New York State Chemistry RegentsNew York State Earth Science Regents

Heredity and Genetics
Living Environment Regents June 2010 Question 07 PDF Print E-mail
Thursday, 26 May 2011 15:25
Correct Answer: (2) 35%

In the DNA, the purine bases are adenine (A) and guanine (G), while the pyrimidine bases are thymine (T) and cytosine (C). According to Chargaff's rule, the DNA from any cell of all organisms should have a 1:1 ratio of pyrimidine and purine bases. Thus, %A = %T and %G = %C. Thus, if the DNA sample has 15% T, then it must also contain 15% A. The A-T pair already constitutes 30%, and thus the G-C pair would make up the 70%. Since G is equal to C, then simply divide 70% by 2, then you will get the C% which is 35.

Incorrect Answers:

(1) 15%

(3) 70%

(4) 85 %

All the other options are incorrect because they do not follow the Chargaff's rule of base pairing.

Living Environment Regents June 2010 Question 09 PDF Print E-mail
Thursday, 26 May 2011 15:29
Correct Answer: (2) identical genetic information

Genetic information is contained in the DNA. All DNAs in the body cells are the same, thus, all the structures indicated-skin, eyes and leg muscles-all have identical genetic information.

Incorrect Answers:

(1) equal amounts of ATP

Adenosine triphosphate (ATP) is an adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. Since ATP is the energy currency of the body, there are more ATP found in the leg muscles because they are used for movement compared to those found in the skin and eyes, which both need less amount of energy to function.

(3) proteins that are all identical

The pointed structures are made up proteins. However, these proteins are not the same in all parts because they are arranged and synthesized in a specific manner depending on the function of the body parts. Since the eye, skin, and leg muscles have different functions, thus they are composed of different proteins.

(4) organelles for the synthesis of glucose

The synthesis of glucose or gluconeogenesis occurs only in the liver and kidney cortex, particularly in the mitochondria and cytoplasm organelles. Glucose is not produced in the pointed structures.
Living Environment Regents June 2010 Question 12 PDF Print E-mail
Monday, 30 May 2011 10:28

Correct Answer: (4) genetic engineering

The illustration shows the process of genetic engineering or recombinant DNA technology. The first step in this technique is called DNA extraction. During this process, the DNA from the desired organism in extracted then treated with restriction enzymes which cuts the DNA into smaller portions with defined ends to so that it can be cloned into bacterial vectors. These vectors are transformed into bacterial cells and thousands of copies are produced. After gene cloning, the gene of interest will be linked to other DNA components that will regulate its expression in the cell. Then the gene will be inserted to the bacterial cell through the use of gene gun or Agrobacterium-mediated transformation.

Incorrect Answer:

(1) chromatography

Chromatography is a laboratory technique used to separate mixtures. The sample of the mixture is dissolved in a mobile phase. The mobile phase is then forced through a steady, immiscible stationary phase. The phases are selected so that the components of the sample have differing solubilities in each phase. The component that is soluble in the stationary phase will be slower in moving through it than the component that is not very soluble in the stationary phase but very soluble in the mobile phase. Since they have different rates of movement due to solubility, the components of the sample will be separated from each other as they move through the stationary phase. There are no DNA, plasmid vector, and bacterial cell involved in this process, thus the illustration does not pertain to chromatography.

(2) gel electrophoresis

Gel electrophoresis refers to the process of separating molecules on their differential mobility in an electric field. The smaller molecules move through the gel faster than the larger molecules. In genetic engineering, it is used to separate DNA fragments. Therefore, the illustration does not explain this process.

(3) direct harvesting

Direct harvesting is a technique used in molecular biology usually in collecting samples from the internal parts of the body for analysis. For instance, bone marrow sample is collected through direct harvesting for cancer studies.
Living Environment Regents June 2010 Question 16 PDF Print E-mail
Monday, 30 May 2011 10:37

Correct answer: (3) gene expression may be influenced by factors that switch genes on and off

Identical twins have exactly the same set of genetic information. However, they have different phenotypes or the physical and physiological expression of genes. Thus, identical twins may have differences when exposed to factors that may affect the expression of genes such as the environment.

Incorrect answers:

(1) each twin receives different chromosomes

Since identical twins have the same genetic information, then it also means that they have the same set of chromosomes.

(2) one twin may only have genes from the father

All offsprings have combined genes from the parents because during fertilization, haploid games are united to form a diploid offspring.

(4) gene mutation may have occurred before the zygote divided

Mutation is the rare change in the DNA of genes that ultimately creates genetic diversity. Mutation can be caused by exposure to chemicals or radiation. It is almost impossible for mutation to occur before the zygote divides because the zygote is very small and is inside the female reproductive system.
Living Environment Regents June 2010 Question 21 PDF Print E-mail
Thursday, 26 May 2011 15:36
Correct answer: (1) genetically inherited from parents

If the young birds have been isolated from the other members of the species but still exhibit the same behavior with their kind, then that characteristic must be due to their genes. Behavior is controlled by complex traits and it is species-specific.

