Evolution Chapter Six : Exam Two

One of the important facts learned from experiments in molecular genetics is that most amino acids can be encoded by more than one nucleotide triplet. For this reason, we say that the genetic code is __________. A) degenerate B)overlapping C)perfect D)flawed

A) As shown in Figure 6.7, most amino acids can be encoded by more than one nucleotide triplet. There are 20 amino acids, and since there are four different mRNA nucleotides (A, U, G, C) and three bases in a codon and the genetic code is not overlapping, there are 64 (= 43) possible combinations. For this reason, we say that the genetic code is degenerate (degeneracy here refers to redundancy). Given the redundancy of coding for amino acids, many nucleotide changes at the third position of a codon do not change the amino acid that is specified by the codon. This redundancy has a very important evolutionary consequence when it comes to mutation.

In sickle cell anemia, a point mutation leads to a replacement of one amino acid in a hemoglobin molecule, in a unit responsible for transportation of oxygen. This and any other mutation in a gene that causes a change in the amino acid sequence in a polypeptide chain is known as a __________ mutation. A)missense B)nonsense C)silent D)synonymous

A) If the substitution causes the production of a different amino acid, such as in the case of sickle cell anemia, it is known as a missense mutation. If a base substitution does not change the amino acid that a codon normally produces, it is known as a synonymous mutation (also called a silent mutation). Finally, if a base substitution creates a stop codon where there was none previously, it is known as a nonsense mutation. Read the subsection titled "Genetic Variability and Mutation" in Section 6.3 and examine Figure 6.15.

If a DNA sequence of the template strand (in the 3'-5' direction) reads ATG, what would be the corresponding mRNA codon (in the 5'-3' direction)? A) UAC B) TAC C)CAT D) CAU

A) the template strand (used to synthesize/make a complementary RNA strand) will transcribe(process of going from DNA to mRNA) to UAC since A binds with U in RNA. The orientation of the strand is also important, so if the question asked for the 3'-5' mRNA codon, the answer would be CAU. Read the subsection titled "From DNA to Proteins" in Section 6.2 and examine Figure 6.5 on the process of transcription.

The fruit fly (Drosophila melanogaster) has four pairs of chromosomes. How many chromosomes would you find in an unfertilized egg (female gamete or sex cell) of this species? A) 2 B) 4 C) 6 D) 8

B) Reproductive cells in animals and other eukaryotes are formed during the process of meiosis. Somatic cells have 2n chromosomes (in a diploid species such as the fruit fly), while gametes have n chromosomes (haploid, or half of the diploid number). If a somatic number of chromosomes is eight (four pairs), the egg will have four chromosomes (or one of each). Read the subsection titled "Genetic Variability and Recombination" in Section 6.3. In addition, you could draw a map of Drosophila oogenesis, starting with four pairs of chromosomes and finishing with four haploid cells. For a better understanding of meiosis, number each of the four chromosomes and color-code the chromosome pairs.

A type of mutation in which a region of one chromosome is moved to a different chromosome is called __________. A)deletion B)Translocation C)Duplication D) Inversion

B) Translocation is a mutation where a section of 1 chromosome moves to a nonhomologous chromosome (they could = reciprocal if there is an exchange between nonhomologous chromosomes which means that two different chromosomes have exchanged segments with each other).A) Deletion entails the loss of a large section of a chromosome. C)Duplication refers to an addition to chromosomal segment which will add genetic material. D) Inversion means that there is a 180 deg, flip in a section of the chromosome. Figure 6.17 as depicted illustrates the variety of chromosomal aberrations (which means departure from what is normal)

A mutation that results in a replacement of a purine with a pyrimidine is known as a __________ mutation. A) neutral B) Transversion C)Transition D)frameshift

B) When a purine is replaced with a pyrimidine or vice versa it is called transversion. When a purine is replaced by a purine or when a pyrimidine is replaced by a pyrimidine, it is called transition.In section 6.3 titled variation and mutation its clearly emphasizes the difference between the two in the image (only transversion is depicted here).

