MOL GEN 4500 final exam long answers (6pts)
List at least two different types of DNA repair and briefly explain how each is carried out.
(any 2 of the following): 1. Mismatch repair; replication errors that are the restult of base-pair mismatches are repaired. Mismatch repair enzymes recognize distortions in the DNA structure due to mispairing and detect the newly synthesized strand by the lack of methylation on the new strand. The bulge is excised and DNA polymerase and DNA ligase fill in the gap 2. Direct repair; DNA damage is repaired by directly changing the damaged nucleotide back to its original structure 3. Base excision repair; the damaged base is excised, and then the entire nucleotide is replaced 4. Photo reactive repair; the reversal of pyrimidine dimers formed by UV light exposure. Requires the photoactivation enzyme 5. Post-replication repair; occurs on damaged DNA that has escaped initial mismatch repair during DNA replication. In this mechanism the RecA protein recombines the corresponding on the undamaged parental strand of the same polarity 6. Double strand break repair; responsible for attaching two broken strands of DNA - uses homologous recombination repair and the corresponding region on the sister chromatid as a template
Huntington's disease is a late-onset disease caused by a single, dominant mutation. The following pedigree is for a family width a history of Huntington disease. Those individuals who are already suffering form the disease are shaded black. However, some additional individuals in generations II and III also have the Huntington allele and will develop Huntington disease but have not yet shown symptoms. Assume that individuals marrying into the family have no history of the disease (homozygous recessive for the gene). Also assume that the diseased male in generation I is heterozygous for the disease. (i) What is the probability that the male IIIa carries a Dominant Huntington allele? (ii) What is the probability that the female IId carries the Dominant Huntington allele? (iii) If IIIa and IIg have a child, what is the probability that the child would receive the Dominant Huntington allele
(i) 1/4 (ii) 1/2 (iii) 1/8
How will variation for a gene in a given population be increased?
If migration from other populations brings into the recipient population gene alleles that are not already in the population or are present at a lower frequency.
Nucleic acid blotting is commonly used in molecular biology. Two types, Southern blots and norther blots, involve gel electrophoresis and a filter, which holds the nucleic acid. Briefly describe the procedure of "blotting" in this context and differentiate between Southern and northern blots.
In a Southern blot the DNA to be "probed" is cut with a restriction enzyme(s); then the fragments are separated by gel electrophoresis. Alkali treatment of the gel denatures the DNA, which is then "blotted" onto the filter (nylon or nitrocellulose). A labeled probe (RNA or DNA) is then hybridized to complementary fragments on the filter. In a northern blot, RNA is separated in the gel and "probed" with the labeled DNA.
Explain how inbreeding can have a positive effect on population fitness.
Many deleterious recessive alleles are weeded out by natural or artificial selection so that the population becomes homozygous for beneficial alleles. In this way, the harmful effects of inbreeding may eventually be eliminated leaving a population that is homozygous for beneficial traits.
Explain how it is that genetic variation is maintained in the population. Why is it that dominant alleles do not eventually take over?
Meiotic segregation in randomly mating populations results in an equilibrium distribution of genotypes after only one generation, so genetic variation is maintained. As long as there is random mating occurring, then the frequency of dominant and recessive alleles will remain the same.
Monod discovered that if tryptophan is present in relatively high quantities in the growth medium, the enzymes necessary for its synthesis are repressed. How does this occur?
Tryptophan acts as a corepressor to activate the tryptophan repressor protein; it is also involved in an attentuation system, which causes the termination of transcription.
The following pedigree is for a family with an autosomal recessive genetic disease. (i) Identify the possible genotypes of all individuals in the pedigree. Note that some individuals cannot be definitively determined - for each of these individuals, list the phenotypes they might have. (ii) From the above pedigree, if individuals labeled 2 and 3 are both carriers, what is the probability that they will produce an affected offspring? (see picture on google doc)
(i) Going from left to right in the pedigree: Generation 1: Aa, Aa (produced an affected offspring so they must be carriers of the recessive mutation) Generation 2: Aa, aa, AA/Aa, aa, Aa Generation 3: Aa, aa, Aa, Aa, aa (ii) If 2 and 3 are carriers, then they have genotypes of Aa respectively. They have a 1/4 chance of producing an affected offspring.
