A. Incorrect! All the cells have the same set of genes. (D)Because different types of cells have different types of transcriptional factors.

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1 Genetics - Problem Drill 21: Cytogenetics and Chromosomal Mutation No. 1 of Why do some cells express one set of genes while other cells express a different set of genes during development? (A) Because they have different gene compositions. (B) Because different types of cells have different type of extracellular signals. (C) Because different types of cells have different types of cellular determinants. (D) Because different types of cells have different types of transcriptional factors. (E) Because the master control gene can regulate all transcriptional activity. All the cells have the same set of genes. Extracellular signals can affect gene expression; it is differential gene expression. Cellular determinants determine the cell s fate; it occurs before differentiation. D. Correct! Transcription factors play key roles in differentiation. The master control gene can only regulate a subset of gene expression, not all. The key of the theory of differential gene expression is about transcription factors and their signal cascade. (D)Because different types of cells have different types of transcriptional factors.

2 No. 2 of People have been searching for the initial determinants ever since the Mosaic Theory was developed in 19 th century. What are the likely determinants? (A) Genes (B) Proteins (C) Small molecules out of cells (D) Small molecules in cells (E) RNA Genes do not split up and do not divide unevenly, as suggested by the Mosaic Theory. Proteins are possible candidates, but experiments do not support this. Determinants are inside the cell, not on the outside. Small molecules are not determinants. E. Correct! The final product is still protein, but RNA seems to be the molecule split unevenly and leading to determination. Mosaic Theory and Theory of Differential Gene Expression are the two key theories to understand cell fate and differentiation. (E) RNA

3 No. 3 of Multipotent stem cells can. (A) Differentiate into all types of tissues and organs. (B) Differentiate into a group of pluripotent stem cells. (C) Produce cells of unrelated families. (D) Produce cells of closely-related families. (E) Produce terminally-differentiated cells. This is totipotent, the embryonic stem cell. Multipotent stem cells are differentiated from pluripotent cells, not reverse. Multipotent stem cells produce cells of related cells. D. Correct! That is part of the definition of multipotent cells. Stem cells eventually all produce terminally-differentiated cells. Stem cells are classified as totipotent, pluripotent, multipotent and unipotent, depending on their potential to differentiate. (D)Produce cells of closely-related families.

4 No. 4 of All of the following observations support that the nucleus can be re-programmed except for. (A) Cell fusion experiments (B) Nuclear transplantation experiments (C) Trans-differentiation (D) De-differentiation (E) Cell polarity Cell fusion experiments revealed that some activity in cytosol can reprogram the nucleus. This is the strongest evidence that a cell nucleus can be re-programmed. This is another piece of evidence that a nucleus can be reprogrammed. When the nuclear reprogramming occurs, one of the effects is de-differentiation, which reverses the process. E. Correct! Cell polarity can be used to explain the Mosaic Theory because the determinants are not evenly distributed within a cell, but it is not evidence for nucleus reprogramming. Nuclear reprogramming is still not fully understood, but apparently it is a coordinated result from cytosol factors and DNA structure changes. (E)Cell polarity

5 No. 5 of Antibody is encoded by a limited number of genes, but antibodies are known for their diversity; this is because. (A) Mutation occurs within those genes. (B) B-cells respond to stimuli in various ways. (C) T-cells respond to stimuli in various ways. (D) The lymphocytes differentiate into different types of immune cells. (E) DNA recombinate during B-cell maturation. Mutation may occur within these cells, but frequency can be very low and cannot account for the large possibility of antibody production. B-cells respond to stimuli mostly in a very similar way. T-cells do not produce antibodies, so it is not related. The lymphocytes differentiate into different types of immune cells, including T-cell, B-cell, Natural killer cell, and macrophage, etc. However, this is not the reason for antibody diversity. E. Correct! DNA recombination accounts for antibody diversity, and it occurs during B-cell maturation; therefore, there are a huge number of B-cells with different antibody specificities. B-cell maturation is important in antibody diversity. (E)DNA recombinate during B-cell maturation.

6 No. 6 of Which of the following statements about the structure of a chromosome is true? (A) The centromere is towards the middle of the chromosome. (B) The long arm of a chromosome is known as the p arm. (C) A telomere is DNA on both sides of the centromere. (D) A chromosome has 4 identical arms connected to the centromere. (E) A chromosome has 4 arms all the same length, with different DNA in each. A. Correct! The centromere is towards the middle of the chromosome. The p arm is the short arm of a chromosome. A telomere is DNA located on the ends of chromosomes, away from the centromere. A chromosome typically has 2 p arms and 2 q arms connected at the centromere. A chromosome typically has 2 p arms and 2 q arms connected at the centromere. Chromatin is the general structure of any chromosome; the basic units are nucleosomes. It also refers to the extended form of a chromosome, e.g. in interphase. A chromosome is the unit of inheritance with the basic structure of arms, centromere and two telomers. Chromosomes are in the nucleus of each cell. Chromosomes consist of DNA coiled many times around histones. The metaphase chromosome is primarily used in cytogenetics studies because they condense and form the characteristic shape shown in this image. The short arm is labelled the p arm, the long q. Centromere location gives the chromosome its characteristic shape. (A)The centromere is towards the middle of the chromosome.

