Mechanisms of Genetics

Where is the genetic code primarily located?

• Ribose sugars in RNA

• Phosphates in DNA

• Nucleotides in DNA

• Exons in RNA

Answer explanation

The genetic code is primarily located in the nucleotides of DNA, which consist of a sugar, phosphate, and a nitrogenous base. This sequence of nucleotides encodes the information necessary for protein synthesis.

What factor most directly determines the amino acids that are combined to create albumin?

• A) The temperature of the cell when translation is taking place

• B) The number of chromosomes in a cell

• C) The sequence of nucleotides in DNA

• D) The amount of energy that is available in the cell

Answer explanation

The amino acids in albumin are determined by the sequence of nucleotides in DNA, which encodes the genetic information necessary for protein synthesis. Thus, the correct answer is C.

What is the amino acid sequence that will be translated from the mRNA sequence?

• Threonine - Isoleucine - Serine - Tryptophan

• Cysteine - Tyrosine - Arginine - Threonine

• Serine - Methionine - Tyrosine - Tryptophan

• Proline - Arginine - Histidine - Arginine

Answer explanation

The mRNA sequence translates to amino acids based on codons. The correct choice, Cysteine - Tyrosine - Arginine - Threonine, corresponds to the specific codons in the mRNA, confirming it as the accurate translation.

A diagram of the steps in the production of a protein is shown. Which description identifies the purpose of Step A in this process?

• To correct mutations in the DNA sequence

• To produce an exact copy of the DNA molecule

• To copy the DNA of a gene sequence onto a strand of mRNA

• To assist in the folding of a protein.

Answer explanation

Step A's purpose is to copy the DNA of a gene sequence onto a strand of mRNA, a process known as transcription, which is essential for protein synthesis.

A DNA mutation results in a protein that is the same as the initial protein synthesized before the mutation. Which statement BEST explains this outcome?

• One amino acid substitution does not affect protein synthesis.

• Different codons can be translated into the same amino acid, so some mutations do not affect protein synthesis.

• Only mutations that occur at the chromosomal level change protein function.

• Amino acids have similar functions, so their corresponding proteins are unaffected by mutations.

Answer explanation

The correct choice is that different codons can code for the same amino acid, meaning some mutations are silent and do not change the protein's amino acid sequence, resulting in the same protein being synthesized.

Two mutations of a genetic sequence are shown. A DNA codon chart is also shown. Which mutation would have the MOST significant impact on the gene product?

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Answer explanation

The mutation that causes a frameshift or introduces a premature stop codon would have the most significant impact on the gene product, as it alters the entire amino acid sequence downstream, potentially leading to a nonfunctional protein.

Giraffes have 30 chromosomes in their somatic cells. How many chromosomes will each daughter cell have after the final step of meiosis?

Answer explanation

Giraffes have 30 chromosomes in somatic cells, which are diploid. During meiosis, the chromosome number is halved, resulting in daughter cells with 15 chromosomes each. Therefore, the correct answer is 15.

A cell undergoing a biological process is shown. Which process occurs between Step 2 and Step 3 and creates more genetic diversity in the resulting cells?

• Chromosome nondisjunction

• Genome replication

• Crossing over

• Chromosomal deletion

Answer explanation

Crossing over occurs during meiosis, where homologous chromosomes exchange genetic material, increasing genetic diversity in the resulting cells. This process is crucial for variation in offspring.

If both parents are heterozygous for both traits, what would be the genotype of an offspring with straight hair and the ability to taste PTC?

• HhPp

• hhPp

• Hhpp

• hhpp

Answer explanation

The offspring with straight hair (hh) must inherit the recessive allele from both parents. The ability to taste PTC (Pp) requires at least one dominant allele. Thus, the correct genotype is hhPp.

Cystic fibrosis is an autosomal recessive disorder in humans. What is the probability that an offspring will have cystic fibrosis if both parents are carriers of cystic fibrosis?

• A) 25%

• B) 50%

• C) 75%

• D) 100%

Answer explanation

Cystic fibrosis is autosomal recessive, meaning both parents must pass on the recessive allele for the child to have the disorder. If both are carriers (Cc), the Punnett square shows a 25% chance (cc) for the child to have cystic fibrosis.