Genetics I Study Guide Exam 5
99. How do you read the DNA sequence after performing the chain termination sequencing in a single tube (using fluorescent dyes)? Are the peaks the sequence of the original DNA strand or its complementary strand sequence?
-all added to one tube, to which are added all four ddNTPs -each ddNTP is labeled with a differently colored fluorescent dye -mixture loaded into one lane -gel is scanned with a laser to fluoresce the dyes, and the fluorescence pattern (series of colored peaks) -read by a sequence machine -each peak represents one deoxyribonucleotide in the sequence -original DNA sequence
36. What are the three general steps of DNA repair?
1. Excision of the defective nucleotide(s) from one strand of the duplex -Endonuclease -DNA Polymerase I 2. Replacement of the missing nucelotide(s) -DNA Polymerase I 3. Ligation of the newly inserted nucleotide(s) to the remainder of the strand -DNA Ligase (phosphoester bond)
Shotgun Approach
1. with the use of one of a variety of more than 100 commonly used restriction endonucleases on a genome, specific DNA fragments can be generated. 2. with the use of sanitation, a genomic library of fragmented genomic DNA can be constructed. the DNA fragments are then cloned, and clones from the genomic library are elected at random and individually sequenced. 3. with the use of computer software, a final base sequence of all the clones from the genomic library is obtained by searching for overlapping base sequences among the clones
54. How do you determine the number of genes that interact to control a particular quantitative trait (aka what is the formula used in quantitative traits)? What does the letter "n" represent in the formula? Do you set the formula to equal the number of genotypes or phenotypes present in the population in order to solve for "n"?
2n + 1 = the number of phenotypes in the population n = the number of gene pairs interacting to influence the trait/final phenotype if you want to find the number of genes per trait: (#phenotypes - 1)/2 = number of gene pairs
96. Chain termination sequencing can use radioactive labeling with four different tubes and four different lanes on the gel OR it can be done using one tube and one lane on the electrophoretic gel. How is it possible to use only one tube and lane? What are the ddNTPs labeled with to make this possible?
4 Tubes, 4 Lanes DNA fragments are generated through restriction endonuclease digestion. Those fragments generated by different restriction enzymes are kept isolated from eachother. a. preparation of homogenous single strand of DNA b. label 5' end of ss DNA with 32P (radioactive label) c. divide DNA into 4 separate tubes d. cleavate of specific nucleotides in each one of the four tubes with either A, G, C, or T reagent (restriction endonuclease digestion) to generate short fragments used to sequence DNA e. sequential placement of DNA samples containg the fragments generated by A, G, C, or T digestion into wells at top (cathode end) of four separate adjacent lanes of gel -typical electrophoresis gel -each lane has ddGTP, ddATP, ddCTP, ddTTP -read the gel from bottom to top 1 Tube, 1 Lane -all added to one tube, to which are added all four ddNTPs -each ddNTP is labeled with a differently colored fluorescent dye -mixture loaded into one lane -gel is scanned with a laser to fluoresce the dyes, and the fluorescence pattern (series of colored peaks) -read by a sequence machine -each peak represents one deoxyribonucleotide in the sequence
8. What is the maximum percentage of crossing over between two genes (aka what is the maximum amount of recombination)?
49.9% (asymptotic curve above 20% recombination) never reaches 50% because then you'd be at Independent Assortment (no linkage, separate chromosomes) OR the genes would be on the very opposite tips of the chromosomes (telomeric) WHY? when the genes are further apart, a double crossover can occur -> reversion back to parental type: AB → AB → AB ab → ba → ab
76. In order for a DNA fragment to be inserted into a specific vector, should both the DNA and the vector be cleaved with the same restriction endonuclease? Why or why not?
>A heterogenous group of DNA segments inserted into a plasmid (vector; ex. pUC18) using EcoRI (makes sticky ends) and DNA ligase. >A vector joined to a desired DNA fragment is a recombinant DNA molecule. >Plasmid and DNA fragment must be exposed to the same restriction enzyme. >the fragmented DNA and vector must be cleaved with the same restriction endonuclease so that they possess the same available sticky ends
93. Describe the restriction mapping technique. What kinds of enzymes are used? How many tubes will you need? Why?
>DNA sequencing can be accomplished through restriction mapping by multiple or partial endonuclease digestion >Types of Enzymes Used: -EcoRI -HindIII -Bg1II -BstEII -EcoRV (restriction enzyme aka endonuclease) >Restriction maps are created by analyzing the number and length of the DNA fragments produced and piecing them together to construct a complete model >DNA fragments are separated by electrophoresis and mapping by partial endonuclease digestion specifically involves with use of a 32P radioactive marker 1. The first step following the completion of electrophoresis is to add up the sizes of the fragments in each lane. 2. The sum of the individual fragments should equal the size of the original fragment, and each digest's fragments should also sum up to be the same size as each other. # of test tubes = 2n + 1 n= number of enzymes being used ex. 3 enzymes being tested (Bg1II, BstEII, EcoRV) = 2(3)+1 = 7 test tubes Why? you want to test each enzyme individually and in combination with another enzyme + 1 for the marker lane (Lambda x HindIII) (not sure if +1 is all restricting mapping or just some?)
68. In a Chi-Square goodness of fit test evaluating Hardy-Weinberg Equilibrium/Law (aka that the allele frequencies do not change over the generations) what is the null hypothesis and the alternative hypothesis? What degree of freedom will you use in this particular test? What is the Chi-Square value in the table at that degree of freedom and at P=0.05?
>If x2 < x2 at 0.05 (3.841) with 1 df, then accept Ho (null hypothesis) Null Hypothesis: genotypic and allelic frequencies are in equilibrium # < 3.841 otherwise, reject Ho. accept Ha (alternative hypothesis) Alternative Hypothesis: genotypic and allelic frequencies are NOT in equilibrium # > 3.841
69. If your calculated Chi-Square value is less than the table Chi-Square value, will you accept or reject the null hypothesis? If you accept the null hypothesis, what does that indicate in terms of Hardy-Weinberg Equilibrium/Law?
>If x2 < x2 at 0.05 (3.841) with 1 df, then accept Ho (null hypothesis) if it is LESS than 3.841 you ACCEPT the null hypothesis (genotypic and allelic frequencies are in equilibrium) This means that the population IS IN Hardy-Weinberg equilibrium: - Use when dominance is complete and when there are two phenotypes and three genotypes. -This law states that in large populations, there are the following conditions: A. Frequency of one or two alleles is equal to p^2 B. Frequency of the other alleles is equal to q^2 C. Sum of frequency p + q = 1. D. Mating is random
97. Why is only a small amount of ddNTPs added to the chain termination sequencing reaction? Describe the competitive exclusion process.
