Section IIE Flashcards

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1
Q

How is X inactivation random, fixed and imcomplete?

A
  • Random: Each cell chooses which X chromosome to inactivate so different cells my choos a maternal or paternal X
  • Fixed: Once the X is inactivated it is not longer activated unless in gamete production in females
  • Incomplete: X chromosome is not completely inactivated which explains the disease phenotype in people with abnormal numbers of sex chromosomes
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2
Q

What are the characteristics and examples of an X-linked recessive trait?

A
  • Mostly males are affected (common to see a female affected followed by all males)
  • absence of father-to-son transmission.
  • Hemophilia A, DMD, red-green color blindness
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3
Q

What are the characteristic of an X linked dominant disease?

A
  • KEY: Affected fathers will transmit to ALL of their daughters.
  • becuase one X from each parent and father only has one X to give.
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4
Q

What is the purpose of the XIST gene?

A

-encodes an RNA transcript that coats the Barr body (inactivated X chromosome)

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5
Q

What is the purpose of GC methylation in barr bodies?

A

-GC dinucleotide methylation serves to maintain inactivation of the X chromosome

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6
Q

What are the father-to-son transmission patterns in X-linked and Y-linked diseases?

A

X-linked: No father to son transmission

Y-linked: always father to sone transmission

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7
Q

What gene is defective in hemophilia A and what are the symptoms?

A
  • Gene for Factor VIII
  • Bleeding (bruising, hemorrhaging, into joints, all kinds of bleeding)
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8
Q

What is the differnece in mutation between a mild and severe hemophilia?

A
  • mild generally results from a missense mutation
  • severe generally results from a nonsense or frameshift mutation
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9
Q

What gene is dysfunctional in DMD?

A

-The DMD gene which encodes Dystrophin

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10
Q

What is the significant of dystrophin?

A
  • Dystrophin (encoded by the DMD gene) is an important structural protein of muscle cells.
  • when it is dificient or absent, muscle cells are unable to maintain their integrity and lyse
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11
Q

What is the significant of CK in people with DMD?

A

-Creatine Kinse levels are elevated (up to 20x) due to the instability of muscle cells.

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12
Q

What is the inability to precieve green?

A

deuteranopia

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13
Q

What is the inability to precieve red?

A

-protanopia

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14
Q

What is the causitive factor in color blindness?

A

-unequal crossover of the red and green genes

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15
Q

What are three X-linked dominant disorders?

A
  • hypophophatemic rickets: kidneys can’t reabsorb phosphate–> abnormal ossification
  • incontinentia pigmenti: abnormal skin pigmentation that FOLLOWS DERMATOMES–>only females are born
  • Rett Syndrome: autism, ataxia, mental retardation
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16
Q

What is unusual about the inheritance pattern of fragile X syndrome?

A

-Daughter of normal transmitting males were never affected bu the sons of those daughters were affected.

17
Q

How do expansion repeats explain the sherman paradox in fragile X?

A

-expansion repeats occur in femails so the carry males pass down the mutation and the females then amplify the repeat.

18
Q

What gene is defective in fragile X? What are its ranges of mutation?

A
  • FMR1 gene (has a normal CGG repeat for 6-50 bp)
  • 50-200 repeats in normal transmitting males and their daughters
  • >200 in fragile X (called a full mutation)
19
Q

Does mitochondrial DNA have introns?

A

-no

20
Q

What is heteroplasmy in reference to mtDNA?

A

-explain that a single cell can harbor some molecules that have a mtDNA mutation an others that do not.

21
Q

What are the characteristic of LHON (mutation, heteroplasmy, symptoms)?

A
  • Leber Hereditary Optic Neuropathy
  • characterized by loss of the central visual field in the third decade of life
  • missense mutation in mtDNA with little heteroplasmy
22
Q

What are the characteristics of MERRF syndrome (mutation, heteroplasmy, symptoms)?

A
  • myoclonic epilepsy with ragged-red fiber syndrome
  • single base mutation in a tRNA gene
  • heteroplasmic and highly variable
  • epilepsy, dementia, ataxia, myopathy
23
Q

What is MELAS?

A

-mitochondrial enchephalomyopathy and storke-like symptoms

24
Q

What is similar between MELAS and MERRF?

A

-both highly heteroplasmic and variable

25
Q

What mutation is involved in MELAS?

A

-Single base tRNA mutation

26
Q

What disease results from a deletion on the paternal side of chromosome 15 (when the maternal 15 is imprinted)?

A

-Prader-Willi syndrome/

27
Q

What ensues from deletion on the maternal chromosome 15 when the paternal 15 is imprinted?

A

Angelman syndrome.