SAT II Biology M : Genes and Chromosomes

Study concepts, example questions & explanations for SAT II Biology M

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Example Questions

Example Question #1 : Genes And Chromosomes

A diploid cell has two sets of chromosomes, what is the diploid number for a human somatic cell if one human gamete has 23 chromosomes?

Possible Answers:

69

48

36

44

46

Correct answer:

46

Explanation:

A gamete will have n=23 chromosomes while a somatic cell is going to have a diploid number of cells, or 2n=46. This is the case because somatic cells are going to receive a copy of chromosomes from each parent, so 23 from the mother and 23 form the father to give 46 total chromosomes. If you are ever given the haploid number and asked for the diploid number, then you can simply double the haploid number.

Example Question #2 : Genes And Chromosomes

During which of the following phases of the cell cycle does duplication of the genetic material occur?

Possible Answers:

Anaphase

G2

S

G1

Metaphase

Correct answer:

S

Explanation:

The correct answer is the "S," or synthesis, phase. The cell cycle consists of six main parts: interphase, prophase, metaphase, anaphase, telophase, and cytokinesis. Interphase, the longest part of the cell cycle, is subdivided into three different phases: G1, S, and G2. G1 comes first; in this phase, the cell simply grows. In the S phase, the cell synthesizes (creates) a new set of DNA using its original genome as a template. In G2, the cell (which now contains two copies of DNA) continues to grow. These growth phases are an important part of interphase because the cell must grow enough to have enough cytoplasm to give to each of its daughter cells at the end of mitosis or meiosis.

Example Question #3 : Genes And Chromosomes

Which of the following represents a phenotype?

Possible Answers:

Autosomal dominant

X-linked recessive

Brown hair

Aa

5'GATACGG3'

Correct answer:

Brown hair

Explanation:

A phenotype is a physical trait that can be observed. Thus, eye color (and hair color) are great examples of phenotypes. A genotype describes the genetic traits of a person (e.g. whether that person has the autosomal or recessive alleles of a gene). The genotype of an individual determines his or her phenotype.

Example Question #4 : Genes And Chromosomes

Each person can have one of four possible blood types: A, B, AB, or O. Blood type A means that the "A" antigen is present on the red blood cell surface. Blood type B means that the "B" antigen is present on red blood cells' surfaces. Blood type "AB" means that both the "A" antigen and the "B" antigen are present on the red blood cells' surfaces. Blood type "O" means that no antigens are present on the red blood cells' surfaces.

Someone with genotype "A/A" or "A/O" will have type A blood. Someone with genotype "B/B" or "B/O" will have type B blood. Someone with genotype "A/B" will have AB blood, and someone with genotype "O/O" will have type O blood.

Assume that blood type is not a sex-linked trait. A mother with genotype "A/O" and a father with genotype "A/B" could NOT have a child with which blood type?

Possible Answers:

O

A

Not enough information

AB

B

Correct answer:

O

Explanation:

The easiest way to solve this problem is to draw a punnet square. The genotypes of the parents are "AO" and "AB". The potential genotypes of their children are "AA", "AO", "BA", and "BO". Children with genotypes "AA" and "AO" will have type A blood. Children with genotype "BO" will have type B blood. Children with genotype "BA" will have type AB blood. Genotype "O/O" is the only one that will result in type O blood. "O/O" is not a possible product of this punnet square. Both the mother and the father must have the "O" allele in order for a child to have genotype "O/O" and type O blood.

Example Question #5 : Genes And Chromosomes

The genetic underpinnings of a disease have recently been identified. This disease has been found to result from a single point mutation in the coding sequence of a gene. The normal coding sequence of this gene is 5' - GATTACG - 3'. Which of the following could be the disease-causing form of the gene?

Possible Answers:

5' - GCATTAG - 3'

5' - GATCACG - 3'

5' - GATTTACG - 3'

5' - GATGATACG - 3'

5' - CGTAATC - 3'

Correct answer:

5' - GATCACG - 3'

Explanation:

This question is essentially asking, "Which of the following is a point mutation of the original sequence?" A point mutation is a mutation in which one base pair of DNA is substituted for another. A point mutation will not change the reading frame of a DNA sequence because it does not involve adding or removing any bases. The only answer choice that is identical to the original sequence with the exception of one base pair being changed for another is 5'GATCACG3', so this is the correct answer.

Example Question #6 : Genes And Chromosomes

A sample of RNA is sequenced and found to contain  adenine. Which of the following conclusions can also be drawn about the sample?

Possible Answers:

The sample contains  uracil.

The sample contains  thymine.

The sample contains  thymine.

The sample contains  uracil.

The sample contains  cytosine.

Correct answer:

The sample contains  uracil.

Explanation:

In RNA, the nucleic acid base adenine pairs with uracil. (In DNA, it pairs with thymine). In both RNA and DNA, cytosine pairs with guanine. Accordingly, RNA will have the same percent uracil as it does adenine—in this case, .  

(In this case it will also contain  guanine and  percent cytosine, because the adenine and uracil together add up to  and the remaining  is divided evenly between the paired guanine and cytosine (and  divided by two is ).

Example Question #7 : Genes And Chromosomes

If one of an organism's gametes contains 16 chromosomes, how many chromosomes will one of its somatic cells contain?

Possible Answers:

Correct answer:

Explanation:

Gametes are germ cells used in sexual reproduction, such as eggs or sperm. They are haploid cells with a chromosome number of , while somatic (non-reproductive) cells are diploid with a chromosome number of So, if an organism's gametes have  chromosomes each, a somatic cell in that organism will have twice that number of chromosomes—in this case, .

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