Test 2 Flashcards
What is a somatic cell?
cell with two copies of chromosome. Not gametes
What is an autosome?
chromosome that is not a sex chr.
What is an allosome?
sex chr. (X/Y)
What is a homologous chr?
consists of 2 chr in a diploid, where 1 is maternal and 1 is paternal
What is allelic heterogeneity?
alleles of different origin
What is locus heterogeneity?
locus that consist of different origin.
What is a polymorphism?
A natural DNA variation that accumulate within an allele.
What is hemizygous?
only 1 copy of chr is present in a diploid. Diploid loses 1 copy of chr.
What is pleiotropism?
effect where 1 gene mutation can lead to 2+ phenotypic genetic mutations.
What is an example of pleitropism?
occulodentodigital dysplasia
How do you describe incomplete dominance?
both allele types are expressed leading to phenotypic expression of both the dominant and recessive expression
What is codominance?
this occurs when both the dominant and recessive alleles are expressed.
what does a box represent on a pedigree?
box=male
what does a circle signify on the pedigree?
circle = woman
An autosommal dominant gene will express how?
- equal m/f affect
2. carried through all generations
What is common of autosommal recessive gene expression?
- equal m/f affected
2. tendency to skip generations
What is common of X-linked recessive?
- X-linked= no m-m transfer
- F–>M causes affected M always
- tendency to skip generation
What is common of X-linked dominant?
- M–>M not seen
- present in all generation
- all women are affected
An affected male produces a son with no genotypic defect, but all 4 daughters contain the defect, what is most likely the inheritance pattern? assume mother is unaffected.
X-linked dominant.
- X-linked recessive would occur if not ALL the daughters were affected.
What is haploinsufficiency?
- a giploid loses 1 gene, and the phenotype is based on only remaining gene. Can be seen with unaffected parents, but the defect is inherited down the pedigree.
What is penetrance?
the frequency to which an allele is expressed in a phenotype.
An individual is told they are at a 75% chance of developing cancer due to a mutation of RB gene. What is the pentetrance of that gene?
penetrance is 75%. If 100 people had a mutated RB gene then 75 would be at risk for cancer development.
What is incomplete penetrance?
This occurs when individuals carry the allele that normally causes disease but have no presentation of the disease and appear fine.
How does X-inactivation occur?
- somatic cells are methylated forming heterochromatin, which begins at blastocyst formation.
- leads to formation of barr bodies
What is random X-inactivation?
equal probability of either paternal or maternal allele silencing
What is fixed X-inactivation?
this occurs when an allele is silenced and that same allele remains silenced throughout downstream generations.
What is incomplete X-inactivation?
- some regions of the chromosome are not completely inactivated and this leads to presentation similar to X-linked recessive.
What are the main consequences of enzyme deficiency?
- substrate accumulation (could be toxic to cells)
- reduced product formed(multiple effects)
- inability to regulate toxins or inability to control zymogens
What is a germline mutation?
this mutation could become present in every cell of the offspring, as the mutation affects the gamete producing genes.
What are the most likely outcomes of a germline mutation?
- reduced fertility
2. high mortality
What is unique about trinucleotide repeat mutations?
- the symptoms of the mutations will continue to be seen more and more early in life as the mutation progresses to further generations.
A trinucleotide repeat mutation, adding CGG is commonly referred to as____?
fragile X syndrome
What leads to Fragile X syndrome?
trinucleotide repeat mutation of CGG
A trinucleotide repeat mutation, adding CTG leads to what disease?
Myotonic dystrophy
Myotonic dystrophy is a result of what?
CTG trinucleotide repeat mutation
A trinucleotide repeat mutation of CAG leads to what disease?
Huntington’s disease
Huntington’s disease is characterised by what DNA sequencing?
trinucleotide repeat of CAG
What process occurs that produces trinucleotide repeat mutations?
- replicate DNA strand detaches and loops form at CG rich regions
- the looped region is then re-synthesized
- the CG rich loop then unloops and rebinds to DNA strand leading to multiple repeats.
