What is Genetics & DNA on the Living Environment Regents?

Genetics & DNA is a Genetics topic on the Living Environment Regents. RegentsLab has 26 practice questions on it, each with a full worked solution.

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Genetics & DNA: Living Environment Regents Practice

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Question 17 · 2 pts

One strand of a DNA molecule has the base sequence $C\text{-}G\text{-}T\text{-}A\text{-}A\text{-}G$. According to the base-pairing rules, what is the sequence of bases on the complementary DNA strand?

(A) $C\text{-}G\text{-}T\text{-}A\text{-}A\text{-}G$
(B) $C\text{-}T\text{-}T\text{-}A\text{-}C\text{-}G$
(C) $G\text{-}C\text{-}A\text{-}U\text{-}U\text{-}C$
(D) $G\text{-}C\text{-}A\text{-}T\text{-}T\text{-}C$ ✓

Worked solution

$\text{Base-pairing rules: } A \text{ pairs with } T, \quad C \text{ pairs with } G$ In DNA, adenine always bonds with thymine and cytosine always bonds with guanine.

$C\to G,\ \ G\to C,\ \ T\to A,\ \ A\to T,\ \ A\to T,\ \ G\to C$ Pair each base of the given strand with its partner, keeping the same left-to-right order.

$\text{Complement} = G\text{-}C\text{-}A\text{-}T\text{-}T\text{-}C$ Read off the new strand in the same order as the original.

Answer: $G\text{-}C\text{-}A\text{-}T\text{-}T\text{-}C$

The two strands of DNA are complementary: adenine pairs with thymine and cytosine pairs with guanine, so the sequence of one strand determines the sequence of the other.

Question 18 · 2 pts

In a eukaryotic cell, which molecule carries the genetic instructions from the DNA in the nucleus to the ribosomes, where proteins are assembled?

(A) Messenger RNA (mRNA) ✓
(B) ATP
(C) Transfer RNA (tRNA)
(D) DNA

Worked solution

$\text{DNA (nucleus)} \to \text{mRNA}$ During transcription the DNA code is copied onto a strand of mRNA.

$\text{mRNA} \to \text{ribosome}$ The mRNA leaves the nucleus and carries the instructions to the ribosome for translation.

Answer: Messenger RNA (mRNA)

Because DNA stays in the nucleus, its code is copied onto mRNA, which carries the instructions to the ribosome where the protein is built.

Question 28 · 2 pts

Which statement about mutations is consistent with the modern understanding of genetics?

(A) Mutations never produce new inherited traits in a species.
(B) Every mutation is harmful to the organism in which it occurs.
(C) Only mutations that occur in sex cells (gametes) can be passed on to an organism's offspring. ✓
(D) Mutations that occur in body (somatic) cells are always inherited by offspring.

Worked solution

$\text{Mutation}=\text{a change in the DNA base sequence}$

$\text{Heritable only if it occurs in gametes (egg or sperm)}$ Somatic (body-cell) mutations are not passed on

$\text{Mutations may be harmful, neutral, or beneficial}$

Answer: Only mutations in sex cells (gametes) can be passed to offspring.

Mutations are random changes in DNA; only those occurring in egg or sperm cells are heritable, and they are an important source of genetic variation.

Question 32 · 2 pts

Two genetically identical tomato plants are grown from cuttings of the same parent. One is grown in full sunlight and the other in deep shade, and they reach very different heights. What does this observation best demonstrate?

(A) The two plants must carry different genes for height.
(B) Height is controlled entirely by genes and not by the environment.
(C) The shade permanently changed the DNA base sequence of one plant.
(D) An organism's characteristics are determined by both its genes and its environment. ✓

Worked solution

$\text{Same genes (identical plants)} + \text{different environments (sun vs shade)}$

$\to \text{different heights (different phenotypes)}$

$\text{Therefore the trait depends on genes AND environment}$

Answer: Characteristics are determined by both genes and the environment.

An organism's traits (phenotype) result from the interaction of its genetic information with environmental conditions, so identical genes can produce different traits in different environments.

Question 2 · 2 pts

A change in the base sequence of a gene that results from an error during DNA replication is best described as a

(A) cloning event
(B) recombination during fertilization
(C) mutation ✓
(D) differentiation

Worked solution

$A mutation is any change in the sequence of bases in DNA.$ definition

$Errors during DNA replication that are not corrected result in a permanent change in the base sequence, which is a mutation.$

Answer: mutation

Mutations are changes in the base sequence of DNA that can arise from copying errors during replication and may be passed on to offspring cells or organisms.

