Mutations and Genetic Variability. 1. What is occurring in the diagram below?

Transcription

1 Mutations and Genetic Variability 1. What is occurring in the diagram below? A. Sister chromatids are separating. B. Alleles are independently assorting. C. Genes are replicating. D. Segments of DNA are crossing over.

2 2. The chart below shows the codons that make up the genetic code and the sequence of nucleotides that corresponds to them. A mistake during DNA replication leads to a mutation in the nucleotide sequence shown below. This mutation results from the insertion of two nucleotides into the original sequence, which causes the reading frame of the sequence to change. This kind of mutation is known as A. a nonsense mutation. B. a silent mutation. C. a chromosomal mutation. D. a frame shift mutation.

3 3. Dr. Stevens is examining the DNA sequences of a group of mice. He notices that in one of the mice, one nucleotide pair is substituted with another in the part of the DNA sequence that codes for fur color. However, despite the substitution, the mouse still has the same fur color as the other mice with the correct DNA sequence. Why doesn't the substitution of nucleotides in the mouse change its phenotype, or physical characteristics? The mouse has a completely different DNA sequence than the other mice. A. The substituted nucleotide has the same directions as the original nucleotide. B. Substitutions in the nucleotides of a mouse's DNA never affect their phenotypes. C. DNA sequences don't determine the color of a mouse's fur. D. 4. Which of the following is a source of genetic variation in sexually-reproducing organisms? A. mitosis B. translation C. meiosis D. all of these 5. Most heritable differences are due to A. the insertion of incorrect sequences of DNA by faulty polymerases. B. point mutations that occur during mitosis. C. the inability to form proper DNA sequences due to poor nutrition. D. gene shuffling that occurs during the production of gametes.

4 6. The chart below shows the codons that make up the genetic code and the sequence of nucleotides that corresponds to them. A mistake during DNA replication leads to a mutation in the nucleotide sequence shown below. What kind of mutation will result from the mistake made during DNA replication in the nucleotide sequence above? A. a frame shift mutation B. a nonsense mutation C. a silent mutation D. a chromosomal mutation

5 7. A frame shift mutation is a genetic mutation that is caused by the insertion or deletion of a specific number of nucleotides that shifts the reading frame of the sequence. The insertion or deletion of how many nucleotides would cause a frame shift mutation? A. 3 B. 2 C. 9 D How do mutations lead to genetic variation? A. by changing the organism's appearance B. by changing the way that the organism reproduces C. by changing the organism's behavior D. by producing random changes in an organism's genetic code 9. How could an apple farmer increase the number of genotypes and phenotypes present in his next apple crop? A. Cross plants that have the same characteristics. B. Cross plants that have very different characteristics. C. Make genetic clones of plants using asexual reproduction. D. It would be impossible for a farmer to increase the genetic variation of plants.

6 10. Down syndrome is a genetic disorder that is typically caused by an extra copy of chromosome 21 in a person's genome. In a small number of cases, however, Down syndrome occurs because a section of chromosome 21 becomes fused onto another chromosome. The type of Down syndrome that occurs because a section of chromosome 21 attaches to another chromosome is an example of a genetic disorder caused by A. chromosome deletion. B. chromosome translocation. C. a recessive allele. D. a frame shift mutation. 11. Triple X syndrome, or trisomy X, occurs when a female has an extra X chromosome in each of her cells. This results when the mother's reproductive cells divide improperly, and two X chromosome are moved into one gamete. When that gamete is fertilized and the father's DNA and X chromosome are combined with the mother's, that gives the cell three X chromosomes instead of two. Triple X syndrome occurs because of. A. deletions B. crossing over C. point mutations D. nondisjunction 12. Technology Enhanced Questions are not available in Word format. 13. During meiosis, the process of crossing over results in new combinations of alleles because A. genetic material always mutates randomly during this process. B. genetic material is added by a third chromosome during this process. C. genetic material is removed during this process. D. genetic material is exchanged between chromosomes during this process.

7 14. Organisms are able to reproduce either sexually or asexually. Which of the following statements is true of these reproductive processes? The sorting of genes during sexual reproduction results in a large amount of genetic variation. A. During every cell division in sexual reproduction, the number of chromosomes is reduced by half. B. During every cell division in asexual reproduction, the number of chromosomes is reduced by half. C. The sorting of genes during asexual reproduction results in a large amount of genetic variation. D. 15. The diagram below illustrates a process that can occur during cell division and results in an alteration in the composition of a chromosome. Each letter in the diagram represents a specific gene on the chromosome. The diagram shows that a section of the chromosome was broken out and reinserted backwards. This is known as A. chromosome translocation. B. chromosome insertion. C. chromosome inversion. D. chromosome deletion.