Which position in a codon shows the greatest degeneracy? In other words, if a change occurs in this codon position, it is less likely to change the amino acid that is specified relative to the other positions. A)All positions are equally degenerate. B)first position C) third position D) second position

C) As illustrated in Figure 6.7 on the genetic code, most amino acids can be encoded by more than one nucleotide triplet; for this reason, we say that the genetic code is redundant, or degenerate. Given the redundancy of coding for amino acids, many nucleotide changes at the third position of a codon do not change the amino acid that is specified by the codon.

Which of the following is TRUE regarding the difference between a DNA molecule and an RNA molecule? DNA contains only purines, whereas RNA contains only pyrimidines. A)DNA contains purine and pyrimidine bases, whereas RNA B)contains only purines. C)DNA is a double-stranded molecule, whereas RNA is a single-stranded molecule. D)DNA contains uracil, whereas RNA contains thymine.

C) DNA is a macromolecule composed of repeating units called nucleotides (including adenine, guanine, cytosine, and thymine) linked together in a chain. Each nucleotide is composed of a five-carbon sugar known as deoxyribose, a phosphate group, and a nitrogenous base. Adenine and guanine are purines, whereas cytosine and thymine are pyrimidines. DNA is a double-stranded molecule; RNA is similar to DNA, but single-stranded. Moreover, it contains a nucleotide called uracil instead of thymine. Read the subsection titled "DNA and Chromosomes" in Section 6.2 and review Figure 6.4.

An addition or deletion of one or two base pairs in a gene sequence results in a __________ mutation. A)transversion B)transition C) frameshift D) Nonsense

C) frameshift because codons = three nucleotides and when an insertion or deletion mutation occurs and involves an number of codons ≠ to a multiple of three it produces a frameshift mutation. This affects the translocation of other codons and affects amino acid and protein production. When a insertion or deletion involves a multiple of three nucleotides, it does not disrupt the reading frame: which defines, the way adjacent base pairs are grouped into triplets and translated into amino acids. Figure 6.16 examines in-frame and frameshift mutations.

In the 1850s and 1860s, Gregor Mendel bred pea plants and examined the way that traits were passed down across generations. His conclusions, although not accepted during his lifetime, established the foundation for the field of genetics. Of the choices listed, what is the most relevant summary of Mendel's conclusions? A)Recessive factors of inheritance blend after the first filial generation. B)Hereditary material must be a nucleic acid. C) The hereditary factors responsible for traits such as seed shape and flower color are inherited as discrete units. D) Garden pea plants are the best experimental model system to study heredity.

C) n the mid-1800s, a predominant view among naturalists was that traits blend together and therefore could be lost in future generations. This understanding of heredity was a limitation for Charles Darwin's theory, and although Mendel and Darwin worked at about the same time, they did not know of one another. Mendel was an Augustinian monk and a plant breeder in the Austro-Hungarian Empire. With his fine mathematical skills, Mendel established the first genetic experiment and the discipline of genetic analysis. In his experimental research with tens of thousands of pea plants that he had bred, he concluded that traits do not blend, but rather that they are discrete in nature. Mendel named his discrete entities "factors of heredity" (today known as genes). Almost a century later, it became clear that genes are composed of DNA.

Which of Gregor Mendel's laws contradicts the blending theory of inheritance? A)Mendel's second law, the law of independent assortment B)Blending theory is not contradicted by Mendel's laws. C)Mendel's first law, the law of segregation D) Mendel's law of transmission genetics

C)Mendel's first law, the law of segregation, was derived from data on different crosses that Mendel performed with pea plants. This law states that each individual has two gene copies at each locus (the physical location of genes on the chromosome) and that these gene copies segregate during gamete production so that only one gene copy goes into each gamete. See Figures 6.2 and 6.3 on blending inheritance versus particulate inheritance.

