Question

Inversion of DNA sequences within chromosomes is a common process in evolution. The following gene arrangements in a particular chromosome are found in four different species: First sequence: STUVWX Second sequence: UVXTSW Third sequence: UVWSTX Fourth sequence: SWVUTX Assuming that the arrangement in the first sequence is the ancestor/reference arrangement, in what evolutionary order did the four species arise, such that the fewest number of inversions occur between each species (place the first sequence as the earliest species in your ordering)2341

Answer 1

The species with different gene arrangements arose through a series of chromosome inversions from a common ancestral sequence, STUVWX. The most parsimonious evolutionary order of these species, given the fewest number of inversions, is first sequence (ancestor), fourth, second, and third. Chromosome inversions are a crucial evolutionary mechanism that also differentiates humans from chimpanzees.

Step-by-step explanation:

The question asks about the evolutionary order of species based on a hypothetical ancestral chromosome inversion sequence. The ancestral sequence given is STUVWX, and we must determine the most parsimonious order of inversions leading to the observed sequences in other species, UVXTSW, UVWSTX, and SWVUTX.

To minimize the number of inversions, we can compare each sequence with the ancestral sequence. Through comparison, the order that requires the fewest number of inversions is First sequence, Fourth sequence, Second sequence, and Third sequence. This order suggests that the fourth species arose first from the ancestral sequence with a two-step inversion (inverting UVW to WUV and then inverting the entire string), followed by the second species with one inversion of the middle segment (inverting TSW to SWT), and finally the third species diverges from the second with one final inversion of the middle segment (XTSW to WSTX).

Chromosome inversions are significant evolutionary mechanisms, as seen in the chromosome 18 inversion that differentiates humans from chimpanzees. A pericentric inversion in this chromosome, not found in chimpanzees, points to the importance of inversions in the evolution of new species, as differences in gene orientation can affect regulation and expression, potentially leading to varied traits within a population.

Answer 2

The correct answer is - 1, 4, 3, 2.

Step-by-step explanation:

It is given that the first sequence represents the earliest or ancestor species therefore, the first sequence would be - STUVWX

After the inversion, the highlighted sequence of the first sequence STUVWX gives rise to the second sequence as:

STUVWX

SWVUTX

Thus the second sequence after Ist inversion would be SWVUTX

2nd inversion, Third sequence:

SWVUTX

UVWSTX

Thus the third sequence after 2nd inversion is UVWSTX

3rd inversion, fourth sequence:

UVWSTX

UVXTSW

Thus, the fourth sequence after 3rd inversion is UVXTSW