List the three basic components required for bacterial cloning vector and briefly describe the purpose of each
-origin in replication for propagation in the host -selectable marker like Amp resistance -polylinker or unique restriction enzyme sites to facilitate cloning
The following table shows several bacterial strain lac operon genotypes (some are partial diploids). Fill in the blanks in the "lactose absent" and "lactose present" columns in this table. (+) means significant levels of active ß-galactosidase enzyme can be detected. (-) means no significant levels of active ß-galactosidase enzyme. Label your answers: Lactose absent #1-6 and Lactose present #1-6 Strain Geno Type Lac Abs Lac pres 1. lacI+ lacP+ lacO+ lacZ+ lacY+ 2. lacI+ lacP+ lacOc lacZ+ lacY+ 3. lacI+ lacP+ lacOc lacZ- lacY+ 4. lacIs lacP+ lacOc lacZ+ lacY+ 5. lacI- lacP+ lacO+ lacZ+ lacY+ / lacI+ 6. lacIs lacP+ lacO+ lacZ+ lacY+/ lac I+
1. - + 2. + + 3. - - 4. + + 5. - + 6. - -
Describe 3 pieces of evidence that supports the hypothesis that DNA methylation is important factor in gene regulation
1. An inverse relationship exists bw the degree of methylation and the degree of gene expression 2. Methylation patterns are tissue specific and heritable for all cells in that tissue 3. Incorporation of 5-azacytosine (which can't be methylated) causes changes in the pattern of gene expression.
One of the dominant features of the immune system is the capacity to generate new cells that contain different combination of antibodies. Because there are billions of combinations it is impossible for each combination to be encoded by a single gene. Explain in sufficient detail how such diversity is accomplished in the case of the light chain of a typical antibody.
1. It is achieved by the process of somatic recombination: 2. One of 70-100 L-V segments joined to one of 6 J regions. 3. Recombination to J region is imprecise over a 6 bp region. 4. Break and nibble mechanism adds or removes bases during this recombination process. 5. Introns spliced out 6. Translation produces light-chain polypeptide 7. Leader polypeptide removed, producing mature light chain.
Answer the following questions about standard PCR: 1. What enzyme is required for PCR? State the specific name of the enzyme, not just the type of enzyme. 2. Apart from the enzyme, what 3 DNA molecules are required (give the technical names by which they are called)? What must be true about the sequences of these molecules? Note that dNTPs are individual nucleotides, not DNA molecules. 3. Name the three basic steps of PCR and describe the molecular processes that occur in each. How is each step induced? 4. How does this system work to amplify DNA?
1. Taq polymerase 2. 2 primers, 1 template, dNTPs. The primer sequence must be complementary to the ends of the sequence to be amplified 3. Denaturation: Temperature is raised to ~94 C. Strands of DNA separate Annealing: The temperature is lowered to 50-65 C. Primer strands anneal to the template strand. Extension (or elongation): The temperature is raised to ~72 C. Taq polymerase synthesizes a complementary DNA strand form dNTPs. 4. The amount of DNA is doubled in each reaction, so that after (for example) 30 cycles, it has increased by a factor of 2^30.
Define polymorphism.
A gene or a trait is said to be polymorphic if there is more than one form of that trait in a population.
Why is a karyotype done at metaphase of the cell cycle? Specifically, what is being observed at this point in the cell cycle?
A karyotype is a picture of a squash of chromosomes taken at metaphase of the cell cycle (following DNA synthesis) bc that's when condensations of the chromosomes has taken place prior to segregation to daughter cells. At other times in the cell cycle, the chromosomes would not be visible. Specifically, we are observing two sets of "sister chromatids" for each chromosome bc the photograph is taken after DNA synthesis has occurred but before chromatid separation happened.
Three human disorders- fragile X syndrome, myotonic dystrophy, and Huntington disease - are conceptually linked by a common mode of molecular upset. Describe the phenomena that links these disorders.
