Chromosome Abnormalities Flashcards

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1
Q

Numerical Abnormalities

A

Missing or having extra chromosomes (wrong # chromosomes)

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2
Q

Structural Abnormalities

A

Chromosome is altered by deletion, duplication, breakage (problems WITHIN a chromosome)

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3
Q

Aneuploidy

A

The gain or loss of a whole chromosome

(Most common chromosome abnormality in humans)

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4
Q

Aneuploidy is the leading genetic cause of…

A

spontaneous miscarriage and congenital birth defects

(also seen in most tumors)

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5
Q

Most common cause of aneuploidy…

A

Nondisjunction

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6
Q

Non-Disjunction

A

The failure of homologs or sister chromatids to separate during cell division

(= “not coming apart”)

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7
Q

Non-Disjunction can occur at: (3)

A

Meiosis I –> Anaphase I (homologs don’t separate)

Meiosis II –> Anaphase II (sister chromatids don’t separate)

Mitosis –> Anaphase (sister chromatids don’t separate)

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8
Q

Non-Disjunction in Meiosis I (results)

A

2 gametes = (n + 1) = Extra chromosome
2 gametes = (n - 1) = Lost chromosome

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9
Q

Non-Disjunction in Meiosis II (results)

A

1 gamete = (n + 1) = Extra chromosome
1 gamete = (n -1) = Lost chromosome
2 gametes = (n) = Normal

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10
Q

Monosomic Zygote

A

(2n-1) = Lost chromosome

Normal gamete + (n - 1) gamete

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11
Q

Trisomic Zygote

A

(2n + 1) = Gained Chromosome

Normal gamete + (n + 1) gamete

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12
Q

What does aneuploidy affect?

A

1) Gene dosage
2) Recessive “unmasking”
3) Sterility

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13
Q

Gene Dosage

A

The # of copies of a gene that are actively being expressed

–> Proportionally reflects the RNA and protein products in a cell

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14
Q

Affects of aneuploidy on gene dosage

A

A missing or extra chromosome throws off the overall gene balance in the chromosome set (dosage)

–> Can lead to more or less RNA/Protein products

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15
Q

Recessive “unmasking” (due to aneuploidy)

A

A missing chromosome = 1 allele determines the phenotype for those now missing genes

–> Allows any harmful recessive alleles on the single chromosome to be phenotypically expressed (hemizygous)

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16
Q

Hemizygous

A

Having only one allele of a gene

17
Q

Sterility (due to aneuploidy)

A

One extra/missing chromosome interferes with the pairing of homologs during meiosis I (odd # can’t all pair)

== Halt of the cell cycle at M checkpoint

–> Meiosis can’t be completed = no gametes = sterility

18
Q

Non-Disjunction in Mitosis

A

May have a phenotypic effect depending on WHEN non-disjunction occurs:

Early in Development = Aneuploidy will be passed on to a large # of daughter cells = major phenotypic effect

Late in Development = Aneuploidy only passed onto those daughter cells (less) = possible large effect (depends)
—> Tumor cells commonly have aneuploidy

19
Q

Cause of Non-Disjunction (5)

A

Really any defects in cell division machinery:

1) Defects in kinetochore-MT attachment to chromosome
2) Defects in kinetochore complex assembly
3) Weakened meiotic/mitotic checkpoint
4) Defects in spindle pole function and/or #
5) Completely inactive checkpoints (could cause non-disjunc. of multiple or all chromosomes)

20
Q

Aneuploidy frequency in humans is _________________ BUT it usually results in _____________________

A

1) quite high (>10% of all pregnancies)

2) embryonic death

21
Q

Only certain aneuploidies can be tolerated through to adulthood, including…

A

Chromosomes X, Y, 21

22
Q

Down Syndrome

A

AKA Trisomy 21

–> An extra chromosome 21 (3 copies instead of 2)

–> Leads to extensive neuronal, intellectual, skeletal, developmental delats

23
Q

Chromosome 21

A

Smallest human chromosome (<1.5% of DNA)

–> Probably why people with abnormality on this chromosome can survive (has less of an impact than other chromosomes)

24
Q

Down Syndrome cases strongly correlate to…

A

Mother’s Age

–> The older the mother, the more common Down Syndrome offspring become

25
Q

Down Syndrome may be linked to…

A

Age dependent abnormality in the M (spindle) checkpoint during meiosis I that is leading to non-disjunction

26
Q

Fetal Genetic Testing

A

There are screening and then diagnostic tests that can be run

27
Q

Screening Tests

A

Imaging / Blood tests (non-invasive)

28
Q

Diagnostic Tests (2)

A

1) Amniocentesis
2) Chorionic Villus Sampling (CVS)

29
Q

Amniocentesis

A

Needle inserted into uterus to get amniotic fluid sample which contains fetal cells

–> Sample is then sent to undergo biochemical testing and/or karyotyping

–> Higher risk + can be done later

30
Q

Chorionic Villus Sampling (CVS)

A

Narrow suctioned tube inserted into the cervix and through to the uterus to get a small sample of the placenta

–> cells of the chorionic villi are derived from the fetus

–> The sample can then undergo biochemical testing and/or karyotyping

–> Lower risk + can be done earlier