>the higher the concentration of the ddNTP in the reaction, the shorter the products will be, hence, you will get sequence CLOSER to your primer. >With lower concentrations of ddNTP, chain termination will be less likely, and you will get longer products (sequence further AWAY from the primer). >you want the resulting newly synthesized DNA chains will be a mixture of lengths< competitive exclusion: states that two species that compete for the exact same resources cannot stably coexist. -ddNTP wants to attach
13. Be able to place genes in order on a chromosome based on the number of testcross progeny. For instance, take genes A, B, and D. Perform two-factor crosses first involving genes A and B, then with genes B and D, and finally A and D. Examine the percentage cross-overs and determine the map unit distances between the genes.
A and D has 10% recombination, 10MU apart B and D has 10% recombination, 10 MU apart if A is 10MU from D and B is 10MU from D then A and B must be 20MU apart
61. List the formulas for determining genotypic frequencies and allelic frequencies.
A and a (allelic frequency) p= frequency of A Fr (A) = p = [2*(#AA) + (#Aa)]/2N q= frequency of a Fr (a) = q = [2*(#aa) + (#Aa)]/ 2N Sum of frequency p + q = 1 Offspring of three genotypes in a definite ratio will be in equilibrium in the next generation in the frequency of: p^2 + 2pq + q^2 = 1 p^2 = # of homozygous dominant individuals (AA) 2pq = # of heterozygous individuals (Aa) q^2 = # of homozygous recessive individuals (aa)
88. What kind of liquid needs to be pored over (and submerges) the gel during gel electrophoresis?
A buffer solution (more precisely, pH buffer or hydrogen ion buffer) is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. >Its pH changes very little when a small amount of strong acid or base is added to it.
34. Please describe what happens in deletions and insertions.
A deletion or insertion can be of any size. However, deletions or insertions involving one base pair are point mutations. These alterations may radically alter protein function, and may be considered frame shift mutations. Most large DNA insertions will stop gene expression
78. What is the polylinker region on a plasmid vector?
A multiple cloning site (MCS, or Polylinker region) is a DNA region within a Plasmid that contains multiple unique Restriction enzyme cut sites. >Plasmids are very useful in biotechnology and one key feature of their use is the multiple cloning site, which allows for foreign DNA to be inserted into the plasmid.
86. What is Real Time PCR?
A real-time polymerase chain reaction, also known as quantitative Polymerase Chain Reaction, is a laboratory technique of molecular biology based on the polymerase chain reaction. >It monitors the amplification of a targeted DNA molecule during the PCR, not at its end, as in conventional PCR.
79. Define the term "recombinant DNA."
A vector is a carrier DNA molecule that carries the DNA fragment of interest into the host cell, and when a vector is joined to a DNA fragment, the unit is referred to as a "recombinant DNA molecule"
39. How is depurination damage repaired (recall the three general steps of DNA repair)? Note the specific enzymes involved in each of the repair steps.
A. Excision of depurinated sugar by repair endonuclease B. Insertion of missing nucleotide by DNA polymerase I C. Phosphoester bind formation by DNA ligase
67. Understand how to calculate the expected numbers of individuals of each genotype in the current population using the formerly known allele frequencies and the current population size.
AA = p^2 #AA = p^2(N) Aa = 2pq #Aa = 2pq(N) aa = q^2 #aa = q^2(N)
14. As the distance between two genes increases, there is a tendency for the percent cross over to increase or decrease (circle one).
As the distance between two genes increases, there is a tendency for the percent cross over to increase. 10 m.u. apart = 10% recombination 20 m.u. apart = 20% recombination if two far apart, there will be double-cross over events (reversion back to parental phenotypes)
26. List examples of chemical mutagens.
Chemical mutagens can (1) penetrate cells and (2) alter the chemical structure of the DNA within the cells. i) Mustard gas ii) Formaldehyde iii) Benzene
d. Based on the somatic cell hybridization data in your class slides, which chromosome appears to code for the enzyme thymidine kinase?
Chromosome 17
Know how to use this information to determine the configuration of the F1 parent (aka if the F1 parent was cis or trans).
Cis- the two dominant alleles are on the same chromosme and the two recessive alleles are on the same chromosome -parental progeny matches parents phenotype Trans- the dominant and recessive alleles are swapped on the two chromosomes -parental progeny does NOT match parents phenotype -recombinant offspring match parental phenotype
1. What is the definition of a cellular clone? (You also learned about DNA clones).
Clone-all the individuals derived by nonsexual propagation from a single original parent. A clone is a group of identical cells that share a common ancestry, meaning they are derived from the same cell. Clonality implies the state of a cell or a substance being derived from one source or the other.
4. Define crossing-over. Recall that crossing-over occurs during Meiosis I. Does crossingover occur between sister or non-sister chromatids?
Crossing Over: the exchange of chromatin material between non-sister chromatids of homologous chromosomes
77. What enzyme forms the covalent linkage between the DNA fragment and the vector's DNA (such as a plasmid)? Hint: this enzyme forms the phophodiester bonds on the sugar phosphate backbone of DNA.
DNA Ligase
38. What occurs during deamination? What nucleotide bases are involved?
Deamination -cytosine, adenine, or guanine -of the 3, cytosine is most susceptivle to deamination, giving rise to uracil -like depurination, deamination is a hydrolytic reaction caused by random thermal collisons of a water molecule with the bond that links the amino group of the base to the pyrimidine or purine ring -the rate of damage to the human genome by this means is about 100 deanimations per day
37. What occurs during Depurination DNA damage? What nucleotide bases are involved? What bond is broken?
Depurination -loss of a purine base (adenine or guanine) -by spontaneous hydrolysis of the glycosidic bond that links it to deoxyribose
Genetic Drift
Differential contribution of genotypes (offspring) to the next generation due to random events. Populations usually small.
Who invented PCR and when?
Dr. Kary Mullis in 1983 Kary Banks Mullis (December 28, 1944 - August 7, 2019) was an American biochemist. In recognition of his invention of the polymerase chain reaction (PCR) technique, he shared the 1993 Nobel Prize in Chemistry with Michael Smith and was awarded the Japan Prize in the same year.
90. How are the bands on the gel visualized? What is ethidium bromide? How can you visualize bands on a gel that has been stained with ethidium bromide?