Question 51 · 4 pts · constructed response

In a species of pea plant, the allele for purple flowers (P) is dominant over the allele for white flowers (p). A heterozygous purple-flowered plant (Pp) is crossed with a white-flowered plant (pp). State the expected phenotype ratio of the offspring from this cross and explain how you determined this ratio using the alleles involved.

Model answer: The expected ratio is 1 purple : 1 white (50% purple, 50% white). This is because the Pp parent can donate either a P or a p allele, and the pp parent can only donate a p allele, giving offspring genotypes of Pp and pp in equal proportion; Pp is purple (P is dominant) and pp is white.

Worked solution

$Cross: Pp (purple) x pp (white)$ Set up the parental genotypes

$Gametes from Pp: P or p; gametes from pp: p only$ List possible gametes

$Offspring genotypes: Pp, Pp, pp, pp$ Combine gametes (Punnett square)

$Ratio: 1 Pp : 1 pp = 1 purple : 1 white$ Since P is dominant, Pp shows purple phenotype

Answer: The expected ratio is 1 purple : 1 white (50% purple, 50% white). This is because the Pp parent can donate either a P or a p allele, and the pp parent can only donate a p allele, giving offspring genotypes of Pp and pp in equal proportion; Pp is purple (P is dominant) and pp is white.

This is a monohybrid test cross; because one parent is homozygous recessive, the offspring ratio directly reflects the gametes produced by the heterozygous parent, giving a 1:1 phenotype ratio.

Question 20 · 1 pt

The process by which the information in a DNA molecule is used to assemble a protein follows which sequence?

(A) mRNA $\to$ DNA $\to$ protein
(B) protein $\to$ mRNA $\to$ DNA
(C) DNA $\to$ protein $\to$ mRNA
(D) DNA $\to$ mRNA $\to$ protein ✓

Worked solution

$\text{transcription: DNA} \to \text{mRNA}$ In the nucleus.

$\text{translation: mRNA} \to \text{protein}$ At the ribosome.

Answer: \text{DNA} \to \text{mRNA} \to \text{protein}

DNA is transcribed to messenger RNA, which is then translated by ribosomes into a sequence of amino acids, a protein.

Question 19 · 2 pts

Offspring produced by sexual reproduction usually show greater genetic variation than offspring produced by asexual reproduction. Which statement best explains why?

(A) Asexual reproduction causes mutations that never occur during sexual reproduction.
(B) Sexual reproduction combines genetic material from two parents, producing new combinations of genes. ✓
(C) Asexual reproduction uses meiosis to sort genes into new combinations.
(D) Sexual reproduction always produces a larger number of offspring.

Worked solution

$\text{Sexual: gametes from two parents unite}$ Two different parents each contribute genes through fertilization.

$\text{meiosis} + \text{fertilization} \to \text{new gene combinations}$ Sorting of genes during meiosis plus combining at fertilization creates variety.

$\text{Asexual: one parent} \to \text{identical offspring}$ One parent and mitosis produce offspring with little genetic variation.

Answer: Sexual reproduction combines genetic material from two parents, producing new combinations of genes.

Sexual reproduction mixes alleles from two parents through meiosis and fertilization, generating new gene combinations, while asexual reproduction copies a single parent's genes.

Question 20 · 2 pts

In order for a mutation to be passed on to an organism's offspring, in which type of cell must the mutation occur?

(A) A muscle cell
(B) A skin cell
(C) A nerve cell
(D) A sex cell (gamete) ✓

Worked solution

$\text{Offspring develop from gametes (sperm + egg)}$ Only sex cells contribute DNA to the next generation.

$\text{mutation in gamete} \to \text{can be inherited}$ A change in a sex cell can be passed to offspring.

$\text{mutation in body cell} \to \text{not inherited}$ Body-cell mutations affect only the individual in which they occur.

Answer: A sex cell (gamete)

Only sex cells pass DNA to the next generation, so only mutations in gametes can be inherited; mutations in body cells affect just the individual.

Question 21 · 2 pts

The sequence of bases in a gene directly determines the sequence of which subunits in the protein that the gene codes for?