Incorrect answers:

(2) learned by watching members of their species

This cannot be true because the young birds have been isolated from their kind, thus, they cannot copy the behavior of the species in the original location.

(3) a disadvantage to the survival of the species

Since the behavior which has been tried and tested is still used, then the species would have high chance of continuing its kind. But if the species starts to change its behavior apart from its kind, then evolution could occur, and new species could arise making the old species extinct.

(4) a direct result of the type of food the bird eats

Food has no effect on the nest-building behavior of the birds. Behaviors are regulated by complex traits not by the food that the birds eat.

Living Environment Regents June 2010 Question 34 PDF Print E-mail
Thursday, 26 May 2011 16:10
Correct answer: (1) deletion-substitution-insertion

Mutations are changes in the genetic makeup of a cell.Point mutation is a type of mutation caused by chemical changes that occurs in a single base nucleotide in a single gene. This type of mutation could be a deletion, insertion, or substitution of a nucleotide. Mutation A illustrates a deletion, wherein one nucleotide is lost. The normal sequence has 9 nucleotides, while the resulting sequence after mutation only contains 8 nucleotides.

Mutation B represents substitution, wherein one nucleotide is replaced with another nucleotide. The first nucleotide in the normal sequence is cytosine (C), and then it was substituted with guanine (G) after mutation occurred.

Mutation C shows an example of insertion because there was an additional nucleotide in the mutated sequence. The normal sequence contains only 9 nucleotides, while the mutated sequence already has 10 nucleotides.

Among these three types, deletion and insertion could be harmful to the organism.

Incorrect answers:

(2) insertion-substitution-deletion

Mutation A could not be considered as insertion because there is no additional nucleotide in the sequence, while mutation C is not an example of deletion because no nucleotide was added in the sequence.

(3) insertion-deletion-substitution

Mutation A is not an example of insertion because there was no addition of a nucleotide. Mutation B is not considered as deletion because the mutated sequence has the same number of nucleotides with the normal sequence. An additional nucleotide was exhibited in mutation C; thus it is insertion, not substitution.

(4) deletion-insertion-substitution

There is no additional nucleotide in mutation B that is why it is not considered as an insertion. There is an additional nucleotide in mutation C, thus it is insertion, not substitution.
Living Environment Regents June 2010 Question 55 PDF Print E-mail
Thursday, 26 May 2011 17:13

Type of gamete: ZW

In birds and some fishes, the variable that determines sex is the sex chromosome present in the ovum, not in the sperm. The males are ZZ and females are ZW. The female gamete ZW determines the sex of the offspring because it is composed of two different types of chromosomes.
Living Environment Regents June 2010 Question 68 PDF Print E-mail
Monday, 30 May 2011 11:03

Diagram 1 cannot be used to know on confirm the evolutionary relationships of organisms. By merely looking at the stem cross sections, they may look the same. Just like in humans, some people may look the same but in truth they are not genetically related to each other. Thus, scientists are using genetic techniques such as gel electrophoresis which produces DNA profiles of organisms. Diagram 2 is an example of a DNA profile.

Last Updated on Monday, 30 May 2011 11:04
Living Environment Regents June 2010 Question 69 PDF Print E-mail
Monday, 30 May 2011 11:04

Diagram 3 is an example of a simplified cladogram. A cladogram is dichotomous phylogenetic tree that branches repeatedly, suggesting a classification of organisms based on the time sequence in which evolutionary branches. Each branch point is defined by synapomorphies or shared derived characters unique to the lineage that arises at that point. In Diagram 3, species A and B have shared characters which could be represented by the bands in Diagram 2 that appear on the same spot and with the similar thickness.

On the other hand, the ancestor of species A and B share a common character with species C but since it quite apart from the characteristics of  A and B, only few bands are common in the three species.
Living Environment Regents June 2010 Question 70 PDF Print E-mail
Monday, 30 May 2011 11:06

Correct answer: (2) separation of DNA fragments on the basis of size

Gel electrophoresis is a laboratory technique used to separate DNA fragments according to size as they move through the gel matrix using electricity. The DNA fragments are attracted towards the other end of the matrix, and the smaller molecules move faster than the large ones. This technique is used in DNA profiling to identify possible genetic relationships of organisms.

Incorrect answers:

(1) Synthesis of new DNA strands from subunits

Prior to electrophoresis, DNA fragments could be amplified using polymerase chain reaction (PCR). It is important to make copies of the DNA to help the researcher in other different molecular biology laboratory techniques.

(3) production of genetically engineered DNA molecules

Gel electrophoresis is only a molecular biology technique that may be used to know the presence of genes to be used for genetic engineering. It is not the process used to produce genetically engineered DNA. Instead, genetic engineering can be carried out through recombinant DNA technology.

(4) removal of defective genes from DNA

Gel electrophoresis is a process of classifying DNA molecules according to their sizes. It is not used for deletion of unwanted genes from the DNA. Unwanted genes can be "turned off" using genetic engineering techniques.

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