For each of questions, select and support the most appropriate response, and exp
ID: 102252 • Letter: F
Question
For each of questions, select and support the most appropriate response, and explain why each of the incorrect statements is eliminated. (GENETICS EXPERT)
1. Adeno-associated virus (AAV) can carry a human gene into bone marrow cells. A patient received this genetically modified bone marrow, which resulted in production of a required enzyme. This is an example of
a. protein therapy.
b. germline therapy
c. somatic gene therapy
d. retroviral gene therapy
e. in vivo gene therapy
2. A procedure that combines gametes in a culture dish, then eventually transfers the resulting embryo to the female gamete donor’s uterus is
a. IVF.
b. intrauterine insemination.
c. surrogate insemination.
d. GIFT.
e. ICSI.
3. Sequencing of the human genome can reveal
a. mutations that do not alter phenotype.
b. mutations that do not alter genotype.
c. which tissues express a gene.
d. how many genes a person has.
e. epigenetic effects.
4. An inherited mutant p53 allele
a. creates DNA replication errors.
b. causes a Mendelian cancer trait.
c. is an oncogene.
d. raises the risk of cancer.
e. binds to DNA to increase transcription.
5. DNA
a. is always interpreted using the same code, with minor exceptions.
b. incorporates any type of the five nitrogenous bases.
c. bases occur in random order.
d. joins bases to each other covalently.
e. is not the genetic material in bacteria.
6. Which of these factors does not influence the rate of mutation?
a. the presence of a repetitive sequence
b. the protein encoded by the gene
c. the presence of a palindrome
d. a gene’s length
e. the ability to repair DNA
7. Eugenics
a. depends on voluntary participation.
b. is successful at eliminating harmful recessive alleles from a population.
c. is a form of natural selection.
d. is intended to alleviate individual suffering.
e. may involve sterilization.
8. Analysis of which source of data does not contribute to tracing human and/or ancestral human migration patterns?
a. fossils
b. mitochondrial DNA
c. admixture info
d. chromosome banding
e. haplogroups
Explanation / Answer
1) The solution is Retroviral gene therapy.
Reason: First viruses to be used as vectors in gene therapy experiments were retroviruses. They belong to a class of viruses (RNA as genetic material ) which can create double stranded DNA copies with the enzyme reverse transcriptase. These copies of its genome can be integrated into the chromosome of host cell by another enzyme carried the virus called integrase. Now the host cell has been modified to contain a new gene. If such modified host cells divide later, their descendants will contain the new genes. Although retroviruses have been used in most gene therapy experiments so far, they present problems.One such problem is that integrase enzyme can insert genetic material of the virus into any arbitrary position in the genome of the host, which can lead to insertional mutagenesis (if insertion is in the middle of the gene) or uncontrolled cell division (if gene happens to be one regulating cell division) leading to cancer. This problem has recently begun to be addressed by utilizing zinc finger nuclease or by including certain sequences such as beta globin locus control region to direct the site of integration to specific chromosome.
Gene therapy trial using retroviral vector to treat X-linked severe combined immune deficiency represent the most successful application till date.
Also this has been tried to treat SCID due to ADA deficiency with relative success. As researchers have grown more confident, they have begun injecting altered retroviruses directly into tissues where the corrected genes are needed. For example- in cystic fibrosis (mutated gene impairs lung function), healthy genes are inserted directly to the lining of bronchial tube. Experimental animal studies are being conducted to establish the effect in muscular dystrophy.
The following are eliminated due to :
a) Protien Theory: Theory of protein folding, As a result of evolution, proteins have a rugged funnel-like landscape biased toward the native structure. Connecting theory and simulations of minimalist models with experiments has completely revolutionized our understanding of the underlying mechanisms that control protein folding.
b) Germ line gene therapy: where germ cells (sperm or egg) are modified by the introduction of functional genes, which are integrated into their genome. Therefore changes due to therapy would be heritable and would be passed on to later generation. Theoretically, this approach should be highly effective in counteracting genetic disease and hereditary disorders. But at present many jurisdictions, a variety of technical difficulties and ethical reasons make it unlikely that germ line therapy would be tried in human beings in near future.
c) Somatic gene therapy: where therapeutic genes are transferred into the somatic cells of a patient. Any modifications and effects will be restricted to the individual patient only and will not be inherited by the patients offspring or any later generation.
e) in vivo gene therapy: does not use cells from the patient’s body. Vectors with the normal gene are injected into patient’s blood stream to seek out and bind with target cell.
