Sex-linked And Mitochondrial Inheritance Flashcards
Gene dosage:
The number of copies that we have of a gene
Mechanism for dosage compensation in women
X-inactivation
X-inactivation was hypothesized by:
Mary Lyon
X-inactivation is a ______ and _______ process
Random and permanent
X-inactivation is random except for cells that
Become the placenta, they inactivate the paternal X chromosome
Mosaic definition
Two different populations of cells, with either the paternal or maternal X chromosome inactivated
Hemizygous definition
One X chromosome which is expressed in all cells
Hypohidrotic ectodermal displasia is a ______ disease
X-linked recessive
Symptoms of hypoidrotic ectodermal dysplasia
Abnormal delvelopment of nails, hair or sweat glands greatly reduce ability to sweat
Barr bodies are:
Dense masses of chromatin present in interphase of female somatic cells that are not observed in male somatic cells
How many Barr bodies does a male have
Zero
How many Barr bodies does a female have
1
Turner syndrome has how many Barr bodies
XO = zero Barr bodies (female, cells look male)
Klinefelter syndome has how many Barr bodies
XXY = 1 Barr body, is male
Quintuple X syndrome has how many Barr bodies
4 Barr bodies, female XXXXX
X inactivation starts at the:
XIC which contains the gene XIST
XIST RNA is only expressed on the _____ X chromosome
Inactive
How does XIST RNA inactivate?
It inactivates itself by coating the inactive X chromosome
What helps to ensure the long-term stability of the inactivation of an X chromosome?
High methylation of DNA and histone hypoacetylation
About ____% of the genes on the X chromosome escape inactivation
15
Genes that escape X-inactivation: Why?
PAR1 and PAR2 regions (pseudo autosomal regions) because they behave more like autosomal genes
If there is only one active X chromosome in a cell, why would having extra or missing inactive X chromosomes present any problem?
X-activation is incomplete, resulting in altered dosages
There is no father to son transmission in ______ inheritance
X-linked recessive
Lesch-Nyhan syndrome is a ____________ disease
X-linked recessive disease
Lesch-Nyhan disease effects which gene
HGPRT (hypoxantine-Guanine Phosphoribosyl Transferase)
HGPRT gene is involved in:
The salvage pathway of purines
decreased HGPRT activity results in:
Increase in Uric acid (waste from not recycling purines)
Symptoms of Lesch-Nyhan syndrome:
Premature gout Kidney stones Decreased dopamine Low IQ Spastic cerebral palsy, dystonia Self-mutilation and aggressive behavior
gene mutation in Duchenne Muscular Dystrophy and Becker Muscular Dystrophy
dystrophin (present in muscle fibers)
What is the largest known human gene? How large?
dystropin, 2.5 million base pairs
Where is the dystrophin gene located
X chromosome
Duchenne Muscular Dystrophy and Becker Muscular Dystrophy specific type of mutation
Duchenne: small deletions leading to frameshifts
Bercker: larger deletions without frameshifts
What are grower’s signs
weakness of lower limbs, children have to leverage themselves standing up from the floor to compensate
dystrophin function in the cell
necessary to matintain the structural integriy of the cell’s cytoskeleton
What is a hallmark of an x-linked dominant inheritance
vertical transmission pattern, no father-to-son transmission
Why are X-linked dominant diseases less prevelent than X-linked recessive diseases?
decreased survivability and less likely ro reproduce
Rhett syndrome is a ______ disease
x-linked dominant
Why is Rhett syndrome more common in females?
usually lethal in males
Rhett syndrome specific mutations
various mutation of methyl-CpG binding protein 2 (MeCP2) which controls expression of genes in important brain functions
symptoms of Rhett syndrome
autistic behaviors, hand wringing, iltellectural disability, seizures, gait ataxia, heart rhythm and breathing abnormalities
variation in severety of Rhett syndrome is attributed to
skewed X-inactivation patterns
How is Rhett syndome typically transmitted
not in families, but in mutations. Except when females in earlier generations have X-inactivation skewed in favor of the X chromosome with the normal allele
Fragile X syndome effects which gene
FMR1 gene affects protein FMRP involved in cognitive development
Fragile X syndome is a __________ disease
X-linked dominant
symptoms of fragile X syndrome
itellectural disability, distinct facial appearance
Fragile X syndrome specific mutation
CGC repeat expansion in the promotor region of he FMR1 gene
trinucleotide repeat expansion leads to:
anticipation
Anticipation tends to occur when _______ pass the trait
female carriers
What is the “male determining factor”
SRY gene
The short arm (p) of the y chromosome has genes involved in:
bone growth
the long arm (q) of the y chromosome has genes involves with
azoospermia (sperm production)
regions of the sex chromosome that behave like autosomal chromosomes are called
pseudoautosomal regions
Langer mesolmelic dysplasia effects which gene
SHOX gene in the pseudoautosomal region
Leri-Weill dyschondrosteosis effects which gene
SHOX gene in psuedoautosomal region
Swyer syndome is a mutation of the ____ gene
SRY gene
syndrome where a genotypic male develops as a female
Swyer syndrome
46, XX testicular disorder of sex development results from:
translocation of the SRY gene onto an X chromosome. Develop as males with symptoms similar to klinefelter syndrome
How many genes are in mitochondrial DNA
37
mitochondrial DNA provides genes that are required for
oxidative phosphorylation
replicative segregation refers to:
random distribution of mtDNA between daughter mitochondria and random distribution of mitochondria between daughter cells
homoplasmy:
daughter cell received pure population of mitochondria all with normal or all with mutated DNA
heteroplasmy:
daughter cell received a mixed population of mitochondra, some with and some without mutated DNA
none of the offspring of an affected male will manifest the disease if the disease is:
a mitochondrial disease
All of the offspring of an affected female will inherit the disease if the disease is
a mitochondrial disease