If an mRNA sequence in the 5'-3' direction usually begins UGG AUG UCG CCC AUA, what would you expect to happen if the guanine in the third position is deleted from the mRNA sequence? A)The correct amino acid will be added in the first position. B)Tryptophan will be the first amino acid added to the chain. C) The mRNA will not be translated into a protein at all. D) The incorrect amino acid will be added in the first position.

C)This figure specifies the relation between codon triplets and amino acids they make.To read this fig, start at the inside of the circle and move outward! When the guanine in the third position is deleted, the new sequence begins UGA, which is a stop codon; this then shifts the reading frame for AUG, which is the necessary start codon. This means the mRNA will not be translated and the protein will not be made.

Suppose that in wild rose plants, the A locus controls pigmentation of the flower petals. The A allele (for red flower coloration) is completely dominant to the a allele (for pale pink flower coloration). If purebred red-flowered plants were crossed with purebred pink-flowered plants, and their heterozygous offspring (the F1 generation) were grown so that such hybrids might be crossed among themselves, which of the following flower phenotypes might you expect in the F2 generation? A)both red and pale pink roses (in a ratio of 1:1) B)pale pink roses only C) red roses only D) both red and pale pink roses (in a ratio of 3:1, respectively)

D) For this question, you need to use the concept of a genetic experiment (P, F1, and F2 generations, starting with purebred lines—AA × aa). You can also use a Punnett square. For example, Figure 6.10 shows the Punnett square for a cross involving a single trait that has a recessive allele and a dominant allele. If the parental generation AA (red) is crossed with aa (pale pink), the F1 generation will be 100% Aa heterozygotes with red flowers. If two Aa (red) flowered plants are crossed, their offspring (the F2 generation) will be 25% AA, 50% Aa, and 25% aa; this results in 75% red and 25% pale pink flowered plants in the F2 generation.

The graph shows the distribution of fitness effects of Bacteriophage f1 mutants. Note that values greater than 1.0 indicate beneficial mutations, whereas values less than 1.0 indicate deleterious mutations. What is the best conclusion from this study? A) The proportion of neutral mutations and beneficial mutations was equal. B)The proportion of beneficial mutations and deleterious mutations was equal. C)The majority of mutations in the bacteriophage were beneficial. D) The vast majority of the mutations had a deleterious effect, but some were beneficial.

D) Joan Peris and her colleagues found that in the virus Bacteriophage f1, approximately two-thirds of the mutations caused a change in the amino acid that was produced (Peris et al. 2010). The majority of those mutations that had a non-neutral effect on fitness were deleterious. However, a few mutations were beneficial. Focus on Figure 6.23 and consider how this helps us to better understand Charles Darwin's theory of natural selection in light of the new data regarding mutations and fitness.

In their experiment in 1943 using E. coli, Salvador Luria and Max Delbrück tested two alternative hypotheses. The random mutation hypothesis and the acquired inherited resistance hypothesis make different predictions about the distribution of resistant mutants that will be observed upon exposure to bacteriophage (viruses that can infect and kill E. coli). Which of the following predictions, if proven, would support the acquired inherited resistance hypothesis? A)Regardless of the origin of these mutations, resistance to the phage will be heritable and will result in colonies of phage-resistant E. coli cells. B)There will be wide variation in the number of phage-resistant E. coli colonies on each agar plate. C)The phage-resistant E. coli cells will arise by random mutation even before the phage is present. D)At the time of exposure to the phage, all E. coli cells will be phage-sensitive. The process of exposure to the phage will induce phage resistance in a small fraction of the bacterial cells.