8 16. The diagram below shows a process that can result in the alteration of the composition of chromosomes. A piece of each chromosome in the diagram has broken off and been reattached to the other chromosome, resulting in an exchange. The process that occurs when a section of a chromosome breaks off and reattaches to another chromosome is known as. A. chromosome nondisjunction B. chromosome deletion C. chromosome inversion D. chromosome translocation 17. A genetic mutation that causes a codon that should code for a specific amino acid to be changed into a stop codon results in a shortened protein product and is known as A. a frame shift mutation. B. a silent mutation. C. a nonsense mutation. D. a chromosomal mutation. 18. Technology Enhanced Questions are not available in Word format.

9 Disease Characteristics Cause Cri-du-chat Syndrome (Cry of the Cat) improperly developed larynx babies cry like distressed cats severe mental retardation small round faces small cranium deletion of parts of chromosome 5 Edward's Syndrome (Trisomy 18) severe mental retardation elongated skull very narrow pelvis feet with round bottoms two central fingers grasped by thumb and little finger death in early infancy extra chromosome 18 Down Syndome (Trisomy 21) mild to severe retardation short height broad hands stubby fingers and toes round face large protruding tongue speech difficulties extra chromosome 21 Down Syndrome (14-21 Translocation) same as Trisomy 21 extra chromosome 21 attached to chromosome 14 Turner's Syndrome (XO) female appearance infertility lack of a second sex chromosome Klinefelter's Syndrome (XXY) female characteristics infertility extra X chromosome 19. A cat's coloring is mostly determined by genes on their X chromosomes, which contain alleles for colors, such as black, orange, gray, and cream. The allele for white fur is located on a different gene.calico cats, by definition, must display three different colors in their fur - white plus two of the other colors. This is easily possible in female cats, because females normally possess two X chromosomes. However, this occurs rarely in male cats, because males typically possess only one X chromosome plus one Y chromosome.what must be the genetic make-up of a male calico cat, and what type of chromosome disorder does this most resemble? A. XO, Turner's syndrome B. XX, Down's syndrome C. XYY, Cri-du-chat syndrome D. XXY, Klinefelter's syndrome 20. Errors that are made during DNA replication may result in

10 A. a viral infection. B. mutations. C. identical twins. D. radioactive decay. 21. Technology Enhanced Questions are not available in Word format. 22. A genetic mutation that does not result in a change in the amino acid sequence of the resulting protein is called A. a silent mutation. B. a frame shift mutation. C. a nonsense mutation. D. a chromosomal mutation.

11 The table below shows various DNA codons and their corresponding amino acids. Amino Acid DNA Codon(s) Alanine GCT, GCC, GCA, GCG Arginine AGA, AGG, CGT, CGC, CGA, CGG Asparagine AAT, AAC Aspartic Acid GAT, GAC Cysteine TGT, TGC Glutamic Acid GAA, GAG Glutamine CAA, CAG Glycine GGT, GGC, GGA, GGG Histadine CAT, CAC Isoleucine ATT, ATC, ATA Leucine CTT, CTC, CTA, CTG, TTA, TTG Lysine AAA, AAG Methionine (Start) ATG Phenylalanine TTT, TTC Proline CCT, CCC, CCA, CCG Serine TCT, TCC, TCA, TCG, AGT, AGC Threonine ACT, ACC, ACA, ACG Tryptophan TGG Tyrosine TAT, TAC Valine GTT, GTC, GTA, GTG Stop TAA, TAG, TGA 23. In the DNA strand below, two nucleotides were reversed during replication. What will happen when the replicated DNA strand is translated into proteins? A. No proteins will be formed at all. B. Nothing will happen. C. The same protein, isoleucine, will be formed. D. Tyrosine will be formed instead of isoleucine.

12 24. An organism's genotype describes its specific combination of alleles. For example, an Aa genotype is heterozygous for the A allele. An organism's phenotype describes a visible trait, such as tall height, brown eyes, or black fur. How does genotypic variation occur? Genotypic variation occurs when alleles are randomly sorted during asexual reproduction. A. Genotypic variation occurs when alleles are randomly sorted during sexual reproduction. B. Genotypic variation only occurs when genetic mutations occur. C. Genotypic variation only occurs during binary fission. D.

