Section IIE Flashcards
How is X inactivation random, fixed and imcomplete?
- 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
What are the characteristics and examples of an X-linked recessive trait?
- 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
What are the characteristic of an X linked dominant disease?
- KEY: Affected fathers will transmit to ALL of their daughters.
- becuase one X from each parent and father only has one X to give.
What is the purpose of the XIST gene?
-encodes an RNA transcript that coats the Barr body (inactivated X chromosome)
What is the purpose of GC methylation in barr bodies?
-GC dinucleotide methylation serves to maintain inactivation of the X chromosome
What are the father-to-son transmission patterns in X-linked and Y-linked diseases?
X-linked: No father to son transmission
Y-linked: always father to sone transmission
What gene is defective in hemophilia A and what are the symptoms?
- Gene for Factor VIII
- Bleeding (bruising, hemorrhaging, into joints, all kinds of bleeding)
What is the differnece in mutation between a mild and severe hemophilia?
- mild generally results from a missense mutation
- severe generally results from a nonsense or frameshift mutation
What gene is dysfunctional in DMD?
-The DMD gene which encodes Dystrophin
What is the significant of dystrophin?
- 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
What is the significant of CK in people with DMD?
-Creatine Kinse levels are elevated (up to 20x) due to the instability of muscle cells.
What is the inability to precieve green?
deuteranopia
What is the inability to precieve red?
-protanopia
What is the causitive factor in color blindness?
-unequal crossover of the red and green genes
What are three X-linked dominant disorders?
- 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