All 3 are caused by disparate genes, but each gene was found to contain repeats of a unique trinucleotide sequence. Additionally, the number of repeats may increase in each subsequent generation (genetic anticipation).
Describe alternative gene splicing. What is the result of the alternative splicing mechanism?
Alternative splicing is differential splicing of alternative exons from an initial pre-mRNA transcript. The result is that the possible proteins that a cell can produce (its proteome) is far larger than the number of genes in the genome.
Kornberg used the phage PhiX174 to demonstrate DNA pol 1 was able to produce biologically active DNA in vitro. Describe in sufficient detail the experimental methods that he used to draw the conclusions in DNA pol 1 could produce biologucally active DNA. For full credit include details about any reagents, chemicals, or labels that Kornberg utilized in order to draw his conclusions.
An initial (+) strand of PhiX174 was labeled w/ 3H, this was added to DNA pol 1, ligase, bromouracil and 32P labeled dNTP to produce (-) strand. The dsRF was nicked, made single stranded, and the new (-) strand was isolated following centrifugation. The (-) strand was then used with DNA pol 1, ligase, unlabeled dNTPs, and NO BU, to produce a new (+) strand in vitro. This new (+) strand was successfully used to infect E. coli and produce new PhiX175 phage particles. This demonstrated that DNA pol 1 was capable of producing biologically active DNA in vitro.
What is evolution? Describe four different mechanisms by which it can occur.
Answer: Evolution is a change in the allele frequencies in a population. It can occur via the following four mechanisms: a) Genetic drift. Conditions under which it occurs: Random change in allele frequencies due to small population size or a small founder population colonizing a new habitat. b) Migration/gene flow. Conditions under which it occurs: New individuals are added to a population. If their genetic makeup for any particular gene is different from that of the population they join, the overall allele frequency in the new population changes. c) Mutation. Conditions under which it occurs: A direct change in an allele as a result of some environmental insult and/or a problem in replication. d) Natural selection. Conditions under which it occurs: If there is variation for a trait, heritability for that trait, and differential reproductive success based on that trait, evolution by natural selection is occurring.
Briefly define the term "autoradiography." Identify and describe a classic experiment that used autoradiography to determine the replicative nature of DNA in eukaryotes.
Autoradiography is a technique that allows an isotope to be detected within a cell. The Taylor, Woods, and Hughes (1957) experiment used 3H-thymidine.
What experimental methods led Avery, McCarty, and Macleod to determine that DNA was the "transforming material" in their classic experiment? Be as specific as possible in your answer for full credit.
By first removing proteins they still got transformation in vitro. Next they removed RNA and still got transformation. However, when they degraded DNA they no longer got transformation, therefore they concluded that DNA must be the transforming material.
We discussed cis regulatory elements (CRMs) in transcriptional networks. What are CRMs and how are they involved in gene regulation?
CRMs are DNA sequences found within the introns and/or upstream or downstream of genes. They consist of a few hundred base pairs that contain binding sites for transcription factor proteins that are involved in activating (or repressing) transcription of the genes that they are located adjacent to.
Explain at least TWO reasons why the following definition of a gene is incomplete: "A gene consists of DNA sequences that encode a single polypeptide"
Definition does not include: 1. Regulatory sequences 2. Not all genes are DNA sequences 3. Not all genes transcribe a single RNA molecule 4. Not all RNA molecules encode for a single polypeptide
Define the term "fitness". What are three critical points to keep in mind when measuring fitness?
Fitness is the relative probability of survival and reproduction of a genotype or phenotype. Critical to assessing fitness is understanding that it is measured: a) relative to other genotypes/phenotypes in the population; b) in a specific environment; c) by reproductive success.
You have embarked on some additional heteropolymer experiments to further evaluate the codon table. In your current heteropolymer experiment you are using guanine and uracil to produce a synthetic mRNA using the enzyme polynucleotide phosphorylase to make the synthetic mRNA. You are using these two ribonucleotide diphosphases in the following ratio, 3G:5U. Using the information, what are ALL of the expected triplets produced in this experiment? Further, what are expected percentages of each of these triplets in the synthetic mRNA?
