52 terms

Biology 1700 Chapter 15

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True or False: The genotype of an organism constitutes is observable characteristics.
false
True or False: Much of the genetic variation seen in the human population is neutral.
true
True or False: Saying that a SNP is associated with a particular disease means that if you possess that particular SNP, you will end up with that disease.
false
A person has the genotype XXY. What syndrome does this person have and what sex are they?
Klinefelter....male
Phenotypes:
can be subject to environmental conditions
True or False: Variable tandem repeats and restriction fragment length polymorphisms are synonymous―both consist of repeated fragments of DNA with the same sequence (i.e., GTAGTAGTA).
false
True or False: Genotyping microarrays can determine if a chromosomal mutation at a given locus is due to a duplication.
false
True or False: There are no discernible phenotypic effects for an individual with the genotype XYY.
true
Up until 20-30 years ago, people with cystic fibrosis (CF) wouldn't live long enough to reproduce. CF is a homozygous recessive condition, leading researchers to think that over time the incidence of CF would decrease because the allele would be removed from the gene pool. The results actually indicate that the rate of CF is on the rise. Based on what you know about why certain genotypes and phenotypes persist in a population, what is a likely explanation for why the rate of CF is on the rise?
The heterozygous condition is beneficial, much like what we see with sickle cell trait.
Short repeated sequences of DNA that vary in number from one chromosome to the next are called:
variable tandem repeats.
True or False: In microarrays, the oligonucleotides that are attached have the fluorescent tag, whereas the DNA fragments being tested do not.
false
True or False: Nondisjunction in the sex chromosomes is more severe than in the autosomes.
false
Imagine that you know two sisters―Rose and Sam―both of whom smoke. Furthermore, Rose has a mutation in the gene for alpha-1 antitrypsin, whereas Sam does not. What is true regarding these sisters?
It is possible that neither Rose nor Sam will develop emphysema; however, the fact that both sisters smoke―added to the mutation that Rose carries―increases their chances of developing this disease.
You are working in a medical research lab and have to determine if a patient is heterozygous or homozygous for a particular restriction site. You isolate a region of DNA from each chromosome, the middle of which could contain the restriction site, if the patient has it. If you treat the DNA with the restriction enzyme, how many fragments will be produced if the patient is heterozygous for the presence of the restriction site?
three
True or False: The biggest difference between CNV and VNTRs is the size of the DNA being studied.
true
True or False: Nondisjunction is when sister chromatids fail to separate during anaphase of cell division.
true
Genetic studies have identified an allele (Δ32) that seems to provide protection against AIDS. Which of the following would most likely explain the reason why our population has this mutation?
This mutation likely benefited the human population against some other early pathogen.
True or False: Only polymorphisms that add or remove restriction sites can be useful in DNA typing.
false
True or False: A single nucleotide polymorphism (SNP) and a point mutation are the same thing.
false
True or False: Trisomy 21 (Down syndrome) is the only example of an autosomal trisomy in which the fetus develops to term and is born alive.
false
True or False: A phenotype always refers to something that you can see with your eyes, like hair color or eye color.
false
True or False: VNTRs and RFLPs are remarkably rare within the human genome―the majority of human polymorphisms take the form of point mutations, and these are most often used for DNA typing.
false
The difference between a single nucleotide polymorphism (SNP) and a point mutation is that:
a point mutation is when a base pair is changed to a different base pair, whereas a SNP is when the base pair differs among individuals in a population.
In mammals, females have two copies of the X chromosome, whereas males have only one copy. Dosage compensation is accomplished in mammals by:
females possessing a randomly inactivated X chromosome in all cells.
True or False: While a mutation will not always change the phenotype of an individual, it will always change the genotype.
true
What does "RFLP" stand for?
restriction fragment length polymorphism
Which of the following statements explains why restriction enzymes are not useful for genome-wide studies of genetic variation?