13 25. The chart below shows the codons that make up the genetic code and the sequence of nucleotides that corresponds to them. A mistake during DNA replication leads to a mutation in the nucleotide sequence shown below. What kind of mutation will result from the mistake made during DNA replication in the nucleotide sequence above? A. nonsense mutation B. silent mutation C. frame shift mutation D. chromosomal mutation

14 26. When environmental conditions change, it is more likely that at least some members of a species will survive if A. the species reproduces asexually. B. the members are genetically identical. C. there is variation among the members. D. the species requires very specific environmental conditions. 27. During meiosis, homologous chromosomes frequently exchange portions of their DNA. This process increases the number of different genotypes that an offspring can inherit. What is the name of this process? A. genetic transfer B. transduction C. crossing-over D. mutation 28. During normal meiosis, homologous chromosomes pair up and separate so that each gamete receives a copy of every chromosome. Sometimes an error is made during this separation and homologous chromosomes fail to separate. This results in one gamete that has two copies of the chromosome, and another gamete that does not have the chromosome at all. This type of error is known as and usually results in zygotes that either do not develop to term or have severe abnormalities. A. chromosome translocation B. chromosome insertion C. chromosome inversion D. chromosome nondisjunction

15 29. is a source of genetic variation that involves the swapping of sections of chromosomes during meiosis. A. Fertilization B. Transcription C. Translation D. Crossing over 30. Technology Enhanced Questions are not available in Word format. Answers 1. D 2. D 3. B 4. C 5. D 6. B 7. B 8. D 9. B 10. B 11. D D 14. A 15. C 16. D 17. C D 20. B A 23. D 24. B 25. B 26. C 27. C 28. D 29. D Explanations 1. In the diagram, segments of DNA from homologous chromosomes are crossing over. This process, which occurs during Prophase I of meiosis, happens randomly and frequently. In fact, it can even occur at more than one place along the same chromosome. Meiosis and crossing-over are important processes because they contribute to the genetic variation found in organisms that undergo sexual reproduction.

16 2. Frame shift mutations cause the reading frame of the sequence to be shifted. Since a codon is a sequence of three nucleotides that code for a specific amino acid, any insertion or deletion that is not a sequence of three causes a frame shift mutation. Insertions or deletions in multiples of 3 will cause a protein to be shorter or longer than normal, but the entire sequence of the amino acids will not be shifted. 3. A mutation (substitution, insertion, deletion, etc.) can cause changes in the phenotype of an organism. These changes may be beneficial and produce organisms that are better suited to their environments, or they may be detrimental. However, in some cases, there is no effect, and a change of phenotype does not occur. If a mutation occurs that does not dramatically change the DNA sequence, it is possible that it can be translated properly into proteins. In this example, the substituted nucleotide provides the same directions as the original nucleotide. This occurs when one nucleotide is replaced with another, but the resulting nucleotide group (codon) still codes for the same protein. If the protein that is made is the same as it would normally be, the mutation is called a silent mutation, and the organism's phenotype will be normal. 4. In sexually-reproducing organisms, meiosis helps contribute to genetic variation. Meiosis is the process by which sexually-reproducing organisms produce gametes, or sex cells. Meiosis produces gametes that are unique from each other and from the "parent genome". The gametes will be passed on to future offspring. 5. Many factors can cause a change in a gene over time. However, most heritable differences are due to gene shuffling that occurs during the production of gametes. Gametes are produced when cells undergo meiosis. Mutations or changes in DNA sequences can occur spontaneously, but this happens infrequently. 6. As shown in the chart, UGU codes for cysteine (Cys), but the mutated mrna codon, UGA, is a stop codon, which signals the end of transcription. This is a nonsense mutation, which is a mutation that changes a codon that codes for a specific amino acid into a stop codon. If the mutation occurs during DNA replication, the mrna strand that is produced will result in a shortened protein product. The earlier in a nucleotide sequence that this mutation occurs, the shorter the resulting protein will be. 7. Frame shift mutations cause the reading frame of the sequence to be shifted. Since a codon is a sequence of three nucleotides that code for a specific amino acid, any insertion or deletion that is not a sequence of three causes a frame shift mutation. Therefore, the insertion or deletion of 2 nucleotides would cause a frame shift mutation. Insertions or deletions in multiples of 3 will cause a protein to be shorter or longer than normal, but the entire sequence of the amino acids will not be shifted. 8. A mutation is a random change in a cell's genetic code due to a variety of causes. The change can be small and insignificant, or it can be major. Mutations can be passed on to offspring through reproduction, thus increasing the genetic variation within a population. 9. Farmers can enhance the genotypic variety of their crops by crossing crops with very different characteristics, resulting in new combinations of alleles. This genotypic variety will result in phenotypic variety. 10. Chromosome translocation is caused when material is exchanged between two chromosomes or part of one chromosome becomes fused onto another chromosome. Some human disorders are caused by chromosome translocation, such as cancer, infertility, and translocation Down syndrome.

