Flashcards in 2E- Sex-Linked and Nontraditional Inheritance Deck (57)
What is the Lyon hypothesis?
stated that X inactivation occurs early in female embryonic development and that the X chromosome contributed by the father is inactivated in some cells, whereas in other cells the X chromosome contributed by the mother is inactivated
When and where does X inactivation occur?
takes place 7-10 days after fertilization takes place at the X-inactivation center
What is the X inactivation center?
a single 1-Mb region on the X chromosome long arm that spreads along the chromosome
Is X chromosome inactivation random or selective?
True or False: once an X chromosome is inactivated in a cell, it will remain inactive in all decedents of that cell
Is the inactivated X completely inactivated or can a small mount of genes still get transcribed?
~15% of the genome can be transcribed. This is why Turners syndrome (XO) has weird stuff
What are Barr bodies?
inactive highly condensed X chromosome found in somatic cells of normal females
What is the XIST gene?
found in the X inactivation center and is transcribed only on the inactive X chromosome
What is the role of the XIST gene products?
RNA transcript made from the XIST gene is not translated into protein it remains in the nucleus and coats the inactive X chromosome
Methylation of what dinucleotides is in the inactivated X chromosome?
How many Barr bodies does a female have?
the number of Barr Bodies in somatic cells is always one less than the number of X chromosomes
Are X-linked diseases more common among males or females?
Males. They only have 1 X chromosome
Is there father-to-son transmission in X-linked disorders?
No. Papa only gives a Y to the son
Let's say a dude has a recessive X-linked disorder. What will be the genotype of the children? (assuming the mom is a normal noncarrier)
Boys- all unaffected. XY
Girls- all carriers. XX*
Let's say a chick is a carrier for a X linked recessive disorder. What will the children's genotype look like? (assuming dad is normal)
Boys- 1/2 will be normal (XY) and 1/2 will be affected (X*Y)
Girls- 1/2 will be noncarriers (XX) and 1/2 will be carriers (X*X)
Let's say there's an affected father with an X linked disease. He fertilizes a woman who is a carrier for the same disease. What will the kids genotypes look like?
X*Y (x) X*X
Girls- 50% affected, 50% carriers
Boys- 50% affected, 50% normal
What type of disorder is hemophilia A?
X linked recessive
Which factor is missing in hemophilia A?
What types of mutations cause severe hemophilia A?
frameshift or nonsense
What is the result of missense mutations in hemophilia A?
produce a single amino acid substitution without a dominant negative effect resulting in an altered but partially functional protein product
Where do most missense mutations on the factor VIII take place?
What is the main cause of death in hemophilia A patients?
What % of hemophilia A patients are in the severe category factor VIII levels that are less than 1% of normal?
What is Duchenne Muscular Dystrophy (DMD)?
progressive weakness and loss of muscle one of the most severe and common forms
What is the genetic cause of DMD?
X linked recessive
What protein is disfxnl in DMD?
What is the role of dystrophin in the skeletal muscle cell?
Maintains the integrity
What is unique about deletions in the genome that causes color blindness?
They are caused by unequal crossover during meiosis
What is the most common X-linked mutation that causes mental retardation in males?
Fragile X syndrome