Ethidium bromide is an intercalating agent commonly used as a fluorescent tag How it it visualized? >It can be used in the gel mixture, the electrophoresis buffer, or to stain the gel after it is run. >Molecules of the dye adhere to DNA strands and fluoresce under UV light, showing you exactly where the bands are within the gel. BUT in a southern blott X-ray film is applied over the top of the filter to produce an autoradiogram that will allow only those bands that have hybridized with the probe to be visualized.
64. Know how to determine p and q given the numbers of homozygous recessive individuals present in a population. Understand that knowing the p and q allele frequencies allows you to calculate the percent or frequency of individuals of a particular genotype in the population.
Ex. AA = 21 Aa = 53 aa = 26 N = 100
89. Describe how gel electrophoresis works. Do smaller or larger DNA fragments move through the gel faster? What charge is DNA? So where would you place the cathode (negative charge) and the anode (positive charge) in relation to a gel with DNA samples placed in the wells?
Gel Electrophoresis 1. DNA fragments are generated through restriction endonuclease digestion. Those fragments generated by different restriction enzymes are kept isolated from eachother. a. preparation of homogenous single strand of DNA b. label 5' end of ss DNA with 32P (radioactive label) c. divide DNA into 4 separate tubes d. cleavate of specific nucleotides in each one of the four tubes with either A, G, C, or T reagent (restriction endonuclease digestion) to generate short fragments used to sequence DNA e. sequential placement of DNA samples containg the fragments generated by A, G, C, or T digestion into wells at top (cathode end) of four separate adjacent lanes of gel 2. Agarose (for separation of large fragments) or polyacrylamide (for separation of small fragments) gels are prepared and placed in a horizontal gel electrophoresis apparatus 3. the fragments produced by different restriction enzymes (different base sequence recognition sites) are loaded into separate lanes (columns) of gel, with the first lane being occupied by a radioactive size marker 4. once separated by size exclusion and electrical charge, fragment positions in each lane can be visualized and photographed with the use of an ethidium bromide label (shines under UV light) Smaller DNA fragments move through the gel faster What charge is DNA? the phosphate group on each DNA nucleotide is NEGATIVELY charged So where would you place the cathode (negative charge) and the anode (positive charge) in relation to a gel with DNA samples placed in the wells? Cathode (-): top of the well Anode (+): bottom of the well, DNA migrates toward positive charge
60. What is gene frequency within a population? How can gene frequency be modified in a population?
Gene Frequency: the relative abundance or relative rarity of a particular gene in a population as compared with its own alleles in a population. >Any gene frequency takes a range from 0(not existent) to 1(the only gene available). A. Gene frequency is determined by the mode of inheritance. B. The variance is due to the frequency of the genes. C. Factors that may modify the gene frequency. 1) Selection - artificial selection. 2) Natural selection - what goes on in nature. Those with more viability continue to reproduce.
3. Define linkage.
Gene Linkage: The association of genes that are physically located on the same chromosome. -Different alleles of different segregating genes that are present together on a particular chromosome in parents tend to remain together on that chromosome in the progeny. -chromosomes that belong to same homologous set have same sequence of genes, but may have different allelic forms of each of those genes (A or a) Locus: The location of a gene on a chromosome. Linkage Group: all of the genes on a single chromosome. >They are inherited as a group; that is, during cell division they act and move as a unit rather than independently. >Each linkage group corresponds to one of the pairs of homologous chromosomes in the genome of that species. Linkage group in one pair of homologs.
49. Have a general understanding of the immunology associated with blood types. Why can't you give someone with type A blood a blood transfusion using type B blood? What blood type is the universal donor? What blood type is the universal recipient?
Genes I^O (a) - does not produce antigen, allows A and B antibodies to be produced. I^A (A) - produces antigen A, inhibits production of antibody A. I^B (A^B) - produces antigen B, inhibits production of antibody B. Antigen - A substance present on the red blood cells. >Antigen A, antigen B >pegs on RBC Antibody - A substance present in the serum of the blood. >Antibody A, antibody B. Antiserum - A serum that contains a known antibody. >Antiserum A, antiserum B. **Antigen-antibody-reaction - When an antigen (Antigen A) and its corresponding antibody (Antibody A) are brought together. >Type A blood has A agglutinogens and therefore agglutinates with anti-A agglutinins. >Type B blood has B agglutinogens and agglutinates with anti-B serum. >Type AB blood has both A and B agglutinogens and agglutinates with both types of serum >Blood Type O: universal donor >Blood Type AB: universal recipient
Forces Affecting Allele Frequency
Genetic Drift Selection
62. Define the ideal of Hardy-Weinberg Law (equilibrium). What are the five assumptions that must be met in Hardy-Weinberg Law in order for allele frequencies in a population to remain constant over the generations?
Hardy-Weinberg Law - Use when dominance is complete and when there are two phenotypes and three genotypes. >This law states that in large populations, there are the following conditions: A. Frequency of one or two alleles is equal to p^2 . B. Frequency of the other alleles is equal to q^2 . C. Sum of frequency p + q = 1. D. Mating is random. >Offspring of three genotypes in a definite ratio will be in equilibrium in the next generation in the frequency of: p^2 + 2pq + q^2 = 1 >5 Assumptions: 1. No Selection (no difference in fitness) 2. Random Mating 3. No migration (in or out, no gene flow) 4. No mutation 5. No genetic drift (infinitely large population)
56. What is heritability? How do you calculate heritability? Distinguish between the unselected population mean, the selected population mean, and the new population mean. Recall that the h2 component of the equation is calculated in decimal form (i.e. 33% is 0.33) and the h2 value does NOT need to be squared. h2 is a representation of the value.
Heritability (h^2) - Degree to which a given trait is controlled by inheritance. h^2 = ∆G/Sd OR h^2 = R/S S = Sd = selection imposed on the trait (can be strong or weak, and is different between selected and unselected population means) S= x̄ reproducing population - x̄ unselected population S= ps-p ps= selected mean p= unselected population mean R = ∆G = response of a population (given by the new population mean after selection) R= x̄ new population - x̄ original population R= pn-p pn= new population mean p= unselected population mean Overall Formulas: R= h^2*S h^2= R/S h^2= (pn-p)/(ps-p)
28. Who in 1927 used x-rays to show that external factors could cause DNA mutations using Drosophila melanogaster?
Hermann J. Muller Muller carried out two experiments with varied doses of X-rays, the second of which used the crossing over suppressor stock ("ClB") he had found in 1919. A clear, quantitative connection between radiation and lethal mutations quickly emerged.