(A) Fatty acids
(B) Amino acids ✓
(C) Nucleotides
(D) Simple sugars

Worked solution

$\text{gene (DNA bases)} \to \text{mRNA codons}$ The base sequence is transcribed into a sequence of mRNA codons.

$\text{each codon} \to \text{one amino acid}$ The ribosome reads each codon and adds a specific amino acid.

$\text{order of amino acids} \to \text{protein}$ Thus the order of bases sets the order of amino acids in the protein.

Answer: Amino acids

Proteins are chains of amino acids, and the order of bases in a gene specifies the order in which those amino acids are linked together.

Question 23 · 2 pts

During gel electrophoresis, an electric current moves fragments of DNA through a gel. The fragments are separated from one another based primarily on their...

(A) size (length of the fragments) ✓
(B) type of sugar they contain
(C) color
(D) number of chromosomes

Worked solution

$\text{DNA is negatively charged}$ When current is applied, DNA moves through the gel toward the positive electrode.

$\text{smaller fragments move farther}$ Short fragments pass through the gel more easily than long ones.

$\text{result: separation by fragment size}$ Fragments line up by length, forming a banding pattern.

Answer: size (length of the fragments)

In gel electrophoresis, negatively charged DNA fragments move through a gel and are sorted by length, with smaller fragments traveling farther from the wells.

Question 26 · 2 pts

A strand of DNA that serves as the template for transcription has the base sequence T-A-C-G-G-A. What is the base sequence of the mRNA strand transcribed from it?

(A) U-A-C-G-G-A
(B) A-U-G-C-C-U ✓
(C) T-A-C-G-G-A
(D) A-T-G-C-C-T

Worked solution

$\text{Transcription builds an mRNA strand complementary to the DNA template}$

$\text{A}\to\text{U},\ \text{T}\to\text{A},\ \text{C}\to\text{G},\ \text{G}\to\text{C}$ In RNA, uracil (U) replaces thymine (T)

$\text{T}\to\text{A},\ \text{A}\to\text{U},\ \text{C}\to\text{G},\ \text{G}\to\text{C},\ \text{G}\to\text{C},\ \text{A}\to\text{U}$

$\text{mRNA}=\text{A-U-G-C-C-U}$

Answer: The mRNA sequence is A-U-G-C-C-U.

During transcription, RNA polymerase assembles an mRNA strand whose bases are complementary to the DNA template, using uracil wherever the template has adenine.

Question 29 · 2 pts

Scientists insert the human gene for insulin into bacteria, and the bacteria then produce functional human insulin. What is the main reason this is possible?

(A) Insulin is composed of DNA rather than of protein.
(B) The genetic code is essentially universal, so bacteria can read the human gene and assemble the same protein. ✓
(C) Bacteria and humans belong to the same species.
(D) The ribosomes of the bacteria rewrite the human gene into a bacterial gene.

Worked solution

$\text{Human insulin gene (DNA)} \to \text{inserted into bacterial DNA}$

$\text{Bacteria transcribe and translate the gene} \to \text{human insulin}$

$\text{Works because the genetic code is shared by nearly all organisms}$ Universal genetic code / recombinant DNA

Answer: The genetic code is universal, so bacteria can read the human gene and make the protein.

Because nearly all organisms use the same DNA code and protein-making machinery, a human gene placed in bacteria directs production of the human protein through recombinant DNA technology.

Question 30 · 2 pts

Gel electrophoresis is used to separate fragments of DNA. On what basis are the fragments separated, and how do they move through the gel?

(A) By size, with smaller (shorter) fragments moving farther through the gel. ✓
(B) By color, with darker fragments moving farther.
(C) By the number of amino acids, with larger fragments moving farther.
(D) By size, with larger (longer) fragments moving farther through the gel.

Worked solution

$\text{Restriction enzymes cut DNA into fragments of different lengths}$

$\text{An electric field pulls the fragments through the gel}$

$\text{Shorter fragments travel farther; longer fragments stay near the start}$ Separation is by size

Answer: By size; smaller fragments move farther through the gel.

In gel electrophoresis an electric field pushes DNA fragments through a gel, so shorter fragments move faster and farther, separating the DNA by size for comparison such as DNA fingerprinting.

Question 31 · 2 pts

Offspring produced by sexual reproduction usually show more genetic variation than offspring produced by asexual reproduction. Which two processes are mainly responsible for this greater variation?

