Biological Sciences Answer Key, Part 2
11. a. DNA stands for deoxyribonucleic acid, which is a molecule that is composed of small chemical compounds known as nucleotides. These nucleotides contain the basic genetic instructions that the cells of each organism uses to help control the organism's growth and development as well as the organism's ability to function normally. As a result, DNA acts as a means of storing an organism's biochemical and physical traits. b. A gene is a set of DNA that can release enzymes to produce ribonucleic acid molecules also known as RNA. RNA is a molecule that an organism uses to create specific proteins that the organism needs to grow, develop, and function properly. c. A locus refers to the specific position of a gene or other genetic structure on a chromosome.
12. The term isomer refers to a molecule that has the same molecular formula as another molecule, but the atoms of the two molecules are not distributed in the same way. In other words, if you have two molecules, molecule A and molecule B, molecule A and molecule B will be isomers if they have the same number of atoms, but the atoms are arranged in a different order. For example, a propan-1-ol molecule has a formula of CH3CH2CH2OH and a propan-2-ol molecule has a formula of C3H8O so the molecules are clearly distributed in a different fashion. However, both molecules actually contain the same amount of carbon, hydrogen, and oxygen as they each have 3 carbon atoms, 8 hydrogen atoms, and 1 oxygen atom. Since both molecules actually contain the same atoms in the same number, but in a different sequence, propan-1-ol and propan-2-ol are isomers.
13. According to the information included in the passage, the correct answer for this particular question is choice "D" as a person with cystic fibrosis must have two CTFR genes that are not working correctly. It may appear as if the passage does not present the information necessary to answer this question, but the answer is actually located in the first line of the passage. The word "recessive" refers to the fact that the disease is linked to a recessive gene and therefore the disease can only occur if two recessive genes are present. Since the passage states that the disease occurs due to a mutation that causes the CTFR genes to malfunction and the disease is recessive, it must take two genes that are not working correctly for the disease to occur.
14. According to the information included in the passage, the correct answer for this particular question is choice "D" as both options A and B are actually correct. This means that a person without cystic fibrosis must have either one dominant gene and one recessive gene or two dominant genes. This is because cystic fibrosis, according to the passage, is a recessive disease so it can only occur if the individual has two recessive genes. As a result, an individual with one dominant CTFR gene and one recessive CTFR gene or an individual with two dominant CTFR genes will not have cystic fibrosis because the individual does not have the two recessive genes, or in other words the two malfunctioning CTFR genes, that are required in order to develop the disease.
15. According to the information included in the passage, the correct answer for this particular question is choice "B" as an individual with cystic fibrosis must have parents that both have at least one recessive CTFR gene. This is because cystic fibrosis, according to the passage, is a recessive disease, which means that the disease occurs in individuals that have two recessive genes. However, this does not necessarily mean that both parents have to have cystic fibrosis as it is possible for each parent to pass one recessive gene to a child thereby causing the child to have two recessive genes. As a result, even though it may appear as if choice "D" is correct, it is actually incorrect for this particular question because an individual with cystic fibrosis does not necessarily need to have parents that have cystic fibrosis.
16. According to the information included in the passage, the correct answer for this particular question is choice "A" as the likelihood that a child will inherit cystic fibrosis if his or her parents each have one recessive gene is approximately 1 in 4 or 25%. This is because each parent will pass one type of CTFR gene to the child, which can result in one of four possible combinations for two parents that each have one recessive gene and one dominant gene. In other words, the child may receive one recessive gene from the mother and one recessive gene from the father, one recessive gene from the mother and one dominant gene from the father, one recessive gene from the father and one dominant gene from the mother, or one dominant gene from the mother and one dominant gene from the father. Since the only combination that will cause the disease is the combination with two recessive genes, there is 1 combination out of 4 that will cause the disease.
17. According to the information included in the passage, the correct answer for this particular question is actually choice "D" as the likelihood that a child will inherit cystic fibrosis if his or her parents each have one recessive gene is approximately 4 in 4 or 100%. This is because each parent will pass one type of CTFR gene to the child, and since both parents only have recessive CTFR genes, the only type of gene that the parents can pass on is a recessive gene. As a result, regardless of exactly which gene gets passed on to the child from each parent, the likelihood of the child having cystic fibrosis is near 100% as the child will have two recessive genes.
18. The correct answer for this particular question is choice "A" as the word autosomal actually refers to the fact that the recessive gene is found on chromosomes that are not related to determining the individual's gender. In other words, an autosomal chromosome is a chromosome that does not affect the child's sexual development and has no bearing on whether the child is born male or female. Autosomal chromosomes are actually the opposite of sex chromosomes as autosomal chromosomes possess identical genes in both males and females and sex chromosomes contain genes that are gender-specific. In this particular instance, the word autosomal is related to the location of the recessive gene, but not specifically to the disease itself so the context of the passage does not actually help identify the meaning of the word. Autosomal is a basic term related to genetics and basic Mendelian concepts, however, so the question assumes that the individual knows the term.
19. The correct answer for this particular question is choice "A" as the word mutation refers to the fact that the base pair of the DNA sequence for the gene has been altered. In other words, at some point, the original genetic coding for the gene that instructed the gene to function in a certain way was changed so the gene functioned in a different way. As a result, choices "B" and "C" are completely incorrect as a mutation refers to a change that has occurred to the gene at a certain point rather than ongoing changes as suggested in choice "B" and a mutation refers to a gene that has changed rather than a gene in its original state so choice "C" is also incorrect. Finally, choice "D" may appear to be correct, and it is in fact correct in some circumstances, but some mutations may actually result in a gene functioning in a different, but equally effective manner so choice "D" is not necessarily an accurate description of a mutation.
20. The correct answer for this particular question is choice "D" as the water and salt buildup mentioned in the passage leads to thick mucous secretions that can block airways and glands, cause sinus infections, and cause damage to vital organs. Even though the passage never lists the effects of cystic fibrosis, an overabundance of mucous or any other fluid within the body can cause blockages, additional pressure, and create a breeding ground for bacteria. Blockages caused by excessive mucous can hinder the individual's ability to breath normally, can prevent enzymes from moving to and from various organs and glands correctly, and can damage vital organs due to the pressure exerted by the mucous and the other fluids that build up as a result of the blockage. The bacterium that breeds in the excess mucous and fluid will also increase the individual's risk of developing sinus infections as it is much easier for the bacteria to breed and infect the mucous membranes.