What is unique of mitochondrial genes?
- majority code for mRNA/tRNA formation
2. 13 are for respiratory chain.
How would mitochondrial mutations be expressed on a pedigree?
- all offspring from an affected mother would be affected.
Trisomy are a very common example of what type of mutation?
- aneuploidy is the result
but mosaicism
What is mosaicism?
- presence of 2 different genotypes in a person developed from one zygote.
- can be somatic (trisomy 21) or gonadal
What is a chimera?
person who contains different cell types that were produced in separate zygotes.
- seen in twins where one zygote engulfs the other.
How does a ring chromosome form?
- the ends of chromosome are deleted and the “new ends” link up to form a ring, that can’t be replicated/
What is a common disease seen with ring chromosomes?
epilepsy
What is paracentric inversion?
- the gene sequences on a chromosome invert but do not cross the kinetocore
What is pericentric inversion?
the gene sequences of a chromosome invert by flipping over the kinetocore.
What is the best explanation of balanced chromosome translocation?
- equal portions of material are exchanged among the p and q arms
What is unbalanced translocation?
uneven material exchange among the p and q arms
What is the Robertsonian translocation?
- material between 2 normal chr is switched.
- produces one Xlong chr, and 1 Xshort chr.
- the Xshort is lost–> producing person with 45 chromosomes.
What are common chromosomes that undergo robertsonian translocations?
13, 14, 15, 21, 22
What is uniparental disomy?
occurs when either Mother/Father donate both chromosome copies to offspring.
What are the two methods that can cause disomy?
- heterodisomy: the pair is inherited from one parent.
2. isodisomy: 1 chromosome is inherited form 1 parent, and Meiosis II error replicates the chromosome.
What is the significance of uniparental disomy?
- leads to genomic imprinting.
2. isodisomy more commonly leads to expression of recessive genes.
What is a linkage disequilibrium?
a single nucleotide polymorphism that is inherited due to its close proximity to a diseased gene
What are restriction fragment length polymorphisms?
- regions on DNA that endonuclease cleave at. produce variety of DNA strand lengths.
How can restriction fragment length polymorphisms be helpful?
- compare a normal person to diseased person and look for differences. altered chain lengths correspond to altered # of RFLP.
What analysis methdos are used to analyze the different lengths of the RFLP?
Southern blot= DNA
Northern blot=RNA
western blot= protein
What is a microsatellite repeat?
- polymorphism repeat unique to individuals. often called short tandem repeats.
- used for forensic testing.
- (2-6) bp long
What is a minisatellite repeat?
also short tandem repeat used for forensic analysis.
2. 70bp long
What are common variable number tandem repeats?
- microsatellites
2. minisatellites.
What are copy number variatiants?
- these consist of varying lengths of repeating nucleotide sequences.
- lengths vary among individuals
- commonly seen as trinucleotide repeat sequences–> disease
What is the difference between linked and unlinked genes?
- linked: close proximity generally inherited together and do not undergo recombination
- unlinked: generally large separation and likely to undergo recombination before inheritance together.
What does the hardy weinberg rule state?
that alleles will remain the same in a large population with natural selection, random mating, and no mutation or genetic drift occurring.
What is the founder effect?
occurs when small group of individuals leave a large group, establish their own group and have an INCREASE expression of recessive genotypes.
What is natural selection?
The increased allelic frequency seen in animals that survive various environmental challenges.
What type of disease is more common in natural selection events?
dominant types
What is genetic drift?
a change in the population’s allele frequency resulting from a random variation in the distribution of alleles from one generation to the next
What type of populations are affected teh most with genetic drift? The least?
- most: small population
2. least: large population.
What type of laboratory testing can be used to locate SNP?
- allele-specific oligonucleotide probe.
- nucleotide sequence base pairs with complementary strands that produces a hybridized DNA strand based on the SNP you are looking for. - The probe complements the strand you want to identify.