55. What is heterosis (aka hybrid vigor)? How do you calculate heterosis?
Heterosis - Superiority of heterozygous genotypes in comparison with corresponding homozygous genotypes in respect to one or more traits. Heterosis = [(Avg. of hybrid offspring - Avg. of crossed breeds)/ Avg. of crossed breeds] *100
5. Explain the Holliday Model of Crossing Over. Include the following enzymes in your explanation: a. Endonuclease, DNA binding and/or DNA unwinding proteins (aka gyrase and helicase), proteins such as recA, Exonuclease, DNA polymerase, and DNA ligase
Holliday Model of Crossing Over: -Two Factor Cross: just looking at the relative distance between two genes -cross over only occurs between alleles that are heterozygous (if a b crossed with a b, then the cross would achieve nothing, it would still be the parental type) -occurs between non-sister chromatids -form a recombinant a. Two homologous DNA molecules line up (e.g., two nonsister chromatids line up during meiosis). b. Endonuclease creates cuts/nicks in one strand of both DNAs. c. DNA binding and/or DNA unwinding proteins (aka gyrase and helicase) unwind the DNA from the nicks d. Proteins like recA (recombinantA) cause the cut strands to cross and join homologous strands, forming the Holliday structure (or Holliday junction). -rebinding event -Heteroduplex region is formed by branch migration. e. Exonuclease, DNA ligase, and DNA Polymerase close the nicks by forming new hydrogen bonds into the opposite homolog -Chiasma: the X shaped region f. Rotational event allows top homolog to bend. The bottom homolog bends AND rotates 180degrees AB → AB ab → ba g/h. Endonuclease snaps the rotated chormosomes so now A pairs with b and B pairs with a -this is a transition from parental to recombinant form i. Exonuclease, DNA ligase, and DNA Polymerase form new phosphodiester bonds between the backbones and hydrogen bonds between the nucleotides j. final form of recombinant DNA
24. List the three examples of ionizing radiation that could cause mutations in DNA.
Ionizing radiation: short wavelength and high energy i) x-rays ii) alpha (α), beta (β), gamma (γ) radiation α particles = 2 protons and 2 neutrons from nuclei -Ra (radium) (workers licking brushes used in watch dial manufacturing - radium poisoning). β particles = emission of electrons -radioisotopes: 32P, 3H, 35S, 14C, 35Ca γ particles = emission of high energy protons -radioisotopes: 125I, 22Na iii) Cosmic rays Speical Notes: >Dosage of ionizing radiation is cumulative. >Low intensity x long time (chronic dosage) = high intensity x short time (acute dosage).
20. Can mutations occur in any cell type?
May occur in any cell A) Somatic- affects individual (cancer) -not heritable (unless asexual reproduction) B) Germ- affects individual but mostly affects offspring -heritable
85. Who won the Nobel Prize in 1993 for the use of Taq Polymerase in PCR?
Michael Smith >The Nobel Prize in Chemistry 1993 was awarded "for contributions to the developments of methods within DNA-based chemistry" jointly with one half to Kary B. Mullis
47. When working with multiple alleles, what formula is used to determine the number of different genotypes possible? What does the letter "n" represent in the formula?
Multiple alleles (more than 2 alleles for a gene in a population) [n (n + 1)] / 2 = the number of genotypes in the population n = the number of alleles in the population for a given gene for rabbits: n = 4 alleles (4(4+1))/2 = (4*5)/2 = (20)/2 = 10 possible genotypes in the population
46. There are the multiple alleles (three or more allelic forms of a gene) present in the population. How many alleles are present per gene in a somatic cell of an individual organism in that population?
Multiple alleles - three or more contrasting genes affecting the expression (phenotypes) of one character (detail of structure) >>>however, only two of these genes may occur in a genotype (somatic cell) >>>and only one is transmitted in a gamete.
17. What is the term for "Sudden, heritable changes in genetic material and the processes by which these changes occur"
Mutation: Sudden, heritable changes in genetic material and the processes by which these changes occur. >Most mutations are lethal and recessive. >These changes are not explained by recombination, but by either change in: • chromosome number [ex., euploidy (diploid, triploid, tetraploid)] • aneuploidy (chromosome # is not an exact multiple of the monoploid; ex., trisomy 21) • chromosomal aberrations [ex., the addition or loss of chromosome segments (ex., deletions, duplications, inversions, translocations)] • changes in individual genes [ex., most common uses of mutation (ex., mutons, where there are point mutations or changes in single base pairs, and, therefore, genes; example of a spontaneous mutation)]
30. What is a point mutation?
Mutations involving changes in single base pairs -substitutions -deletions -insertions
51. Quantitative traits exhibit continuous variation (as compared to discrete variation which is a one-or-the-other situation such as "yes" or "no"). What shape does a graph have when the frequency (percentage) of individuals is plotted on the y axis and the quantitative traits (phenotypes) are plotted on the x axis?
Normal Distribution --> bell shaped curve
53. What is another term for multiple genes working in conjunction to influence a single trait?
Polygene Concept or Complex Trait
82. What is the purpose of PCR (Polymerase Chain Reaction)? What happens to the DNA during the PCR reaction? How is a specific segment of DNA amplified?
Polymerase Chain Reaction: cloning WITHOUT the use of a host cell Step 1: The PCR Reaction (~4-5 min): i. Denaturation: The DNA to be amplified is denatured into single strands. This involves heating at 90 - 95°C. ii. Annealing: Temperature is lowered to between 50 and 70°C. This allows DNA primers to bind to denatured (single strands of) DNA. >DNA primers (15 - 30 nucleotides long; synthetic oligonucleotides) bind to sequences that flank the target segment. iii. Extension: Heat-stable DNA Pol (Taq) synthesizes daughter strands complementary to target sequences from primers at 70 to 75°C. Taq adds nucleotides 5' 3'. Step 2: Doubling of number of DNA strands after each full cycle. >25-30 cycles (~3 hours) increases DNA by 1 x 10^6 Step 3: The amplified DNA is recovered: >exposed to a variety of restriction endonucleases for multiple heterogenous cleaving >its sequence analyzed by agarose or polyacrylamide gel electrophoresis (Southern Blotting).