GGG: 5.3% GGU: 8.8% UGG: 8.8% GUG: 8.8% GUU: 14.6% UGU: 14.6% UUG: 14.6% UUU: 24.4%
How does genetic drift alter the genetic variation in a population? Why is it a relatively insignificant agent of evolution in all but the very smallest populations?
Genetic drift, one of four agents of evolution, is characterized by a random change in allele frequencies. Because in altering allele frequencies it can produce fixation of one allele or another, genetic drift decreases the genetic variation in a population over time. There is a probabilistic component to fertilization—it is not certain which sperm and/or egg will be involved—and, consequently, the outcome of crosses cannot always be predicted with accuracy. For example, when a homozygous recessive individual (such as for blue eyes: bb) is crossed with a heterozygote (for brown eyes: Bb), we expect half of the offspring to be heterozygous and half to be homozygous recessive. It is conceivable, however, that all of the offspring (say two or three or more offspring in a row) could be homozygous recessive (and blue-eyed). This can lead to a change in the population's allele frequencies. Just as likely, though, would be for all of the offspring of a cross to be heterozygous (and brown-eyed), again altering the allele frequencies but this time in the opposite direction. The larger a population is, the more likely that any deviations in one direction from our expectations are offset by deviations in the other direction. When this happens, the net effect is that the allele frequencies do not change. For this reason, genetic drift generally plays a significant role only in very small populations.
The catabolite repression system in E. coli essentially represses the lac operon when glucose is present. What evolutionary advantage would favor the evolution of such a system?
Glucose can enter glycolysis "as is," while lactose must first be split into glucose and galactose. To do this, the energy requiring synthesis of B-galactosidase is needed. It is energy efficient to burn glucose rather than lactose.
Describe the structure of a helix-turn-helix (HTH) motif. What is the general function of such motifs?
HTH motif were the first DNA-binding motifs identified. A geometric conformation is formed by two adjacent alpha helices separated by a "turn" of several amino acids. They bind to the major grooves of DNA and interact with the DNA backbone. Many HTH-containing proteins regulate gene expression.
What is unusual about the amino acid composition of histones? How is the function of histones related to the amino acid composition? Of which histones are nucleosomes composed?
Histones contain large amounts of positively charged amino acids such as lysine and arginine. Thus, they can bind electrostatically to the negatively charged phosphate groups of nucleotides. Nucleosomes are composed of all histones except H1.
What are homeotic genes and what do they do?
Homeotic genes are important in development of higher level organism. They play an important role in segmentation of the body parts, They determine the fate and body part segmentation. Mutations in these genes can result in body parts on the wrong segment of the body.
Describe the difference between meiosis I and meiosis II
Homologs pair and segregate in meiosis I. Sister chromatids are paired and segregate in meiosis II. Crossing over occurs in meiosis I but not in meiosis II
Assume that a new mutation occurs in the germ line of an individual. What finding would suggest that the new mutation is dominant rather than recessive?
If dominant and if passed on to the next generation, it would be expressed. New recessive mutations are not normally passed on in the next generation, unless, through a combination with a like mutation from the other parents, they are homozygous.
You are studying a population of kangaroo rats. You calculate the expected frequencies of the alleles for coat color. When you compare these to the observed genotype frequencies, there is a large discrepancy. What can you deduce, based on these findings?
If the expected genotype frequencies and the observed genotype frequencies are very different, then the population is not in Hardy-Weinberg equilibrium. At least one of the assumptions must be being violated.
Describe two mating patterns that have an impact on the genetic composition of a population.
Inbreeding—preferential mating with close relatives Assortative mating—preferential mating with individuals of dissimilar or similar genotype or phenotype.
What do kinase enzymes do to other proteins? In what ways can this activity affect the function of these proteins?
Kinase enzymes act by phosphorylating (adding a phosphate) to other proteins. This has an effect on the phosphorylated protein by changing that protein's target, activity, or association with other proteins.
