Question

Which of the following statements is true regarding homology and homologous sequences.

a)If two sequences are homologs then they are also paralogs

b)If two sequences are homologs then they are also orthologs

c)If two sequences can be aligned via a sequence alingment then they are homologs.

d)Suppose tha there are n differences between two sequences ,and that the probability of this ocurring at random is less than 0.05.Then the sequences are homologs.

e)All of the above

f)None of the above

Answer 1

A) Homologous sequences are paralogous if they were separated by a gene duplication event: if a gene in an organism is duplicated to occupy two different positions in the same genome, then the two copies are paralogous. Paralogs typically have the same or similar function, but sometimes do not.

B) Homologs are considered orthologs if they have identical functions (or more narrowly, if they share a particular function of interest); if their functions have diverged (or narrowly, if one has the function of interest and the other does not), they are considered paralogs.

Both orthologs and paralogs are types of homologs, that is, they denote genes that derive from the same ancestral sequence. Orthologs are corresponding genes in different lineages and are a result of speciation, whereas paralogs result from a gene duplication.

C) Homologous sequences do not always share significant sequence similarity; there are thousands of homologous protein alignments that are not significant, but are clearly homologous based on statistically significant structural similarity or strong sequence similarity to an intermediate sequence. Thus, when a similarity search finds a statistically significant match, we can confidently infer that the two sequences are homologous.

Therefore option (E) is correct.