2) The solution is: a) IVF, the possible reason is: These reproductive cells could then be used to create fertilized embryos to be implanted into a woman's uterus.
The ones which are eliminated are:
b) Intrauterine insemination (IUI) is a fertility treatment that involves placing sperm inside a woman's uterus to facilitate fertilization. The goal of IUI is to increase the number of sperm that reach the fallopian tubes and subsequently increase the chance of fertilization
c) Gestational Surrogacy, by contrast, results from in vitro fertilization. A Gestational Surrogate is not the biological mother of the child as she does not provide the egg. Instead, the egg is provided by an egg donor or, by the Intended Mother. The egg is fertilized by the sperm of a Donor or the Intended Father through the process of in vitro fertilization, then grown into an embryo, and then implanted into the gestational surrogate.
d) Gamete intrafallopian transfer (GIFT) uses multiple eggs collected from the ovaries. The eggs are placed into a thin flexible tube (catheter) along with the sperm to be used. The gametes (both eggs and sperm) are then injected into the fallopian tubes using a surgical procedure called laparoscopy. The doctor will use general anesthesia.
e) Intracytoplasmic Sperm Injection (ICSI) is a specialised form of In Vitro Fertilisation (IVF) that is used for the treatment of severe cases of male-factor infertility. ICSI involves the injection of a singlesperm directly into a mature egg.
3) The correct answer is : a) mutations that do not alter phenotype- the possible reason is Phenotype is determined by an individual's genotype and expressed genes, random genetic variation, and environmental influences. Examples: Examples of an organism's phenotype include traits such as color, height, size, shape, and behavior.
The eliminated options are :
b) The genotype is the set of genes in our DNA which is responsible for a particular trait.
e) Epigenetics is the study of potentially heritable changes in gene expression (active versus inactive genes) that does not involve changes to the underlying DNA sequence — a change in phenotype without a change in genotype — which in turn affectshow cells read the genes.
4) Option c and d sound most appropriate :
c. is an oncogene.
d. raises the risk of cancer.
This is because:
Inactivation of the p53 tumor suppressor is a frequent event in tumorigenesis. In most cases, the p53 gene is mutated, giving rise to a stable mutant protein whose accumulation is regarded as a hallmark of cancer cells. Mutant p53 proteins not only lose their tumor suppressive activities but often gain additional oncogenic functions that endow cells with growth and survival advantages. Interestingly, mutations in the p53 gene were shown to occur at different phases of the multistep process of malignant transformation, thus contributing differentially to tumor initiation, promotion, aggressiveness, and metastasis. Here, the authors review the different studies on the involvement of p53 inactivation at various stages of tumorigenesis and highlight the specific contribution of p53 mutations at each phase of cancer progression.
5) Options a and d are correct.
Reason:
DNA is one of the nucleic acids, information-containing molecules in the cell (ribonucleic acid, or RNA, is the other nucleic acid). DNA is found in the nucleus of every human cell.Although it may look complicated, the DNA in a cell is really just a pattern made up of four different parts called nucleotides. Imagine a set of blocks that has only four shapes, or an alphabet that has only four letters. DNA is a long string of these blocks or letters. Each nucleotide consists of a sugar (deoxyribose) bound on one side to a phosphate group and bound on the other side to a nitrogenous base.
6) Option c and d.
Reason: The other three are dependent because :
The mutation rate is the frequency with which a gene changes from the wild type to a mutant. It is commonly expressed as the number of mutations per biological unit, which may mean per cell division, per gamete, or per round of replication.
The mutation frequency, however, is defined as the incidence of a specific type of mutation within a group of individual organisms, which is expressed as a percentage of the total.
7) Option b and c can be appropriate solutiions.
Reason: the science of improving a population by controlled breeding to increase the occurrence of desirable heritable characteristics.
8) Option b is correct.
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