Assume that investigators crossed a strain of flies carrying the dominant eye mutation Lobe on the second chromosome with a strain homozygous for the second chromosome recessive mutations smooth abdomen and straw body. The F1 Lobe females were then back crossed with homozygous smooth abdomen, straw body males, and the following phenotypes were observed. Smooth abdomen, straw body 820 Lobe 780 Smooth abdomen, Lobe 39 Straw body 54 Wild type 4 Smooth abdomen 148 Lobe, straw body 152 Lobe, straw body, smooth abdomen 3 Give the gene order and map units between these three loci
Lobe is in the middle Smooth abdomen-----5mu---lobe------15.35mu-------------------straw body
We have looked at the cloning experiments involved in producing Snuppy. After Snuppy was born, it was critical to show that Snuppy was indeed a clone of the donor Afghan hound. Describe the specific technique that was used and how the results demonstrated that Snuppy was in fact a clone of the donor Afghan hound.
Microsatellite analysis was used to show that Snuppy was a clone. Microsatellite loci are highly variable loci that contain a large number of DNA repeats (eg. 2, 3, or 4 nucleotides in length) at the population level. However, an individual can only have 2 of these alleles at any one microsatellite locus. By comparing the alleles that Snuppy had at 8 different microsatellite loci with those allele that the donor afghan hound and the surrogate mother had, it was shown that Snuppy had exactly all of the same alleles as the afghan hound, providing that Snuppy was a clone of the donor afghan
What is the difference between a missense mutation and nonsense mutation?
Missense mutations alter the coding sequence so that one amino acid is substituted for another. Nonsense mutations change a codon originally specifying an amino acid into a translation termination codon.
A coworker in your lab discovered a strain of E. coli that has nonfunctional RNA polymerase. He felt sorry for the suffering E. coli and decide to add an RNA polymerase enzyme and gene from Drosophila to this mutant to survive. You think that this is a foolish idea that will not work. Put together an argument as to why the addition of a Drosophila RNA polymerase could not possibly allow this mustant E. coli to survive.
Prokaryotic and eukaryotic RNA polymerases are different. The Drosophila RNA polymerase will not be able to find the E. coli promoters and thus not be able to transcribe any of the E. coli genes. Alt. answer: change it up by having a be a strain of yeast and complementing with the Drosophila polymerase III enzyme and asking why it doesn't work.
Describe the function of promoters in eukaryotes. Where are they usually located, relative to the corresponding gen? What two sequence elements do they normally possess?
Promoter regions are necessary for the initiation of transcription. Promoters that interact with RNA pol II are usually located within 100 bp upstream of a gene and usually contain TATA box (-26 to -30) and a CAAT box (-70 to -80)
Define RNA silencing (or interference). Explain how siRNAs arise and how they potentially affect gene expression. How are siRNAs different from the antisense RNA mechanisms?
RNA silencing, or RNA interference, occurs when double-stranded RNA molecules are cleaved and processed to produce small single-stranded interfering RNAs (siRNAs). These siRNAs bind to complementary sequences in mRNA molecules, stimulating cleavage and degradation of the mRNA. The siRNAs may also stimulate DNA methylation at DNA sequences complementary to the siRNAs. The paired mRNA-siRNA attracts a protein-RNA complex that cleaves the mRNA in an area bound by the siRNA. Following the initial cleavage, the mRNA is further degraded. The cleavage and subsequent degradation of the mRNA make it unavailable for translation. DNA methylation in the nucleus stimulated by siRNAs also affects transcription. Antisense RNA binds to mRNAs also, but physically interferes with transLATION.
Briefly describe two major differences between RNA and DNA at the level of the nucleotide
Ribose in RNA, deoxyribose in DNA Uracil in RNA, thymine in DNA
Albinism is a recessive condition resulting from the inability to produce the dark pigmentation in skin and hair. A man and a woman with normal skin pigmentation have two children. The man has one albino parent and the woman has parents with normal pigmentation but an albino brother. What is the probability that at least one of the children is albino? What is the probability that both children are albino?