59. Define population genetics.
Population Genetics: dealing the with genetics of individuals that inhabit a particular area
58. Give the definition for a population.
Population: the total of all individuals in a breed or species or as those individuals that inhabit a particular area
43. How specifically does UV light affect/damage DNA? How is this DNA damage repaired?
Pyrimidine Dimer Formation -UV light -formation of a covalent bond between two adjacent pyrimidine bases, usually two thymines Removal -similar mechanism to the first two, except a UV-specific endonuclease is involved in nicking the defective region near the dimer The pathway, using multiple enzymes, which repairs the UV-damage in healthy cells is called nucleotide excision repair.
50. What are quantitative traits? List a few examples of quantitative traits.
Quantitative Traits >may be governed by many genes (perhaps 10-100 or more) >each contributing such a small amount to the phenotype that their individual effects cannot be detected by Mendelian methods. >Genes of this nature are called polygenes. >Thus, more than one gene may contribute to a given trait. >This is where we get the polygene concept as defined at the back of your workbook Examples: >height >weight >life span >skin color
48. List the two examples of multiple alleles discussion in class.
Rabbit Fur Color: C, c^ch, c^h, c Blood Type in Humans: IO, IA, IB
40. How is deamination damage repaired? Hint: The first enzyme is different in deamination, but then the steps of repair are exactly the same as in depurination DNA repair.
Repair of deaminated DNA follows a similar course, except that deaminated bases must first be detected and removed 1. this is done by DNA Glycosidase, enzyme that recognize deaminated base and remove it from the DNA by cleaving the glycosidic bond between the base and the deoxyribose sugar 2. The sugar with the missing base is recognized by the same repair endonuclease enzyme that detects depurination damage. 3/4. DNA Polymerase I replaces, and DNA ligase seals
92. What information does restriction mapping and chain termination sequencing give us? Hint: it is in the name.
Restriction Mapping: a method used to map an unknown segment of DNA by breaking it into pieces and then identifying the locations of the breakpoints. >This method relies upon the use of proteins called restriction enzymes, which can cut, or digest, DNA molecules at short, specific sequences called restriction sites. >the breakpoints are labeled using 32P markers Chain Termination Sequence: actual electrophoretic gel generated by chain termination sequencing shows the separation of DNA fragments in the four ddNTP (unlabeled) chain termination lanes >to obtain the 5' --> 3' base sequence of the DNA fragment, the gel is read from the bottom to the top, beginning with the lowest band in any lane >unlabeled by florescents, but still technically labeled by 32P in the gel OR >chain termination sequencing can be done using ddNTPs labeled with fluorescent dyes
70. If you wish to select for a particular trait, what three characteristics must the trait possess in the population?
Selection (S): differential contribution of offspring to the next generation due to differences in survivorship or fecundity (reproductive potential). a) artificial - imposed by man b) natural - interaction of environment and genotype. >For selection to occur, trait has to be: 1. Heritable 2. Must have genetic variation 3. Reproductive potential is greater than the carrying capacity - more offspring are produced than are able to live (difference of fitness)
a. What virus allows the human and mouse cells to fuse to create a hybrid cell? What is the term for the cells when the two cytoplasm fuse? What is the term for the hybrid cell when the human and mouse nuclei fuse?
Sendai Virus: forms little pegs on the cells, allows cells to stick together like Velcro (adhere to one another) Heterokaryon: when the cell cytoplasm fuse -first to form Hybrid Cell or Synkaryon: when the cell nuclei fuse -second to form
2. One example discussed in class was somatic cell hybridization fusing human and mouse cells.
Somatic cell hybrids are culture lines that contain the entire complement of the mouse genome and a few human chromosomes. >These culture lines are developed by mixing human and mouse cells in the presence of the Sendai virus. >The virus facilitates the fusing of the two cell types to form a hybrid cell
21. Describe the difference between spontaneous and induced mutations.
Spontaneous mutations • mutations that are not under the control of man • relatively infrequent • occur without a known cause • Due to: -biochemical mistakes during DNA replication -intrinsic errors in DNA repair (which may also be induced by environmental agents ex., lung cancer + smoking, skin cancer + uv irradiation) Induced mutations • mutations produced by man with a mutagen • Due to mutagens like: -ionizing radiation -uv light (solar radiation) -chemicals that react with DNA or RNA -viruses
84. What specific polymerase is commonly used for PCR reactions? Why is this polymerase used for this reaction?
Taq DNA Polymerase -used because it is heat-stable -synthesizes daughter strands complementary to target sequences from primers at 70 to 75°C -Taq adds nucleotides 5' 3'.
10. What is the map unit distance between two genes (aka what does the map unit distance indicate to a geneticist)?
The percent recombination between two markers indicates the map distance between them: 1% recombination = 1 map unit (m.u.). To determine the map distance between a pair of loci, count the number of SCO and DCO events, and use the following formula [the most common error is to neglect the DCO classes].
12. How do you figure out the map unit distance between two genes if the percentage linkage is over 20%?
The two parental types will be most abundant, the four single cross-over (SCO) recombinants will be next while the two double cross-over (DCO) recombinants will be least abundant. To determine the map distance between a pair of loci, count the number of SCO and DCO events, and use the following formula [the most common error is to neglect the DCO classes]. Map distance = % recombination = (# in SCO phenotypes + # in DCO phenotypes x 100) / (total # progeny) or follow the asymptotic curve
100. List all of the DNA technologies we discussed that used 32P (radioactive)?
Two screening processes: a) Recombinants (with foreign gene of interest) formed from these are screened by replica plating and autoradiography (32P - cDNA). -nitrocellulos -x-ray film Gel Electrophoresis -label 5' end of single-strand DNA with 32P (radioactive label) -Southern Blotting -Chain termination sequencing using ddNTPs labeled with 32P -restriction mapping using 32P marker
81. Not all host cells will take up the recombinant DNA, so we have to select or screen for cells that have taken up the recombinant DNA (because we aren't interested in host cells that don't contain the DNA of interest). Describe the techniques used to screen if a host cell has taken up your recombinant DNA. Hint: think about antibiotic resistance, X gal media, and replica plating and autoradiography.
Two screening processes: a) Recombinants (with foreign gene of interest) formed from these are screened by replica plating and autoradiography (32P - cDNA). -nitrocellulos -x-ray film b) Bacteria containing recombinant molecules can be screened. DNA segment inserts disrupt lac Z gene in pUC18 causing blue to white color change of colonies grown on Xgal media. Other bacteria can also be excluded by use of ampicillin in media, as the pUC18 vector contains an ampicillin-resistance gene. >Colonies produced from cells containing a recombinant plasmid are white, >whereas colonies from cells containing a nonrecombinant plasmid are blue.
