearrangements (i.e. structural)

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3
Q

Which trisomies are compatible with life?

A
  • Only trisomies 13, 18, and 21
  • Other ones lead to miscarriage
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4
Q

What is the cause of chromosomal abnormalities? What do they cause?

A
  • Most of these errors are generated during meiosis particularly in oogenesis rather than spermatogenesis
  • Abnormal development; mental, physical, infertility, behavioral and impaired sexual development
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5
Q

How many gametes are produced during gametogenesis?

A
  • Four in spermatogenesis
  • One in oogenesis
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6
Q

Describe initiation of meiosis in female vs male gametogenesis?

A
  • Female: Once in a finite population of cells
  • Males: Continuously in mitotically dividing stem cell populations
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7
Q

/

A

/

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8
Q

What are possible chromosome structural rearrangements that can occur?

A

Duplication and/or deletion of a chromosome portion,microdeletions and microduplications, inversions and translocations

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9
Q

What happens in chromosomal inversions?

A
  • In inversion a piece of a chromosome is detached, 180° rotated and eventually reinserted in the chromosome (i.e.segment of chromosome is reversed)
  • In this case the problem will be encountered at the level of nucleotide sequence
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10
Q

What is nondisjunction?

A
  • A pathological process in which homologous chromosomes fail to separate during anaphase of either meiosis or mitosis
  • This leads to an abnormal number of chromosomes in the gamete
  • This kind of mechanism will affect both daughter cells (if it occurs in meiosis 1), one having an extra copy of a chromosome and the other lacking one
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11
Q

What can the causes of birth defects be divided into?

A

Three broad categories:
- Genetic factors, such as chromosomal abnormalities
- Environmental factors, such as drugs and viruses
- Multifactorial inheritance (genetic and environmental factors acting together)
50% to 60% of birth defects have no known cause

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12
Q

What is an abnormal number of chromosomes called?

A

Aneuploidy

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13
Q

What has aneuploidy been linked to aside from gametogenesis related pathologies?

A
  • Aneuploidy can shift a cell’s balance to a pro-tumorigenic state, and it is considered a hallmark in many cancers.
  • Aneuploidy is generally disadvantageous for cells and there is ample evidence of the negative effect of aneuploidy on the fitness of nonmalignant cells
  • Aneuploidy should not be considered as exclusively linked to gametogenesis related pathologies
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14
Q

What forms does aneuploidy come in?

A
  • Aneuploid: Monosomy, nullisomy, trisomy, tetrasomy, pentasomy
  • Polyploid: Triploid and tetraploid fetus
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15
Q

What is aneuploidy?

A

Any deviation from the diploid number of 46 chromosomes

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16
Q

How common are aneuploidies?

A

Occurs in 3-4% of clinically recognized pregnancies

17
Q

How many chromosomes does a triploid fetus have?

A

69 chromosomes

18
Q

What is the difference between aneuploid and polyploid?

A
  • Aneuploid is an individual who has a chromosome number that is not an exact multiple of the haploid number 23 (e.g. 45, 47)
  • Polyploid is an individual who has a chromosome number that is an exact multiple of the haploid (e.g. 69)
19
Q

What are mechanisms causing aneuploidy?

A

They include nondisjunction and anaphase lag

20
Q

What is an anaphase lag?

A
  • Delayed movement of a chromosome or chromatid during anaphase resulting in the loss of the genetic material from inclusion into either daughter nucleus
  • Basically, a chromosome moves so slowly that it doesn’t get incorporated into the nucleus of the daughter cells.
21
Q

What is aneuploidy’s cause associated to?

A
  • Aneuploidy is associated mainly to errors happening during oogenesis
  • Maternal age is the most significant factor in the etiology of aneuploidy
  • We think that this association is due to the increasing time of meiosis arrest in the primary follicles
22
Q

Describe aneuploidy in spermatogenesis

A
  • Not much information
  • In normal control donors we could find 1-2% of aneuploid spermatozoa
  • In sperm cells it is more common to find structural abnormalities than numerical ones
  • Paternal age effect on aneuploidy is less
    understood. This lack of association between age and aneuploidy is related to the particular characteristics of male gametogenesis, which is a process that could last for entire life differently from oogenesis
23
Q

What are common forms of aneuploidy?

A

Trisomy of autosomes:
- Trisomy 21
- Trisomy 18
- Trisomy 13
Trisomy of sex chromosomes:
- 47, XXY
- 47 XYY
- 47 XXX
Monosomy of sex chromosome
- 45,X, or 45,X0 (X chromosome missing or partially missing)

24
Q

What is the most common cause of chromosomal structural rearrangements?

A

Most commonly result from chromosome breakage, followed by reassembly in an abnormal combination

25
Q

What are examples of chromosome structural rearrangement pathologies?

A
  • Cri-du-chat syndrome
  • Wolf- Hirshon syndrome (WHS)
26
Q

What causes cri-du chat syndrome

A

Deletion in 5p (short arm of chromosome 5)

27
Q

What causes Wolf- Hirschhorn syndrome (WHS)?

A

Deletion of 4p (short arm of chromosome 4)

28
Q

What is cri-du-chat syndrome characterized by?

A

High-pitched cat-like cry, but there are also other features such as microcephaly, severe cognitive deficiency, hypertelorism, problems in skeletal muscles development, congenital heart disease, and hypotonia (to the point that they cannot stand up alone).

29
Q

What is hypertelorism?

A

Increased distance between orbits

30
Q

What is Wolf-Hirschhorn syndrome (WHS) characterized by?

A

Skeletal abnormalities and intrauterine growth retardation are the main features of this syndrome

31
Q

What is trisomy 21 known as?

A

Down syndrome

32
Q

What is trisomy 18 known as?

A

Edward’s syndrome

33
Q

What is trisomy 13 known as?

A

Patau syndrome

34
Q

What is 47, XXY also known as?

A

Klinefelter syndrome

35
Q

What is 47, XYY also known as?

A

Jacobs syndrome

36
Q

What is 47 XXX also known as?

A

Triple X syndrome

37
Q

What is 45,X, or 45,X0 also known as?

A

Turner syndrome

38
Q

What is the incidence rate of trisomy in women?

A

In women under the age of 25, about 2% of clinically recognized pregnancy are trisomic, whereas in women over 40 the frequency is
approximately 35%

Maternal (9 decks)

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