Since one of the man's parents is albino, he must be a carrier (Aa) of the recessive allele. [ Probability = 1 ] The woman has an albino brother which means both of her parents are carriers; however, the woman who is not albino could have either AA or Aa as the genotype, aa is excluded because she is not albino. [ Probability = ⅓ or ⅔ ] . Case 1- The mother is Aa. The chance of having one affected child = ¼. The chance of having a non-affected child =¾. (¼)(¾)(2) = 6/16 (Must multiple by two because it could happen in either order). Must add the probability of having two albino = ¼ x ¼ = 1/16 + 6/16 = 7/16. (⅔)(7/16) =29.2% of one affected child. Both albino = (¼)(¼)(⅔) =4.2% Case 2- The woman is AA and the man is Aa. One albino child = 0
What DNA sequence occurs at the end of the Tetrahymena chromosome? Give both the sequence and the name of the structure. How does this sequence affect the conclusion of chromosome replication?
Telomeres terminate in a 5'-TTGGGG-3' sequence, and telomerase is capable of adding repeats to the ends, thus allowing the completion of replication without leaving a gap and shortening the chromosome following each replication.
The height of a type of bean plants is determined by five unlinked genes called A, B, C, D, and E. Each gene has two alleles: additive (uppercase letter) and nonadditive (lowercase letter). The shortest plants are 130 cm. The tallest plants are 220 cm. Estimate how many centimeters each allele contributes to the height difference of 90 cm.
The difference between the two heights is 90 cm. There are 10 alleles total (two each for five different genes). If each additive allele contributes equally to increasing height from a baseline of 130 cm, the contribution of each is 9 cm.
Nutritional mutants in Neurospora can be "cured" by treating the medium with substance in the defected metabolic pathway. What determines whether the mutant strain (auxotroph) is "cured" by a particular substance?
The mutant strain will be "cured" if the substance added occurs after the metabolic block in the biochemical pathway. This allows the mutant to effectively bypass the required gene product that is defective/mutant in the strain.
What is semi conservative replication?
The original two strands of the double helix serve as a template for new strands of DNA. When replication is complete, two double stranded DNA molecules will be present. Each will consist of one original template and one newly synthesized strand that is complementary to the template
Describe how the Sigma subunit of E.coli RNA polymerase participates in transcription.
The sigma subunit may give specificity to the RNA polymerase and play a role in regulatory function. It may be involved in the recognition of initiation sites and promoters
What is the spliceosome?
The spliceosome is the RNA-protein complex that is responsible for intron-exon splicing in eukaryotes. Following the GU-AG rule, introns are excised and removed from mRNA and the exons are joined to form a mature mRNA molecule ready for translation. The spliceosome is made of five small nuclear ribonucleoproteins (snRNPs) which consists of proteins and one of five snRNAs (U1, U2, U4, U5 and U6) which together with over 100 proteins form the large biological machine used for splicing.
How did the work of Hershey and Chase contribute to the model of DNA as the genetic material?
The work showed that (phage) DNA, and not protein, entered the cell in their experiments and that only DNA was passed on to progeny phages. Also OK: showed that DNA, and not protein, is the genetic material in phage.
What must be true for a population to be in Hardy-Weinberg equilibrium?
There must be random mating in the population; there must be an infinite population size; and there must be no evolution occurring (no natural selection, no genetic drift, no migration and no mutation).
An hh Bombay individual is transfused with type O blood. What will the effect be and why?
This blood will coagulate and cause a problem due to antibodies in the bombay individual to type O blood because the Bombay individuals lack the H substance, which in effect is type O
According to Hardy-Weinberg, if we know the frequency of each allele in the population, what can we predict?
We can predict what genotypes and phenotypes we should see in the population.
Regarding the tryptophan operon, trpR- maps a considerable distance from the structural genes. The mutation either inhibits the interaction with tryptophan or inhibits repressor formation entirely. In the presence of tryptophan in the medium, would you expect the tryptophan operon to be transcriptionally active in this mutant? Explain.
With either of the two scenarios mentioned in the problem, the absence of repressor function in a repressible system means that there would be no repression of the operon. The operon would be transcriptionally active.