7 No. 7 of Which of the following statements about FISH is correct? (A) Fluorescence in situ hybridization is a technique used to identify a gene or portion of a chromosome. (B) FISH is a technique that involves spreading out metaphase chromosomes and visualizing them under the microscope; no dye or probe is needed. (C) The FISH technique is used to visualize the overall structure of the chromosomes; an amplification of part or all of a chromosome would not be detected. (D) Cells that are not in the cell cycle are used so the DNA is spread out and easier to visualize. (E) Telophase chromosomes are the best to use for the FISH technique. A. Correct! Fluorescence in situ hybridization is a technique used to identify a gene or portion of a chromosome. A fluorescent probe is used to target the gene or DNA sequence of interest. FISH can be used to detect amplifications. Cells are harvested when in Metaphase and are fixed. Cells are harvested when in Metaphase and are fixed. FISH: fluorescence in situ hybridization. DNA that has been tagged with a fluorescent probe is hybridized to a chromosome. It is used to locate or amplify a gene on a chromosome. FISH uses fluorescent tags to label cellular DNA to visualize a chromosome. Procedure: 1. Harvest and fix metaphase chromosomes. 2. Hybridize to fluorescence-labeled DNA probes. 3. Visualize chromosomes under a fluorescence microscope. (A)Fluorescence in situ hybridization is a technique used to identify a gene or portion of a chromosome.

8 No. 8 of Chromosome mutations. (A) Come in two main types, a change in chromosome number and color. (B) Come in two main types, a change in number and a change in structure. (C) Can be caused by certain chemicals but not due to radiation because of their structure. (D) Are always caused by a mutagen. (E) Such as Down s syndrome include only a total loss of a certain chromosome. Chromosome mutations include changes in the number of chromosomes, as well as the structure. B. Correct! Chromosome mutations include changes in the number of chromosomes, as well as the structure. UV radiation can cause breaks and damage to chromosomes. There can be spontaneous chromosomal mutations. Down s Syndrome is characterized by an extra copy of chromosome # 21 - for a total of three. There are two types of chromosomal mutations important in cytogenetics. These are changes in chromosome number and chromosome structure. Down s syndrome is an example of a change in chromosome number; it has 3 copies of chromosome #21. The causes of these mutations can be spontaneous or induced by a mutagen. UV radiation can cause chromosome breaks and mutations. (B)Come in two main types, a change in number and a change in structure.

9 No. 9 of Which of the following statements about aneuploidy is correct? (A) Aneuploidy is only the deletion of all or part of a chromosome. (B) Aneuploidy is the deletion or amplification of the entire set of chromosomes. (C) The cause of aneuploidy, in general, is when none of the chromosomes segregate to the daughter cell. (D) One mechanism of aneuploidy is the presence of a kinetochore. (E) Down s syndrome in a male is identified as 47 XY, 2N+1. Aneuploidy is defined as the addition or deletion of all or part of a chromosome. Aneuploidy is defined as the addition or deletion of all or part of a chromosome. In general, aneuploidy is caused when replicated chromosomes do not accurately segregate between two daughter cells. The defects in the kinetochore, not the presence of a kinetochore, is one mechanism of aneuploidy. E. Correct! Down s syndrome in a male would be identified as 47 (one more than the usual 46 number of chromosomes). Aneuploidy: Addition or deletion of all or part of a chromosome. Aneuploidy happens when replicated chromosomes do not accurately segregate between the two progeny cells. There are a number of mechanisms that can cause an error in chromosome number segregation. These include: A. Abnormal centrosome number leading to multipolar mitosis. B. Chromosome loss at anaphase, due to kinetochore defects. C. Malsegregation of chromosomes at anaphase. D. Mitotic slippage caused by inhibition of mitosis, leading to the formation of tetraploid cells. E. Failure of cytokinesis following nuclear replication. (E)Down s syndrome in a male is identified as 47 XY, 2N+1.

10 No. 10 of What is a Robertsonian translocation? (A) A Robertsonian translocation can occur in any chromosome and it involves a chromosomal deletion. (B) A Robertsonian translocation involves the amplification of part or all of any chromosome in the cell. (C) A non-reciprocal translocation that occurs in chromosome pairs, such as #13 and #22, which are acrocentric. (D) A reciprocal translocation that occurs in a metacentric chromosome. (E) A non-reciprocal translocation involving two telocentric chromosomes. A Robertsonian translocation is a type of non-reciprocal translocation that occurs in the five acrocentric human chromosome pairs. There are five acrocentric human chromosome pairs: 13, 14, 15, 21, and 22. A Robertsonian translocation is a type of non-reciprocal translocation that occurs in the five acrocentric human chromosome pairs. There are five acrocentric human chromosome pairs: 13, 14, 15, 21, and 22. C. Correct! A Robertsonian translocation is a type of non-reciprocal translocation that occurs in chromosome pairs such as #13 and #22, which are acrocentric. It is a type of non-reciprocal translocation that occurs in acrocentric chromosomes. It is a type of non-reciprocal translocation that occurs in acrocentric chromosomes. There are five acrocentric human chromosome pairs: 13, 14, 15, 21, and 22. Robertsonian translocation occurs within these five acrocentric human chromosome pairs. Arms of two acrocentric chromosomes fuse at the centromere and the two short arms are lost. If it occurs in Chromosome 21, it causes Down s syndrome extra chromosome 21 long arm. (C)A non-reciprocal translocation that occurs in chromosome pairs, such as #13 and #22, which are acrocentric.