Question

down syndrome, the most common genetic condition in the united states, is also called trisomy 21. what does this mean?
a) a person with down syndrome has three copies of chromosome 21 instead of two copies. two sperm cells simultaneously fertilized the egg cell.
b) a person with down syndrome has only one copy of chromosome 21 instead of two copies. either the sperm cell or the egg cell was lacking this chromosome.
c) a person with down syndrome has two copies of chromosome 21 but theyre fused together. during early embryo development, these chromosomes didnt segregate properly.
d) a person with down syndrome has three copies of chromosome 21 instead of two copies. an extra chromosome 21 was present in either the sperm or the egg cell.

question 6 (5 points)
listen
why are well-defined reading frames critical in protein synthesis?
a) without a well-defined reading frame, the resulting protein would be transported to the cell surface.
b) without a well-defined reading frame, the ribosome is unable to bind to the mrna.

Explanation:

First Question (About Down Syndrome)

• Down syndrome (trisomy 21) is caused by an extra copy of chromosome 21. Option A's "two sperm cells fertilizing" is incorrect (fertilization by two sperms is polyspermy, not trisomy). Option B describes monosomy (one copy), not trisomy. Option C's "fused chromosomes" is not the cause of trisomy 21; trisomy is due to an extra chromosome from a gamete (sperm/egg) with an extra 21st chromosome. Option D correctly explains trisomy 21 as three copies (due to an extra chromosome in sperm or egg).

Second Question (About Reading Frames in Protein Synthesis)

(Note: The options provided seem incomplete, but assuming typical knowledge about reading frames: A well - defined reading frame is critical because it determines how the mRNA codons are read (in groups of three) to code for amino acids. Without a proper reading frame, the codons would be misread, leading to a completely different (or non - functional) amino acid sequence. Let's analyze the given options:

• Option A: Transport to the cell surface is not related to the reading frame's role in protein synthesis. The reading frame is about codon reading for amino acid sequence, not protein transport.
• Option B: Ribosome binding to mRNA is related to the ribosome - mRNA interaction (e.g., ribosome binding site), not the reading frame. The reading frame is established after ribosome binding and is about codon translation.

If we assume there are more options (e.g., one about correct amino acid sequence), but with the given options, both A and B are incorrect. However, since the question is incomplete, we can only analyze the given ones. If we had to choose between A and B based on the given, both are wrong. But if we consider standard knowledge, the correct reason (not in given options) is that the reading frame determines the correct sequence of amino acids; without it, the codons are misread, and the protein's amino acid sequence (and thus function) is altered. )

• Option A: The reading frame has no direct relation to protein transport to the cell surface. Protein transport is governed by other cellular mechanisms (e.g., signal peptides, vesicular transport), not the reading frame.
• Option B: Ribosome binding to mRNA is mediated by sequences like the ribosome binding site (in prokaryotes) or the 5' cap (in eukaryotes), not the reading frame. The reading frame is about how the ribosome reads the codons after binding.

Answer:

D) A person with Down syndrome has three copies of chromosome 21 instead of two copies. An extra chromosome 21 was present in either the sperm or the egg cell.