Lec 6. Extensions to Medels Rules Flashcards Preview

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Y-Linked characteristics are only present in



Why is the Y chromosome so small compared to the X chromosome?

Y chromosome lost DNA over time


What is important for the sex determination in SRY?

Y chromosome


What is the theory of the origin of the Y chromosome?

Evolved from an ordinary pair of autosomes but over time the Y chromosome lost genes.


What are four example of Y linked diseases?

Male infertility, Hypertrichosis pinnae (hairy ear), Retinitis pigmentosa, XYY syndrome


What is the XYY syndrome?

male has an extra Y, having 47 chromosomes. Causes increased height, learning disabilities, aggressive acne, aggressive behavior.


What happens if the SRY gene gets translocated?

Gets stuck on the X chromosome making the males XX. Results in infertility.


Where do sex linked traits usually originate from?

on the sex chromosome, usually the X


What is X-linked recessive inheritance?

Mutation in a gene on the X causes the phenotype to be expressed in males.


What is dosage compensation?

Inactivation of 1 X chromosome to compensate for different X dosage between the sexes.


What is the Lyon Hypothesis?

Suggests that dosage compensation in mammals is by inactivation of all but one X chromosome in cells with more than one X chromosome. Ex: bar body.


What is Mosaicism?

Condition in which cells within the same person have a different genetic makeup. Ex: when different X chromosomes are inactivated in neighboring cells.


What is Xic?

X inactivation centers are counted


How does X inactivation work?

If two or more X chromosomes are present, Xist is turned on, and its RNA product coats one of the X's RANDOMLY.


When is the X inactivation process undone?

During meiosis


List the most common X-linked recessive disorders

Red-green color blindness, Hemophilia A&B, Duchenne & Becker's muscular dystrophy, X-linked Ichthyosis, XLA, and Glucose-6-phosphate dehydrogenase deficiency. Fragile X.


What is Hemophilia A?

blood clotting disorder caused by a mutation of the Factor VIII gene. Most common


What is Hemophilia B?

A blood clotting disorder caused by a mutation of the Factor IX. Least common


Duchenne muscular dystrophy is associated with what gene mutation?



Which X-linked recessive disorder is a milder form of Duchenne?

Becker's muscular dystrophy


What is X-linked ichthyosis?

a form of ichthyosis caused by a hereditary deficiency of the STS enzyme


What is X-linked agammaglobulinemia (XLA)?

these pts dont generate mature B cells.


What is glucose-6-phosphate dehydrogenase deficiency?

Causes nonimmune hemolytic anemia in repsonse to a number of causes, most commonly infection or exposure to certain medication, chemicals, or foods.


Can a male cat ever be calico?

Yes, XXY


True or False? Hemophilia A and B are X linked and usually inherited from a Male carrier

False. Usually carried from a Female carrier.


Approximately 1/3 of women carrying the hemophilia gene experience bleeding episodes why?

Random x inactivation and random bad luck that the bad chromosome got copied


A woman who is red/green color blind has children with a man with normal vision. What is the probability that their 1st child will be color blind?

1/2 because Mom is going to produce gametes that have the defective gene that have color sensitivity. All of her kids will get the X chromosome but the dad will also give his X, thus 1/2. All females will not be color blind but all males will be colorblind.


What are Mendel's three laws?

Principle of segregation, independent assortment and concepts of dominance and recessive.


True or False? There are no exceptions in Mendel's laws

False. There are some exceptions.


What is an exception to independent assortment?

Genes on the same chromosome are linked and may NOT segregate independently