73. If you are using DNA of known character, you could create a cDNA library to enable you to study parts of the DNA of interest. cDNA is double stranded DNA made from single stranded mRNA of your DNA or gene(s) of interest. Describe the steps (and enzymes) involved in creating double stranded DNA from mRNA. What is unique about the enzyme reverse transcriptase? What enzyme cleaves that final hairpin loop?
Use DNA of Known Character 1. isolate and purify mRNA possessing a poly-A (polyadenylated) tail at its 3' end from a cell population 2. combine the polyadenylated mRNA with poly-dT primers, so that the primers bind with the poly-A tails of the mRNA 3. add reverse transcriptase and deoxyribonucleoside triphosphates, which will allow synthesis of a DNA strand (single-stranded cDNA) complementary to the mRNA in the 5'→3' direction away from the primer site. An mRNA-DNA double-stranded hybrid molecule is formed >what is unique about reverse transcriptase: transcribes single-stranded RNA into DNA. >This enzyme is able to synthesize a double helix DNA once the RNA has been reverse transcribed in a first step into a single-strand DNA. 4. use RNAse H to nick and digest the mRNA strand in various places. The remaining undigested RNA pieces will serve as primers for initiation of the synthetic action of DNA polymerase I. 5. use DNA polymerase I to synthesize a second DNA strand and to excise the remaining RNA primer pieces. cDNA (complementary DNA) with a hairpin loop on one end is then formed 6. use S1 nuclease to cleave the hairpin loop and to derive double-stranded cDNA, which can be used in the development of a cDNA library via cloning
b. Once the human and mouse cells are fused, the hybrid cells randomly shed (get rid of) human chromosomes. Geneticists can easily distinguish between the mouse and human chromosomes based on staining. Specific DNA markers can identify what chromosome has a specific sequence present. These markers are complementary to the DNA sequence and can bind to or "hybridize" to the DNA and be recognized such as with specific staining or fluorescence. Based on the cell lines and the media used, this information can be used to determine where certain genes are located (on which human chromosome).
Use a HAT medium for incubation -selective for cells that are both TK+ positive AND HPRT+ positive -human cells are TK+ -mouse cells are HPRT+ -if the synkaryon is formed, the cell will be positive for both >cells are incubated for ~30 generations Clone A: chrom 17, positive for TK+ Clone B: chrom 17 and 3, positive for TK+ Clone C: chrom 17, 3, and 20, positive for TK+ All clones have chromosome 17 in common and all clones are positive for TK+ → so that means that TK+ must be located on chromosome 17
75. The DNA pieces formed from the shotgun approach may be cloned. The DNA is inserted into a vector and placed into a host cell. Define vector and host cell. List at least one example of a vector. List an example of a prokaryotic and a eukaryotic host cell.
Vector: a DNA molecule used as a vehicle to artificially carry foreign genetic material into another cell, where it can be replicated and/or expressed (e.g., pUC18, plasmid, cosmid, Lambda phages) >A vector containing foreign DNA is termed recombinant DNA. >DNA that has been fragmented by a restriction endonuclease (EcoRI makes sticky ends) can be mixed and then ligated (DNA Ligase) with a vector >Recombinant DNA molecule transferred to a host cell (bacterium) Host Cell: A cell that harbors foreign molecules, viruses, or microorganisms. For example, a cell being host to a virus. >A cell that has been introduced with DNA (or RNA), such as a bacterial cell acting as a host cell for the DNA isolated from a bacteriophage >Prokaryotic: E. coli (bacterium) >Eukaryotic: Saccharomyces cerevisiae (yeast) >once inside the host cell, the recombinant vector (recombinant DNA molecule) can undergo replication to produce many copies of clones (up to 500) of the recombinant DNA molecule
27. What else (naturally) has the capability to cause DNA mutations? Hint: It is debatable whether these are considered living or not.
Viruses
66. Allele frequencies in a population can be compared between the generations by using the Chi-square goodness of fit test. What is the formula for the Chi-Square test?
X^2 = Σ(observed - expected)^2/ expected Σ= summation
45. A genetic disorder of DNA repair in which the body's normal ability to remove damage caused by ultraviolet light is deficient. This leads to multiple basaliomas and other skin malignancies at a young age. In severe cases, it is necessary to avoid sunlight. What is the name of this genetic disorder?
Xeroderma Pigmentosum, or XP • A genetic disorder of DNA repair in which the body's normal ability to remove damage caused by ultraviolet (UV) light is deficient. • This leads to multiple basaliomas and other skin malignancies at a young age. In severe cases, it is necessary to avoid sunlight. • Damage to DNA in epidermal cells occurs during exposure to UV light. • The absorption of the high energy light leads to the formation of pyrimidine dimers. • The pathway, using multiple enzymes, which repairs the UV-damage in healthy cells is called nucleotide excision repair. • Briefly, the damage is excised by exonucleases, then the gap is filled by DNA polymerase I and sealed by DNA ligase. • The most common defect in XP is a genetic defect whereby nucleotide excision repair enzymes are mutated, leading to less or no repair of UV-lesions. • Unrepaired damage can lead to mutations, altering the information of the DNA. • If mutations affect important genes, like tumour suppressor genes (e.g. p53) or proto-oncogenes, then this may lead to cancer. • Since in XP patients the frequencies of mutations is much elevated, these patients have a predisposition for cancer.
31. What is a silent mutation?
a change in the sequence of nucleotide bases which constitutes DNA, without a subsequent change in the amino acid or the function of the overall protein. >typically in the 3rd nucleotide (wobble/degeneracy) >Sometimes a single amino acid will change, but if it has the same properties as the amino acid it replaced, little to no change will happen
32. What is a mis-sense mutation?
a change in the third nucleotide is not deleterious (silent mutation) But a change in one of the first two nucleotides in the codon may cause what is known as a mis-sense mutation, which could be detrimental.
33. What is a non-sense mutation?
a one-base insertion that changes a codon to a stop codon is considered a nonsense mutation and leads to a truncated protein. >This could greatly decrease the activity of a protein, and could sometimes be lethal. >A suppressor mutation is an addition mutation following a deletion mutation, or a deletion mutation following an addition mutation.