Using restriction enzymes will only tell us differences in sequence variation in restriction sites.
A new gene is discovered that dramatically aids in the digestion of fish. You hypothesize that populations with a history of being near the shoreline would have more copies of this gene than populations found farther inland. What technique would you use to test this?
genotyping microarray
If an individual is homozygous for a certain trait, it means that:
the individual received the same allele from each parent.
Which of the following is an advantage of DNA typing?
Only small amounts of DNA are needed.
What is used for DNA typing?
-PCR
-gel electrophoresis
-VNTR
-RFLP
After doing PCR on the same region between two individuals, you notice that each person's DNA yielded pieces of different sizes. What is the most likely explanation?
This is an example of VNTRs.
True or False: Some alleles in the heterozygous state are beneficial, whereas in the homozygous state they are harmful.
true
SNPs within a gene called FOXO correlate with increased longevity in humans. You are a researcher in a lab and wish to determine if you possess this SNP. What technique would allow you to accomplish this?
genotyping microarray
A microarray:
is a method that detects a single SNP.
A patient is about to receive chemotherapy and the doctor is concerned with dispensing the correct dosage. Certain people cannot metabolize this type of chemotherapy because they have a SNP in one particular gene. What test could be performed that would let the doctor know if her patient can handle this type of chemotherapy?
gentoyping microarray
The number of tandem repeats in an individual:
will vary from chromosome to chromosome
Which of the following explains the difference between VNTRs and RFLPs?
In VNTRs, we are looking at the number of times a sequence is repeated; in RFLPs we are looking at size differences resulting from different restriction sites being present.
Sickle Cell Anemia
3 alleles of -globin
A = wt
S = sickle
C = mildly affected protein
Understand effects of various genotypes (both homozygous and heterozygous) on phenotype
How does environment influence phenotype - HINT: malaria
Emphysema
Example of a disease affected by both genotype and environment
Genetic component - PiZ allele of 1AT
This mutant does not work well to inhibit elastase
Elastase degrades elastin
Leads to diseased lungs
Environmental component - cigarette smoking
Smoking inhibits 1AT
Similar result to above
Both PiZ and smoking - even worse
Develop emphysema early - often die young
Beneficial Mutation
Example is deletion mutation in CCR5
Causes a frameshift leading to early stop codon
HIV cannot bind and therefore can't infect CD4+ T cells
Homozygotes for CCR5 mutant rarely develop AIDS
VNTR
variable number of tandem repeats
-Individuals have different number of short (a few bases) repeat sequence of DNA
-Can be used to tell individuals apart genetically (ex. crime scene)
PCR to amplify segment of chromosome
Examine by electrophoresis to look for different sized PCR products
RFLP
restriction fragment length polymorphism
-ndividuals have differences in location of restriction sites
-Can also be used to tell individuals apart
-Example is sickle cell anemia - mutation disrupts restriction site
PCR region with mutation
Cut with restriction enzyme
No cut = S allele
SNP
- single nucleotide polymorphism
-Change in one base (point mutation) that is common in population
-Cause much of the variation in individuals
-Example is blue eye color
CNP
copy number variation
-Repeats of a large segment of a chromosome containing 1 or more genes
-Example is AMY1
More copies of this gene in a population that needs it
Extra or missing chromosomes:
-Caused by non-disjunction (chromosome fail to separate at anaphase in meiosis)
-Effects usually severe - most fetuses spontaneously abort
-Some are less severe
Examples
Down Syndrome
3 copies (trisomy) of chromosome 21
Sex chromosomes
XXY - Klinefelter Syndrome
X - Turner Syndrome
genotype
genetic makeup of an individual (what actual genes the organism has)
polymorphism
any mutation common enough to appear once in 50 individuals
allele
different forms of a given gene
heterozygous
having two different alleles of a given gene
homozygous
having two identical alleles of a given gene
phenotype
the observable expression of a trait. It is affected by genotype and environment