Lecture 15 Chromosome abnormalities Flashcards

1
Q

Define Anueploidy

A

This is the loss of gain of a single chromosome.

- Examples include monosomy, trisomy,

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2
Q

What is meant by aneuploidy

A

Type of chromosomal abnormality where the number of chromosomes is abnormal but not loss or gain of a complete set of chromosomes.

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3
Q

Explain the two main causes of Aneuploidy in humans (be specific)

A

1) Non disjunction of homologous chromosomes in Meiosis I

2) Non disjunction of sister chromatids in meiosis II.

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4
Q

Downs syndrome is which type of aneuploidy

A

Trisomy 21. Involves an extra copy of chromosome 21. 2n +1.

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5
Q

State the cause of 95 percent of downs syndrome cases

A

Non disjunction of homologous chromosomes in meiosis I or non disjunction of sister chromatids in meiosis II.

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6
Q

State the cause of 5 percent of down syndrom cases. Explain what it is.

A
  • Robertsonian translocation accounts for 5% of all DS cases.
  • ## Robertsonian translocation involves both chromosome 21 and 14.
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7
Q

State the type of Aneuploidy involded in turners syndrome

A

Monosomy ( 2n-1).

Turners syndrome results due to the loss of an X chromosome

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8
Q

State the karyotype for Turners syndrome

A

45 XO

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9
Q

Turners syndrome only affects which sex

A

Females

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10
Q

How many barr bodies will be visible in those affected by turners syndrome

A

No barr bodies visible because only one X chromosome undergoes inactivation!

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11
Q

State the karyotype of those affected by Klinefelters syndrome

A

47 XXY

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12
Q

Klinefelters syndrome affects which sex only

A

Males

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13
Q

How many barr bodies will be visible in klinefelters syndrome patients ( per cell)

A

1

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14
Q

Define and explain the pseudoautosomal region

A
  • pseudoautosomal region is a conserved, homologous DNA sequences that exist on the X and Y chromosome.
  • Genes in the PAR region are inherited just like any autosomal genes.
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15
Q

What is the function of the pseudoautosomal region

A

Crossing over between the X and Y chromosomes is restricted to the PAR regions.
The function of the PAR regions is that they allow X and Y chromosomes to pair and properly segregate during meiosis in males.

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16
Q

Explain the process of X chromosome inactivation

A

Females have 2 X chromsomes.
Thus, as a form of dosage compensation, ONE of the X chromsomes is inactivated. This inactivated chromosome is cytologically visible as a barr body.

17
Q

How many X chromosmes undergo inactivation per cell in a female?

A

Per cell, just one X chromosome is inactivated, showing up as one X chromosome per barr body.

18
Q

What happens to the pseudoautosomal genes during X inactivation

A

The PAR regions escape X inactivation.

19
Q

What happens to human oocytes?

A

Human oocytes are paused in meiosis I for decades.

20
Q

When are human oocytes produced?

A

Before birth in a female

21
Q

What is a major cause of aneuploidy in older women

A

Premature loss of cohesion protein complex which holds the two homologues together up until anaphase causes formation of 2 univalents.

22
Q

How many protein encoding genes are found in the mitochondrial genome. Are the genes within the mitochondrial genome smaller or larger than normal mitochondrial regions?

A
  • Theres 13 protein encoding genes in the mitochondrial genome.
  • Genes of the mt genome are usually smaller.
  • Many of the genes code for proteins involved in oxidative phosphorylation.
23
Q

Explain how the mitochondrial genome is inherited?

A

Maternal inheritance of extra nuclear mitochondria

24
Q

Describe the transmission of extranuclear genomes (mitochondria and chloroplast)

A

Often transmitted from one generation to the next in a uniparental pattern - maternal inheritance

25
State the most common mode of transmission of extranuclear genomes in plants and algae
Uniparental maternal inheritance.
26
Explain mitochondrial DNA disease/s
Genetic disorder that occurs when the mitochondria of the cell fail to produce enough energy for the cell or organ to function. - Many forms of mitochondrial disease, and can arise from defe
27
Defects which cause mitochondrial disease can be from which type of DNA
Mutations in either the mitochondrial dna iteslf or the cells nuclear DNA.
28
How many barr bodies does a patient with Turners syndrome typically have?
No barr bodies because at least one X chromosome is required for embryonic development, so you cannot have both X chromosomes being inactivated or you wouldn't exist/survive.
29
State the mode of inheritance in pseudoautosomal genes
Pseudoautosomal genes exhibit autosomal patterns of inheritance, rather than a sex linked pattern of inheritance.
30
An XX female has how may barr bodies per cell
One barr body
31
An XXX female has how many barr bodies per cell
2 barr bodies per cell
32
An XXY klineflter male has how many barr bodies per cell
1 barr body per cell. as one is needed/
33
Which phase are primary oocytes paused in before birth
Before birth primary oocytes are arrested in prophase I, with paired replicated chromosomes.
34
Explain why premature loss of cohesion gives rise to aneuploid (n+1) gametes eg instead of n=23, n=24.
dont knowwwww
35
Name some examples of molecules endoded for by the mitochondrial genome
cytochrome oxidase, NADH dehydrogenase, and ATPase.