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36 Cards in this Set

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do males pass on their X chromosome to sons or daughters? Y chromosome?
daughters; sons
true or false. The X and Y sex chromosomes are approximately the same size.
false, the X chromosome has 155Mb while the Y chromosome has only 23Mb
what is the name for the product formed in the process of X-inactivation, an effort to equilbrate the amount of genetic material in males and females?
Barr body
at which point in development does X inactivation occur? Is one X normally chosen over the other for X-inactivation?
early in embryogenesis; no, both are inactivated without discretion in each cell
can the X chromosome chosen for a Barr body change with DNA replication and cell division?
no
do all cells in the female have the identical genetic identity?
no; they either have one X chromosome activated or the other. This is usually restricted to regions but is completely random
will a female heterozygous for an X-linked recessive disease gene manifest the disease?
usually not since each tissue in a woman's body will contain some cells that express the disease gene and others that do not (due to Barr bodies)
what appears to be the mechanism behind X-inactivation?
DNA methylation
what is the name for the gene in females which is present on the Barr body and is not present in males?
XIST
is the XIST transcript translated into protein? What is its role?
no; it is thought to induce inactivation through recruitment of unidentified silencing factors
genes in which region of the Barr body remain activated? What is the name for this region?
distal tip of the short arm; pseudoautosomal region 1 (PAR1)
what role does PAR play during meiosis?
X and Y chromosomes pair during meiosis at PAR
what must occur in females for them to have a phenotype for an X-linked recessive disease?
they must have the gene copy on each X chromosome defected
what is the term used for males in relationship to their X chromosome?
hemizygous
sex-linked recessive genes pass through the maternal or paternal side?
maternal since the males receive their X chromosome from the mother.
are males or females more commonly afflicted with a sex-linked recessive disease?
males
what percentage of the daughters of a man affected with a sex-linked recessive disease will be carriers for the gene? The daughter's sons?
none; 50%
can male-to-male transmission of sex-linked recessive disease occur?
no
are x-linked dominant disease more or less common than x-linked recessive disorders?
less
by how much are x-linked dominant diseases more common in females than in males?
two times
what is an example of a disease with a y-linked inheritance pattern?
there are none
what is heteroplasmy?
the fact that each mitochondrion contains multiple copies of DNA and that there are multiple mitochondria per cell and that mutations in DNA may only occur in one copy of DNA in one mitochondrion
how many genes are encoded by the mitochondrial genome? Does the mt genome have introns?
37; no
which tissues are usually most heavily affected by mitochondrial mutations?
tissues that require a higher level of mitochondrially produced ATP for normal function
what are 4 common mitochondrial diseases?
encephalopathy, myopathy, ataxia, and retinal degeneration
what is a new mutation?
when a child is born with a genetic disease and there is no previous history of the disease -- most prevalent with autosomal dominant diseases
what is mosiacism?
when a mutation occurs in an embryonic cell but not in all embryonic cells and the disease is thus limited to certain tissues in the body and not others
what is the implication of having part of the germ cells that have a mutation while having all somatic cell normal?
the individual is at risk for having more than one affected offspring while not expressing the disease him/herself
what is incomplete penetrance? What is an example of this?
when an individiual has the genotype for a disease but does not exhibit the disease phenotype at all although he/she can transmit the disease to the next generation; retinoblastoma
what is delayed age of onset?
when a disease is not expressed until adulthood which makes it difficult to assess the mode of inheritance
what is variable expressivity?
situation in which penetrance is complete but the severity of the disease may vary greatly among affected individual members of the same family who have the same mutation
what is locus heterogeneity?
a disease that can be caused by mutations at different loci in different families
what is allelic heterogeneity?
situation in which different mutations in the same gene result in variable phenotypes. These differences can be either minor or quite significant
which disease results from the unstable or dynamic mutations resulting from trinucleotide repeats?
Fragile X syndrome
as the number of trinucleotides increases in a person with fragile X mutation, does the likelihood of passing on the gene with a disease phenotype increase or decrease? Does the age of onset of the disease increase or decrease with each generation of Fragile X? what is the term used to describe this phenomenon?
increase; decrease; genetic anticipation
what is genetic imprinting?
when the maternal and paternal copies of the same gene are expressed differently