(A) Digestion and respiration, which provide energy for growth.
(B) DNA replication and mitosis, which make identical copies of each cell.
(C) Mitosis and cloning, which copy a single parent's genes exactly.
(D) Meiosis and fertilization, which shuffle and recombine genes from two parents. ✓

Worked solution

$\text{Meiosis} \to \text{gametes with new combinations of genes}$ Independent sorting and recombination

$\text{Fertilization} \to \text{combines genes from two different parents}$

$\text{Result: offspring genetically different from parents and from each other}$

Answer: Meiosis and fertilization.

Meiosis randomly sorts and recombines genes into gametes, and fertilization joins gametes from two parents, producing new gene combinations and greater variation.

Question 1 · 2 pts

A segment of a gene has the following sequence of bases on one strand of DNA: A-T-G-C-C-A. This sequence is used as a template to produce a strand of messenger RNA (mRNA). Which sequence of bases would be found in the mRNA molecule?

(A) U-A-C-G-G-T
(B) A-T-G-C-C-A
(C) U-A-C-G-G-U ✓
(D) T-A-C-G-G-T

Worked solution

$mRNA is synthesized as the complementary copy of the DNA template strand.$ transcription

$Base pairing rules: A pairs with U (not T) in RNA, T pairs with A, G pairs with C, C pairs with G.$ DNA to RNA pairing

$Template A-T-G-C-C-A becomes mRNA U-A-C-G-G-U.$

Answer: U-A-C-G-G-U

During transcription, mRNA is built as the complement of the DNA template strand, and RNA uses uracil (U) in place of thymine (T) wherever adenine appears on the template.

Question 14 · 2 pts

During DNA replication, an enzyme unwinds and separates the two strands of the double helix, and each original strand is then used as a template to build a new complementary strand. This process ensures that

(A) each new DNA molecule contains two newly made strands and no original strands
(B) RNA replaces DNA permanently in one of the two new molecules
(C) the two new DNA molecules are identical to each other but not to the original molecule
(D) each new DNA molecule contains one original strand and one newly made strand ✓

Worked solution

$DNA replication is semiconservative: the two original strands separate and each serves as a template.$ Key vocabulary

$Free nucleotides pair with the template strand by complementary base pairing (A-T, C-G).$ Base pairing rule

$Each resulting double helix therefore has one old (template) strand and one newly synthesized strand.$ Semiconservative result

$Both new molecules are identical copies of the original because complementary base pairing is precise.$ Accuracy of copying

Answer: each new DNA molecule contains one original strand and one newly made strand

DNA replication is semiconservative, meaning each new double helix is composed of one original template strand and one newly synthesized strand, which allows accurate copies of genetic information to be passed to new cells.

Question 19 · 2 pts

A change in the DNA sequence of a gene results in one amino acid being substituted for another in a protein. This altered protein no longer functions properly. This is an example of

(A) a gene mutation affecting protein structure and function ✓
(B) normal variation caused by meiosis with no effect on the organism
(C) an environmental change altering the organism's phenotype without changing DNA
(D) a change in the number of chromosomes in the cell

Worked solution

$A change in the DNA base sequence within a gene is called a gene (point) mutation.$ Definition

$The DNA sequence determines the mRNA codons, which determine the sequence of amino acids in a protein.$ Gene expression

$A substituted amino acid can change the shape of the protein, which can change or destroy its function.$ Structure-function link

$This scenario describes a mutation, not a chromosome number change or an environmental effect on phenotype alone.$ Elimination of distractors

Answer: a gene mutation affecting protein structure and function

Because DNA sequence determines amino acid sequence, a change in the DNA base sequence (a gene mutation) can substitute one amino acid for another, altering the protein's three-dimensional shape and its ability to function.

Question 25 · 1 pt

In pea plants, tall (T) is dominant over short (t). If two heterozygous tall plants (Tt × Tt) are crossed, what fraction of the offspring are expected to be short?

(A) $\tfrac{1}{2}$
(B) $\tfrac{3}{4}$
(C) $\tfrac{1}{4}$ ✓
(D) $0$

Worked solution

$Tt \times Tt \Rightarrow 1\,TT : 2\,Tt : 1\,tt$ Punnett square.

$tt = \tfrac14 \Rightarrow \text{short}$

Answer: \tfrac{1}{4}

A Tt × Tt cross gives a 3:1 tall:short ratio. Only the tt genotype (one of four boxes) shows the recessive short trait.