17 Translocation Down syndrome is caused by a piece of chromosome 21 fusing onto another chromosome. It accounts for less than 5% of the total cases of Down syndrome reported. 11. Syndromes such as triple X syndrome, Turner's syndrome, Down syndrome, and Klinefelter's syndrome occur because of nondisjunction, or the improper separation of the chromosomes during division. In each of these cases, an extra chromosome (X chromosome for triple X, chromosome 21 for Down syndrome, etc.) causes symptoms in the offspring. In some syndromes, such as triple X syndrome, the symptoms are often not very noticeable During meiosis, the process of crossing over results in new combinations of alleles because genetic material is exchanged between homologous chromosomes during this process. When crossing over occurs, different parts of chromosomes are exchanged, meaning that genes (and their alleles) are transferred to new chromosomes. When meiosis separates these chromosomes, the new combination of alleles is transferred to the offspring, resulting in a new combination of traits. 14. Binary fission, budding, and spore formation are all examples of asexual reproduction. This form of reproduction is prevalent among single-celled organisms and some plants and fungi. Although asexual reproduction is faster and requires less energy than sexual reproduction, offspring are almost always genetically identical to their parents; there is little to no genetic variation. Sexual reproduction requires the formation of gametes (e.g. sperm and egg) during the process of meiosis. The advantage of sexual reproduction is that a great variety of possible gene combinations can be produced in the offspring of any two parents. This variety is due to the sorting and recombination of genes that occurs during meiosis. 15. Chromosome inversion occurs when a section of the chromosome breaks out and is reinserted backwards. Inversions usually do not cause physical or mental abnormalities in an individual as long as no genetic information is lost during the inversion. 16. Chromosome translocation occurs when a section of a chromosome breaks off and is added to a different chromosome. The type of chromosome translocation shown in the diagram is known as reciprocal translocation, which involves the exchange of material between two chromosomes. Reciprocal translocations are the most common type of translocation and do not result in a loss of genetic information. 17. A nonsense mutation is a mutation that changes a codon that codes for a specific amino acid into a stop codon. This results in a shortened protein product. The earlier in a nucleotide sequence that this mutation occurs, the shorter the resulting protein will be As mentioned in the question, a calico pattern can only result if a cat has two X chromosomes, but in order for a cat to be male, it must also possess a Y chromosome. So, a male calico cat must have XXY chromosomes. This pattern is also possessed by humans with Klinefelter's syndrome. 20. Errors that are made during DNA replication may result in mutations. Mutations are a source of variation within species. Some mutations are harmless, while others may be harmful to an organism

18 22. A silent mutation is a mutation that does not result in a change in the amino acid sequence of the resulting protein. Most amino acids are coded by several different codon sequences. Therefore, a mutation can occur that changes the nucleotide sequence, but does not change the resulting amino acid. These mutations are referred to as silent because they do not change the product of protein translation and cannot be detected without sequencing the gene. 23. If two or more nucleotides are reversed, it is possible for the same protein to be translated, or a different protein may be translated. In this case, ATT codes for isoleucine, whereas TAT codes for tyrosine. So, tyrosine will be formed instead of isoleucine. If the T in the 5th position and the T in the 6th position had been reversed, however, the same codon (ATT) would have resulted, and the same protein would have been translated. When a mutation occurs that does not affect the amino acid sequence of a protein, it is known as a silent mutation. 24. Genotypic variation occurs when alleles are randomly sorted during sexual reproduction. Since each offspring receives a different combination of alleles from the parent organisms, phenotypic diversity results. Genotypic and phenotypic traits can be predicted using Punnett squares. 25. As shown on the chart, both CCU and CCC code for proline (Pro). This means that the mistake made during DNA replication in the nucleotide sequence in the question will result in a silent mutation, which is a mutation that does not result in a change in the amino acid sequence of the resulting protein. Most amino acids are coded by several different codon sequences. Therefore, a mutation can occur that changes the nucleotide sequence, but does not change the resulting amino acid. These mutations are referred to as silent because they do not change the product of protein translation and cannot be detected without sequencing the gene. 26. When environmental conditions change, it is more likely that at least some members of a species will survive if there is variation among the members. This is because the variant organisms within the species are able to respond differently to the environmental changes. 27. Crossing-over is a process that typically occurs during prophase I of meiosis. During this phase, homologous chromosomes are held tightly together which enables the exchange of segments of DNA. Crossing-over is an important process because it introduces more genetic variation into a species. 28. Chromosome nondisjunction occurs when homologous chromosomes fail to separate during meiosis. The result of chromosome nondisjuction is the formation of one gamete that does not have the chromosome and another gamete that has two copies of the chromosome. Zygotes that have a gamete lacking a chromosome usually do not develop to term. Zygotes that have a gamete with two copies of a chromosome, along with a normal gamete, have a total of three copies of a chromosome and sometimes do develop, although they often have severe abnormalities. Examples of genetic conditions caused by the presence of three chromosomes (also known as a trisomy) include triple X syndrome, Turner's syndrome, Down syndrome, and Klinefelter's syndrome. 29. Crossing over, which occurs in prophase I of meiosis, is a process by which homologous chromosomes swap homologous segments of DNA. This helps produce gametes that are unique from the "parent genome", thus increasing genetic variation