The trait is recessive because affected individuals do not occur in every generation. Additionally, dominant traits do not result in "carriers". Individuals are either affected or unaffected.

The best answer is a nonsense mutation, which is defined as a point mutation that gives rise to an early stop codon, thus truncating any protein products prematurely. These are typically devastating mutations for protein function.

The beta cell-specific Dia mutation in group C causes results similar to the global Dia mutation in group B. From this, we can conclude that Dia is functioning within the beta cells. Essentially, deleting Dia from the beta-cells is equivalent to deleting it from the entire body. Additionally, loss of Dia in skeletal muscle in group D seems to have no phenotypic effect, indicating that Dia is not necessary in skeletal muscle.

Pancreatic beta cells are responsible for insulin production, while skeletal muscle plays a significant role in insulin sensitivity. Since loss of Dia in beta cells leads to high blood glucose, we can conclude that the role of Dia is in the promoting the production of insulin, and that the gene plays no role in insulin sensitivity.

The question informs us that the mutational defect in the gene involves the enzyme's ability to load copper onto apoceruloplasmin. Healthy individuals are able to load copper to apoceruloplasmin, creating serum-soluble ceruloplasmin. With this process disrupted in an individual with Wilson's Disease, we would expect that less ceruloplasmin would be produced because copper could not be transported. We would expect to see reduced serum levels of the complete protein, and high levels of copper building up in hepatocytes and circulatory serum.

Recessive alleles are often created by mutated versions of functional genes that encode broken/nonfunctional proteins. The question is thus asking us which of the mutations is likely to result in a nonfunctional or abnormal protein.

Silent mutations are types of mutations that result in the insertion of the same amino acid due to the degeneracy of the genetic code and, therefore, will not cause any noticeable change in the protein. Essentially, even organisms with the mutation will still show the dominant allele.

Frameshift mutations change the reading frame used for translation and oftentimes result in premature stop codons. Nonsense mutations are mutations that specifically result in premature stop codons and generally result in nonfunctional proteins. Missense mutations lead to the insertion of a different amino acid at the normal site. This can lead to serious problems for the functionality of the protein, particularly if the mutation is present in the active site or another area that is highly conserved throughout evolution.

A framshift mutation is when an extra base is inserted into (or deleted from) a strand of DNA. When the DNA is transcribed, every codon downstream from the insertion is changed because the reading frame will be different. This will be the case for any mutations that affect a sequence of nucleotides that is not a multiple of three, for example a five-nucleotide deletion. Such mutations affect the three-nucleotide groupings for all codons following the mutation, and often result in a premature stop codon.

The correct answer is CGGTGAATAGGC  CGGTGAATCAGGC. In the original sequence, the codons are CGG-TGA-ATA-GGC. In the second, they become CGG-TGA-ATC-AGG-C. The other answers show either insertions or deletions that do not shift the reading frame, or single nucleotide polymorphism (changing a single nucleotide to another).

Note that the reading frame does not change in the following 3-nucleotide insertion. Though there is an extra codon, the downstream sequence is not affected.

CGG-TGA-ATA-GGC  CGG-TGA-AGA-CTA-GGC

A missense mutation is the substitution of one nucleotide for another in the DNA sequence, resulting in a different resulting amino acid. Essentially, one amino acid is replaced with another. This type of mutation will not alter the overall protein length.

A nonsense mutation results in a pre-mature stop codon, causing early termination of the protein product and a shorter protein. Frameshift mutations commonly cause pre-mature stop codons to arise, and at the very least will result in a highly altered protein product that is likely of a different length from the unaltered protein. Single-base addition and deletions will cause frameshift mutations.

Healthy RNA: 3'-AGG-UCG-UUA-GUC-5'

Missense:     3'-AAG-UCG-UUA-GUC-5'

Nonsense:    3'-AGG-UAG-5' (UAG stop codon)

Frameshift:   3'-AAG-GUC-GUU-AGU-C-5' (single-base addition)

Framshift:     3'-AGU-CGU-UAG-5' (single-base deletion, UAG stop codon)

Since the maternal oocyte would have two copies of chromosome 21, the normal 21 and the derivative chromosome, the normal addition of the sperm would lead to a zygote with a total of three copies of chromosome 21, or trisomy 21. Polyploidy is a tempting choice, but polyploid is a state characterized by extra copies of multiple chromosomes, as might be expected from more than one sperm fertilizing an egg.

First, you want to narrow down the answers to those with the fewest changes (1 base change). Next, you needed to select the single base change on the third base of the codon. A silent mutation (a DNA mutation that doesn't result in an amino acid change) is most likely to occur when the third base of a codon is changed.

Original sequence: 5'-CGA TGA ACG-3'

Unaltered mRNA transcript: 3'-GCU ACU UGC-5'

Note that the mRNA sequence is antiparallel, changing the orientation of the codons. mRNA is read in the 5'-to-3' direction by the ribosome, meaning that the third base in the codon will be to the left of the 3-base sequence. The given RNA sequence will be read as CGU UCA UCG.

Correct answer: 5'-CGA CGA ACG-3'

Altered mRNA transcript: 3'-GCU GCU UGC-5'

The sequence will be read as CGU UCG UCG.

The correct answer involves a mutation in the third nitrogenous base of the second codon. Both UCA (original) and UCG (altered) code for serine.

A silent mutation is a mutation that results in the inclusion of the same amino acid in the polypeptide product, despite a change in the DNA template sequence. Silent mutations generally involve the third nucleotide in the codon sequence, since this unit is often interchangeable due to the degeneracy of the coding sequence.

A missense mutation results in a different amino acid inclusion based on codon alteration. A nonsense mutation is the insertion of a new stop codon as a result of mutation, resulting in a truncated polypeptide and severely hindering functionality. An insertion or frameshift mutation can change the reading frame of the mRNA template, drastically changing the identity and primary sequence of the polypeptide product; these are the most dangerous type of mutation, as the product may be harmful as well as nonfunctional.