Is it possible that the characteristic in the pedigree below could be X-linked dominant? If so, what are the genotypes of each individual (use alleles B and b)? If not, explain why not, giving specific genotypes.
X-linked recessive is possible if I-1 is XaY; I-2 is XAXa; II-1 is XAY; and II-2 is XaXa
What are zinc fingers, and why are they frequently encountered in descriptions of genetic regulation in eukaryotes?
Zinc fingers consist of amino acid sequences containing two cysteine and two histidine residues at repeating intervals. Interspersed cysteine and histidine residues covalently bind zinc atoms, folding the amino acids into loops (zinc fingers). They are one of the major groups of eukaryotic transcription factors. They were originally discovered in the Xenopus transcription factors TFIIA., and this structural motif has been identified in a variety of significant regulatory circumstances, including proto-oncogenes and developmental control genes in Drosophila.
The genetic frequencies of two separate populations are: AA Aa aa Population 1 .36 .48 .16 Population 2 .55 .10 .35 a) What are the genotypic frequencies of the two populations? b) What are the allele frequencies? c) Are the populations in Hardy-Weinberg equilibrium?
a) Expected for population 1: f(AA) = 0.36; f(Aa) = 0.48; f(aa) = 0.16 Expected for population 2: same b) Pop 1: f(A) = 0.6 = p f(a) = 1−p =0.4 = q Pop 2 : f (A) = 0.6 f(a) = 0.4 c) Population 1 is in Hardy-Weinberg equilibrium but population 2 is not.
A new kind of tulip is produced that develops only purple or pink flowers. Assume that flower color is controlled by a single-gene locus, and that the purple allele (C) is dominant to the pink allele (c). A random sample of 1000 tulips from a large cultivated field yields 847 purple flowers, and 153 pink flowers. a. Determine the frequency of the purple and pink alleles in this field population. b. Estimate the proportion of all purple flowering plants that are heterozygotes and homozygotes.
a. Assuming the population is in H-W equilibrium, let p = the dominant purple allele (C), and q = the recessive allele (c). Applying the H-W equation, the frequency of the pink allele = q^2 = 153/1000 = 0.153; and q = (0.153)^1/2 = 0.39. Because p + q = 1, p = 1 - q = 0.61. b. If the population is in H-W equilibrium, p^2 + 2pq + q^2 = 1. For the heterozygotes, 2pq = 2(0.61)(0.39) = 0.476. Therefore, 47.6%, or (0.476)(1000) = 476 of all the purple flowered plants in this population are expected to be heterozygotes (Cc), and consequently, (p^2)(1000) = (0.61)^2 (1000) = 371 plants are expected to be homozygous dominants (CC)
In snapdragons, the allele for red flowers is incompletely dominant over the allele for white flowers, and thus heterozygotes have pink flowers. What ratios of snapdragon flower colors would you expect to see among progeny generated from the following crosses? a. red x white b. red x pink c. white x pink d. white x white e. pink x pink f. red x red
a. all pink b. 1/2 red, 1/2 pink c. 1/2 pink, 1/2 white d. all white e. 1/4 red, 1/2 pink, 1/4 white f. all red
How are miRNAs produced? How do miRNAs function to affect production of proteins? Provide sufficient detail in your answer for full credit.
miRNAs are small RNA molecules transcribed from within an organism's genome. They are further processed after transcription by Dicer protein into small dsRNA molecules. These small ds molecules are targeted into RISC proteins where they are unwound into single stranded RNAs. These ss RNAs are then able to inhibit translation from mRNAs in a number of ways including inhibition of translation, targeting mRNAs for degradation, or sequestration of mRNAs.
The white-eye gene in Drosophila is recessive and sex linked. Assume that a white-eyed female is mated to a wild-type male. What would be the phenotypes of the offspring? Explain your answer
wild type females and white eyed males Females receive 2 copies of X chrom, 1 from white-eyed mom and 1 from wild type dad. White eyes are recessive, so the trait is masked. Males receive Y chrom from dad and Xrecessive from mom, so their white-eyed phenotype is shown.