Question 22 · 2 pts

A single base in a gene is changed from one base to a different base. Which outcome is the most likely direct result of this change?

(A) A different amino acid may be placed in the protein, possibly changing the protein that is produced. ✓
(B) The ribosomes in the cell will be destroyed.
(C) The organism will always die.
(D) The number of chromosomes in the cell will increase.

Worked solution

$\text{base change} \to \text{possibly different codon}$ A new base can create a codon that calls for a different amino acid.

$\text{different amino acid} \to \text{altered protein}$ Changing one amino acid may change the protein's shape or function.

$\text{effect: harmful, helpful, or neutral}$ The result is not always harmful, so 'always die' cannot be correct.

Answer: A different amino acid may be placed in the protein, possibly changing the protein that is produced.

Because the order of bases codes for the order of amino acids, a base substitution can change an amino acid and therefore the protein, though the effect may be harmful, beneficial, or neutral.

Question 24 · 2 pts

Scientists can insert the human gene for insulin into bacteria, and the bacteria then produce human insulin. This is possible mainly because...

(A) bacteria and humans belong to the same species.
(B) the human gene is changed into a bacterial gene once it is inserted.
(C) the genetic code of DNA is essentially the same in all organisms, so bacteria can read and express the human gene. ✓
(D) bacteria reproduce sexually with human cells.

Worked solution

$\text{DNA code is (nearly) universal}$ The same bases and codons specify the same amino acids in almost all organisms.

$\text{human insulin gene} \to \text{bacterial DNA}$ The gene is inserted using recombinant DNA techniques.

$\text{bacteria read gene} \to \text{make human insulin}$ Because the code is shared, the bacterium translates the gene into the same protein.

Answer: The genetic code of DNA is essentially the same in all organisms, so bacteria can read and express the human gene.

Genetic engineering works because DNA's code is nearly universal, so a gene from one species can be expressed by another organism to make the same protein.

Question 25 · 2 pts

In a sample of double-stranded DNA, $22\%$ of the bases are thymine (T). Based on the base-pairing rules, what percentage of the bases are guanine (G)?

(A) 78%
(B) 28% ✓
(C) 56%
(D) 22%

Worked solution

$\text{A pairs with T and C pairs with G, so } \%A=\%T \text{ and } \%C=\%G$ Chargaff base-pairing rules

$\%T=22\% \Rightarrow \%A=22\%$ Adenine equals thymine

$\%A+\%T=22\%+22\%=44\%$

$\%G+\%C=100\%-44\%=56\%$

$\%G=\%C=\frac{56\%}{2}=28\%$

Answer: $28\%$ of the bases are guanine.

In double-stranded DNA adenine pairs with thymine and cytosine pairs with guanine, so $\%A=\%T$ and $\%C=\%G$, and the four percentages must total $100\%$.

Question 27 · 2 pts

During translation, a tRNA molecule has the anticodon U-A-C. To which mRNA codon will this anticodon bind?

(A) A-U-C
(B) U-A-C
(C) A-T-G
(D) A-U-G ✓

Worked solution

$\text{The anticodon binds the codon by complementary base pairing}$

$\text{U}\to\text{A},\ \text{A}\to\text{U},\ \text{C}\to\text{G}$ RNA-to-RNA pairing: A with U, C with G

$\text{codon}=\text{A-U-G}$

Answer: The anticodon U-A-C binds the codon A-U-G.

A tRNA anticodon pairs with the mRNA codon through complementary bases (A with U and C with G), so the anticodon UAC reads the codon AUG.

Question 3 · 2 pts

During meiosis in a human cell, homologous chromosomes separate and are distributed independently into gametes. This process, along with crossing-over, most directly contributes to

(A) an increase in the chromosome number of offspring
(B) genetic variation among offspring ✓
(C) identical gametes being produced by one parent
(D) asexual reproduction in humans

Worked solution

$Meiosis produces gametes with half the chromosome number through two divisions.$ reduction division

$Independent assortment of homologous chromosome pairs and crossing-over between homologs shuffle allele combinations.$

$This shuffling produces gametes with new combinations of alleles, increasing genetic variation among offspring.$

Answer: genetic variation among offspring

Independent assortment and crossing-over during meiosis rearrange parental alleles into new combinations in gametes, which is a major source of genetic variation in sexually reproducing organisms.

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