71. Describe the two main purposes of DNA cloning.
a) Artificial (in vitro) production of commercially important gene products. b) Increasing amounts of DNA that can be used for determining the nucleotide sequence of the gene of interest. -Ex., PCR (polymerase chain reaction)
91. What are the steps of Southern Blotting?
a) Digestion with restriction endonuclease enzymes b) Electrophoresis c) Use of radioactive probe d) Autoradiography (x-ray film) a) Digestion with restriction endonuclease enzymes 1. DNA fragments are generated through restriction endonuclease digestion. Those fragments generated by different restriction enzymes are kept isolated from eachother. a. preparation of homogenous single strand of DNA b. label 5' end of ss DNA with 32P (radioactive label) c. divide DNA into 4 separate tubes d. cleavate of specific nucleotides in each one of the four tubes with either A, G, C, or T reagent (restriction endonuclease digestion) to generate short fragments used to sequence DNA e. sequential placement of DNA samples containg the fragments generated by A, G, C, or T digestion into wells at top (cathode end) of four separate adjacent lanes of gel b) Gel Electrophoresis 2. Agarose (for separation of large fragments) or polyacrylamide (for separation of small fragments) gels are prepared and placed in a horizontal gel electrophoresis apparatus 3. the fragments produced by different restriction enzymes (different base sequence recognition sites) are loaded into separate lanes (columns) of gel, with the first lane being occupied by a radioactive size marker 4. once separated by size exclusion and electrical charge, fragment positions in each lane can be visualized and photographed with the use of an ethidium bromide label 5. the gel is placed underneath a nitrocellulose binding filter and above a wick (sponge) partially immersed in a buffer solution. The upward movement of the buffer, via capillary action, transfers the DNA fragments from the gel onto the nitrocellulose filter 6. the double-stranded DNA fragments on the filter are denatured into single strands by treatment with a denaturation (alkaline) solution c) Use of radioactive probe 7. the filter is then placed in a heat sealed bag with a radioactively labeled single-stranded probe for a minimum of 6 hours at 37°C-42°C the probe will hybridize with the single-stranded fragments on the filter, if their base sequences are complimentary 8. the filter is washed to remove unbound probe, leaving only labeled double-stranded hybrid DNA on the filter d) Autoradiography (x-ray film) 9. the filter is finally dried and X-ray film is applied over the top of the filter to produce an autoradiogram that will allow only those bands that have hybridized with the probe to be visualized. 10. knowing the point at which fragments were cut (corresponding to their respective restriction enzyme lane) and relative positioning of the fragments (bands) to one another on the gel
72. Name the two means by which DNA is derived for cloning.
a) Use DNA of known character: • purified mRNA →single stranded cDNA (reverse transcriptase) • cDNA →double stranded DNA (DNA polymerase 1) • Formation of cDNA library. b) Shot-gun approach: • Use one of a variety of restriction endonucleases (ex. EcoR1) on a genome to generate specific DNA fragments. • shotgun method attaches fragments that match/overlap
6. You perform two-factor crosses between F1 individuals and test-cross parents. Suppose you obtain the genotypic ratios found below in a, b, and c in the offspring among your different crosses. Label the ratios as Independent Assortment, Complete Linkage, or Normal Linkage. a. 6:1:7:2 b. 1:1:1:1 c. 1:1
a. 6:1:7:2- normal linkage b. 1:1:1:1- Independent Assortment c. 1:1- complete linkage Independent Assortment: -No linkage, separate chromosomes -50% parental type progeny -50% recombinant progeny Complete Linkage: -Total linkage, no break between genes -genes are SOOO close together, that recombination is not possible -100% parental type progeny Normal Linkage: -There is some relative distance between genes, some crossing over occurs -dependent on how distant genes are -% parental progeny > % recombinant progeny
83. Name the three main steps in PCR (Polymerase Chain Reaction). This occurs in a machine called a thermal cycler. It takes about 3 hours to run through 25-30 cycles of these three steps: a. _____________ Occurs at 90-95ºC b. _____________ Occurs at 37-70ºC c. _____________ Occurs at 70-75ºC
a. Denaturation Occurs at 90-95ºC b. Annealing Occurs at 37-70ºC c. Extension Occurs at 70-75ºC
87. Name the two kinds of gels we discussed that are used in gel electrophoresis? Aka what are the gels made of? Hint: you make the gel almost exactly like you make Jello-only you don't have to refrigerate the gel-it solidifies at room temperature.
agarose or polyacrylamide gel electrophoresis (Southern Blotting) Agarose: polysaccharide, generally extracted from certain red seaweed. It is a linear polymer made up of the repeating unit of agarobiose, which is a disaccharide Polyacrylamide Gel: prepared by free radical polymerization of acrylamide and a comonomer crosslinker such as bis-acrylamide. Agarose gels can be used to resolve large fragments of DNA. Polyacrylamide gels are used to separate shorter nucleic acids, generally in the range of 1−1000 base pairs, based on the concentration used.
22. What is a mutagen (aka a mutagenic agent)?
an environmental agent that is capable of inducing a mutation
52. What happens to the graph as the number of additive genes (genes all interacting on the single trait) increases?
as the number of genes interactivity to influence trait increases ∝ the more perfect the curve is and the wider the curve
80. How can recombinant DNA be taken up by a host cell?
before a recombinant DNA molecule can be introduced into a host cell, the host cell must be heat shocked prior to transfer
44. Can DNA replication and transcription proceed if a pyrimidine dimer is formed?
both replication and transcription are blocked by such dimers (enzymes in these functions cannot cope with dimer structure)
15. Does crossing-over occur in male Drosophila melanogaster?
crossing over ONLY occurs in FEMALE drosophila lack of required proteins in the male drosophila before the meiosis process
95. Chain termination sequencing uses small amounts of dideoxyriboneucleotide triphosphate precursors (ddNTPs). Dideoxy means there are two hydroxyl groups (-OH) missing from the ribose sugar instead of the usual one in DNA (at carbon #2). At which carbon position (#) is the second hydroxyl group missing? Why would this stop/terminate DNA synthesis?
dideoxyriboneucleotide triphosphate precursors (ddNTPs) -missing an OH from the 2' AND 3' carbon -Without the 3' OH, no more nucleotides can be added -DNA polymerase falls off. -The resulting newly synthesized DNA chains will be a mixture of lengths, depending on how long the chain was when a ddNTP was randomly incorporated. -the triphosphate provides energy
65. Know how to calculate the probability of a gamete carrying a particular gene. Know how to calculate the probability of particular gametes fusing to form homozygous and heterozygous individuals in that population.
fr(A) = p fr(a) = q frequency of a gamete with a particular phenotype is either: p^2 (AA) pq (Aa) q^2 (aa) if two heterozygotes are mating it is 2pq because the chance of a heterozygous progeny is (2/4)
29. Low intensity x long time (chronic dosage) = ?
high intensity x short time (acute dosage).