D) Luria and Delbrück proposed two hypotheses. The first one (random mutation) predicts that prior to exposure to the phage, a few resistant E. coli cells will arise by random mutation. Once exposed to the phage, most cells will be killed, but the resistant cells will not. Instead they will reproduce and form new resistant colonies. The second hypothesis (acquired inherited resistance) proposes that at the time of exposure to the phage, all bacterial cells will be phage-sensitive. The process of exposure to the phage will induce phage resistance in a small fraction of the bacterial cells. This resistance will then be heritable, and the cells with induced resistance will go on to produce colonies of resistant cells. Compare the two hypotheses in Figures 6.20 and 6.21.

The purple flower of the F1 offspring of Gregor Mendel's parental generation crosses indicated that __________. A)the parental generation is heterozygous for the flower color character B)white color in flowers is dominant to purple color the F1 generation is homozygous for the flower color character D)purple color in flowers is dominant to white color

D) Mendel's protocol was simple but powerful. In the true-breeding parental generation, he crossed a parent plant homozygous for purple flowers with a parent plant homozygous for white flowers. All of the offspring from these matings—known as the F1 generation (the first generation of offspring)—produced purple flowers even though they contained a copy of genetic information from both parents, one of which produced white flowers. Because of this, Mendel concluded that purple color in pea flowers was dominant to white color; that is, purple flower color appeared when both gene copies were purple or when one was purple and the other white. See Figure 6.1.

Gene expression in eukaryotes is strongly influenced by the local structure of the chromosome. In which of the following regions of a DNA molecule would you expect to find the highest levels of gene expression? A)histones B)methyl groups C)condensed chromatin D) decondensed chromatin

D) The chromosome is structured as chromatin not free DNA. DNA winds around histones ( a protein). Where chromatin is condensed ( tightly packed) a gene's promoter)is not able to access RNA polymerase and the gene is not expressed (unexpressed). Where chromatin is decondensed the RNA polymerase can bind to the promoter and the gene can be transcribed, this region has the highest level of gene expression.See figure 6.11. Sidenote: Promoter means ( —a short DNA sequence before the transcribed part of the gene—and this serves as a signal to begin transcription.

A mutation resulting in deletion of a protein-coding gene will most likely have a ___________ effect on fitness. A)neutral B) lethal C) beneficial D) deleterious

D) because from evolutionary perspective, the most imp way to categorize mutations is in terms of their effect on fitness. Many mutations can be A,C or D but the effect of D (gene deletion) is not expected to be lethal. However with genes involved w/h mjr metabolic pathways it might be.

If one human protein contains 400 amino acids, how many nucleotides need to be in the exons of the corresponding gene to properly code for it? A)120 B)400 C)40 D)1200

D)The genetic code specifies the relation between codon triplets and the amino acids for which they code. If a polypeptide (primary structure of a protein) is 400 amino acids long, there should also be at least 400 codons in the corresponding mRNA. Each codon consists of three nucleotides, so 400 × 3 = 1200. The gene itself might be much longer than 1200 base pairs though because, at least in eukaryotes, the processed mRNA corresponds with exon sequences.

According to the figure, which of the following statements regarding base substitution mutation rates is FALSE? A)Among cellular organisms, base substitution mutation rates increase with increasing genome size. B)In viruses, base substitution mutation rates increase with increasing genome size. C)RNA viruses tend to have higher base substitution mutation rates than DNA viruses. D)The data shown indicate that mammals have higher base substitution mutation rates than do invertebrate animals.

The answer is : the letter that comes after A ( so B). It is false because in viruses, base substitution mutation rates do not increase with increasing genome size. If you look at the diagram and observe the pink and red dots you'll notice that as base substitution mutation rates increase the genome size decreased for viruses. Reasoning: In figure 6.22, we see the base substitution mutation rate per nucleotide site per generation as a function of genome size, in microbes (chart A) and in cellular organisms ( chart B). Among microbes, mutation rate decreases with genome size, in cellular organisms mutation rates increase with genome size. Mutation rates also vary widely in different regions of a single genome ( genome = a complete set of genes in a cell). They vary widely between nuclear and organellar genomes, between sexes,between families and across diff. tissue types within the same species.