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33 Cards in this Set
- Front
- Back
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what is the Lyon hypothesis?
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that one of the X chromosomes is randomly inactivated in every one of a females somatic cells
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why are females considered mosaics?
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females have 2 distinct populations of cells with respect to the X chromosome and those cells are randomly grouped throughout the body. (calico cats)
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what can you see in a female nucleus that indicates the clumping and inactivation of the inactive X chromosome?
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a Barr body
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which gene is located at the XIC?
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the XIST gene
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what does the XIST gene do?
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encodes for mRNA that coats the X chromosome, inactivating it.
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what factors other than the XIST gene help to insure that the X chromosome is inactivated?
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methylation
hypoacetylation of histone |
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where are almost all sex linked genes located?
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On the X chromosome.
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why do males always express a sex linked disease?
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because we only have one X chromosome and therefore, must express the gene.
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what are the 3 guidelines for determining a sex linked mutation for X-recessive diseases?
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1. more frequent in males
2. no father to son transmission 3. the disease can skip generations |
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what are the X linked recessive diseases mentioned?
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Hemophilia A and B
Lesch-Nyhan synd Duschenne muscular dystrophy red green color blindness severe combined immunodeficiency ornathine transcarbamylase deficiency |
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is red green color blindness more common in males or females?
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males
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what is red green color blindness usually caused by?
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aberrant recombination of opsin genes
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which is more common, Hemophilia A or B?
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A is 5 times more common than B
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which coagulation factors are affected in hemophilia?
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A: VIII
B: IX |
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what causes the severity of hemophilia to vary?
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the amount of coagulation factor made
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which gene does duschenne muscular dystrophy affect?
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the dystrophin gene
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what are the effects of DMD?
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skeletal muscle weakens, is lost, and then replaced by fat
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what is unique about the dystrophin gene?
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it is the largest gene in humans
2.5 million base pairs |
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what does the dystrophin protein do?
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maintains the integrity of muscle cells cytoskeleton
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what is the difference between Becker muscular dystrophy and DMD?
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Becker has a partially functioning dystrophin protein
Duschennes dystrophin protein is completely absent |
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Are females affected by DMD?
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usually not, but if they do have symptoms they are very mild.
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what is the x linked dominant disease discussed in lecture?
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fragile X syndrome
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what are the symptoms of fragile X syndrome?
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mental retardation
long face, large ears hypermobile joints increased testicular volume (macroorchidism) |
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what is fragile x syndrome caused by?
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a trinucleotide expansion repeat in the FMR1 gene
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what are the 4 characteristics of x linked dominant diseases?
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1. no father to son xmission, but all daughters are affected
2. females are twice as likely to be affected, but the expression is less severe in female heterozygotes 3.typical mating is between a normal male and heterozygous female 4. vertical transmission pattern |
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what is a sex influenced trait?
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a trait that is not X linked, but predominates in a particular sex due to phisiological differences
(male pattern baldness) |
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what is a sex limited trait?
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a trait only expressed in one sex, but is due to anatomical differences
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how many genes are encoded in the mitochondrial genome?
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37
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what are the unusual features of mitochondrial DNA?
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replicative segregation
homoplasmy and heteroplasmy maternal inheritance |
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why is mitochondrial DNA only maternally inherited?
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because sperm cells only contain a few hundred mitochondria while Oocytes contain 200,000
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what is replicative segregation?
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random distribution of DNA copies in daughter cells
random distribution of mitochondria in daughter cells |
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what are the 2 characteristics of mitochondrial inheritance?
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1. only females can transmit the disease
2. both males and females can be affected |
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what are the 7 mitochondrial diseases?
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MERRF
MELAS LHON CPEO pearson syndrome leigh syndrome Kerns-sayre syndrome |