Rules of Plant Height
homozygous recessive individual = 10 cm tall for every dominant allele you add to the genotype of an individual add 10 cm per each dom allele starting with a base of 10 cm
7. In a normal linkage situation, which testcross offspring are the in highest percentage: the parental or the recombinant types? Why? Know how to use this information to determine the configuration of the F1 parent (aka if the F1 parent was cis or trans).
in normal linkage, gametes or testcross progeny that are in the highest percentage are parental types or non-crossovers (N.C.O), whereas those in the lowest percentage are recombinant types or crossovers 0% (CL) < R < 50% (IA) 50% (IA) < P < 100% (CL) ex: R= 40%, P= 60% WHY?- the percentage of recombination is directly related to the distance in microunits between the genes -if genes A and D are 10 microunits apart, then they will have 10% recombinant progeny (up to 20%, then asymptotic curve) -the closer two genes are, the fewer recombinant progeny they can produce -if they are TOO far apart double cross over occurs, revert back to parental type Trans or Cis Parent?
c. In the example from class, what kind of mutant are the mouse cells (what gene)? What kind of mutant are the human cells? [Hint: a mutant cell is negative (or lacks) a certain gene.]
mutant cell- negative for a certain gene human cells are HPRT- mouse cells are TK-
74. What kinds of enzymes does the "shotgun approach" use? List an example of this kind of enzyme.
one of a variety of restriction endonucleases (ex. EcoRI; an enyzme isolated from E. coli, HindIII, BamHI, TaqI) -enzymes that locate a recognition sequence at which they cut both strands of double helical DNA into fragments called restriction fragments -these enzymes serve as natural defenses against invading viruses -bacterium protects its own DNA from a particular restriction enzyme by modifying (ex. methylation) the recognition sequence on its DNA specific for that enzyme
63. Hardy-Weinberg Law utilizes the two equations listed below. Please describe what p and q represent. What do p2, 2pq, and q2 represent? a. p + q = 1 b. p 2 + 2pq + q2 = 1
p + q = 1 p= frequency of dominant allele q= frequency of recessive allele p^2 + 2pq + q^2 = 1 p^2 = # of homozygous dominant individuals (AA) 2pq = # of heterozygous individuals (Aa) q^2 = # of homozygous recessive individuals (aa)
94. How do you read the DNA sequence on the gel after performing the restriction mapping technique? Which end of the DNA (5' or 3') is at the bottom of the gel? Do you know the first nucleotide using this technique?
read from bottom to top bottom is the least amount of base pairs from restriction site (top is farthest from restriction site) EcoRI cuts DNA at the sequence GTTAAC, so if you know where EcoRI is, you know that the first nucleotide there is a G DOESN'T MATTER
98. How do you read the DNA sequence on the gel after performing the chain termination sequencing using radioactive labeling (so you have four lanes on the gel)? Which end of the DNA (5' or 3') is at the bottom of the gel? Are you reading the sequence of your original DNA strand or its complementary strand off the gel?
read gel from bottom to the top the bottom of the gel is the 5' end you're reading the original DNA strand
35. Are silent mutations, mis-sense mutations, non-sense mutations, and deletions and insertions all also considered point mutations?
silent mutations, mis-sense mutations, and non-sense mutations are all considered point mutations insertions and deletions can be considered point mutations if it involves one base pair, but insertions and deletions can be any size
57. As selection occurs on a quantitative trait, will the curve become narrower or wider?
the wider the curve, the more loci affecting the trait, polygenic BUTTTTT as selection proceeds, curve gets narrower and narrower
25. What is an example of non-ionizing radiation that can cause mutations?
ultraviolet light
11. When does the percentage cross over equal the map unit distance?
up to 20%
16. Please explain the importance of a three factor cross. Consider double cross-over events.
very useful for genes that exceed 20 m.u. distance between them A third gene that maps between two other loci can be used to identify two-factor crosses that might otherwise go undetected due to the occurrence of double crossovers in addition, this allows one to order the three factors involved or part of a linkage group (whats on outside, whats on middle) It will also help correct the underestimation, at least in part, of the mapping distance between two factors which would have been estimated based on a two factor cross
41. Deamination and depurination events are considered hydrolytic reactions. What molecule causes the DNA damage?
water (H2O)
42. When DNA ligase repairs a phosphodiester bond in the sugar phosphate backbone of DNA, what molecule is produced?
water (H2O)
9. How do you calculate the percentage cross-over/recombination when given the numbers of each of the genotypes of the offspring resulting from a cross between an F1 parent and a testcross parent?
you take the total percentage of recombinant offspring (# of genotype/N) N= total # of offspring AD: 45% ad: 45% Ad: 5% aD: 5% 10% recombination
23. What is the minimal level of DNA base pair mistakes allowed naturally without causing problems associated with mutations?
• Mistakes in DNA nucleotide (base pair) selection are corrected to some extent by DNA polymerase activity • a minimal level of mistakes (1 x 10^-10 = errors/synthesized nucleotide) may still normally go unrepaired. • The level of this occurrence may be increased by environmental mutagenic agents.
19. Mutations are usually lethal and recessive. When could a mutation be a good thing?
• Mutations introduce variation (alleles) and, thus, help drive natural selection. • Mutations are the basic source of all genetic variation. • However, too many mutations would disrupt the normal transmission of genetic material from generation to generation.
18. We went over an example of a mutation involving chromosome 22 and chromosome 9 in humans. This mutation involved translocation (a type of aberration) where chromosome 22 becomes abnormally shortened which leads to CML (chronic myeloid leukemia). What is the name of the shortened chromosome 22 that causes this disease?
• Philadelphia chromosome (Ph chromosome) is an abnormality that causes chronic myeloid leukemia (CML) in humans. • The Ph chromosome is chromosome 22 that has become involved in a translocation (an exchange of material) with chromosome 9. • In this mutational process, chromosome 22 becomes abnormally shortened. • This translocation takes place in a single bone marrow cell, and through clonal expansion of this one mutant cell, gives rise to CML. Chronic myelogenous leukemia (CML) is an uncommon type of cancer of the bone marrow — the spongy tissue inside bones where blood cells are made. CML causes an increased number of white blood cells in the blood
