Evolution and Mutations - GRE

Convergent evolution is the phenomenon by which two separate species evolve a shared trait. A classic example of this is that both birds and bats have evolved wings, but do not share a common ancestor prior to the development of this trait. Birds and bats developed their wings separately through completely unique mechanisms.

A population diverging into two separate species while residing in the same area describes the phenomenon of sympatric speciation. A species regaining a trait is an example of evolutionary reversal.

Convergent evolution is the phenomenon by which two species independently evolve a similar trait. An excellent example is the evolution of flight/wings in birds and bats, which do not share a common ancestor. Parsimony is a principle that guides scientific explanation toward simple terms, rather than eleborate principles. By parsimonious thinking, the simplest explanation is also the most likely to be true. Artificial selection is a form of evolution in which organisms are selected and bred for beneficial traits that would not necessarily be selected for in nature. Dog breeding and the production of numerous types of produce and grains are subject to artificial selection by humans (this is different from genetic modification).

Divergent evolution describes the accumulation of distinct traits that can lead to speciation events. A large population consists of a single ancestor species. Over time, different groups of the population come to inhabit different niches and develop traits for specialized inhabitance of that niche. As these changes accumulate, the population slowly develops distinct groups. When these groups can no longer reproduce due to some sexual barrier, a speciation event has occurred. This process aligns with the theory of evolution for Darwin's finches.

While a missense mutation involves substituting a base pair, resulting in a new amino acid, a nonsense mutation takes place when the new substituted codon is a stop codon. This causes the protein to stop being translated prematurely. Because of their impact on protein production, nonsense mutations very commonly prevent the formation of a functional protein.

Silent mutations result in no change in primary protein structure. Due to the degeneracy of the genetic code, a mutation can occur without changing the identity of the amino acid recruited during translation. A frameshift mutation results in a shift in the codon reading frame, severely altering the primary protein structure and often resulting in a truncated protein.

Nonsense mutations are the name specifically given to mutations that cause the ribosome to encounter a premature stop codon and terminate translation early. A point mutation causes the transcription of a stop codon by changing the DNA transcript transcribe to the mRNA stop codons UAG, UAA, or UGA. Placement of this codon in the transcript will interrupt translation.

Missense mutations are a type of mutation that result in the inclusion of a different amino acid than the wild type protein. Frameshift mutations result in a change to the codon reading frame, and are typically caused by deletion or insertion mutations. Frameshift mutations have the most dramatic and detrimental effect on proteins. Deletion mutations result from removal of one or more base pairs.

When only one amino acid is changed in a polypeptide, it is commonly caused by a point mutation, where one base pair has been changed. Silent, missense, and nonsense mutations can all be caused by a point mutation. Since the amino acid sequence has been changed, this is an example of a missense mutation. A silent mutation would not change the amino acid sequence, and a nonsense mutation would result in a premature stop codon during translation.

The higher the taxonomic group, the less similar the members are. This is true for appearance, behavior, and genetics. The order of taxonomic groupings, from most general to most specific is: kingdom, phylum, class, order, family, genus, species.

Of the given answers, phyla are the highest taxonomic rank. Species of different phyla would show the greatest genetic difference. In contrast, genera are the lowest taxonomic rank of the given answers; species of the same genus would show the least genetic difference.

Cell walls were present in plant cells before the transition to land. Seeds, stomata, waxy cuticles, and vascular transport all evolved to reduce water loss and circulate water to all areas of the plant. Water loss and circulation were not an issue before the transition to land; plants were forced to adapt these traits in order to survive in a terrestrial environment.

Swimming sperm is a feature of avascular and early vascular plants, who needed to remain in moist environments in order to retain water.

After gaining vascular systems, plants were able to circulate water and nutrients more efficiently, thus being able to grow larger, have more leaves, develop branched systems of roots and shoots to collect water and nutrients, and better dispersal of spores due to gains in size.

Thylakoid membranes are found within chloroplasts, which are used for photosynthesis. Plants found in both aquatic and terrestrial environments photosynthesize, so these membranes cannot be considered adaptations uniquely benefiting terrestrial plants.

Comparatively, cutin is a waxy coating found on various parts of plants that helps prevent water loss when exposed to air. Stomata are tiny openings in the epidermis of plants that allow for the exchange of carbon dioxide and oxygen while minimizing water loss. Roots and root hairs allow plants to absorb nutrients and water from the soil. Water loss was the primary challenge plants faced when moving from aquatic to terrestrial environments; cutin, stomata, roots, and root hairs all help terrestrial plants absorb and conserve water.

Plants developed more rigid structures to help maintain their growth on land as opposed to water.

Waxy cuticles developed to help reduce water loss/desiccation. Roots allowed plants greater access to water, as well as provided anchoring to the ground; this allowed plants to grow taller. Vascular tissue facilitated transport of water and nutrients to all parts of the plant. Stomata helped with gas exchange.

The correct answer is polymorphism. A polymorphism refers to multiple phenoytpes (morphs) that exist within a population, generally as a result of multiple alleles for the same gene.

Sympatry and allopatry refer to mechanisms of speciation and natural selection favors a certain phenotype for its fitness or other survival advantages. Assortative mating describes a biased mating pattern based on either phenotype or behavior.

In order for a nucleotide substitution to be considered a SNP and not a random mutation, it must occur in 1% or more of the population. SNPs are more frequently found in non-coding regions. Typically, SNPs are much less commonly found in AT-rich microsatellites.

If single nucleotide polymorphisms (SNPs) that occur in coding regions do not trigger an amino acid change in the protein, they are synonymous. A SNP can cause a missense mutation (an amino acid change in the protein) or a nonsense mutation (an amino acid change to a stop codon), both of these are nonsynonymous substitutions.

Plants developed more rigid structures to help maintain their growth on land as opposed to water.

Waxy cuticles developed to help reduce water loss/desiccation. Roots allowed plants greater access to water, as well as provided anchoring to the ground; this allowed plants to grow taller. Vascular tissue facilitated transport of water and nutrients to all parts of the plant. Stomata helped with gas exchange.

Cell walls were present in plant cells before the transition to land. Seeds, stomata, waxy cuticles, and vascular transport all evolved to reduce water loss and circulate water to all areas of the plant. Water loss and circulation were not an issue before the transition to land; plants were forced to adapt these traits in order to survive in a terrestrial environment.

Swimming sperm is a feature of avascular and early vascular plants, who needed to remain in moist environments in order to retain water.

After gaining vascular systems, plants were able to circulate water and nutrients more efficiently, thus being able to grow larger, have more leaves, develop branched systems of roots and shoots to collect water and nutrients, and better dispersal of spores due to gains in size.

Thylakoid membranes are found within chloroplasts, which are used for photosynthesis. Plants found in both aquatic and terrestrial environments photosynthesize, so these membranes cannot be considered adaptations uniquely benefiting terrestrial plants.

Comparatively, cutin is a waxy coating found on various parts of plants that helps prevent water loss when exposed to air. Stomata are tiny openings in the epidermis of plants that allow for the exchange of carbon dioxide and oxygen while minimizing water loss. Roots and root hairs allow plants to absorb nutrients and water from the soil. Water loss was the primary challenge plants faced when moving from aquatic to terrestrial environments; cutin, stomata, roots, and root hairs all help terrestrial plants absorb and conserve water.

Mitochondrial DNA (mtDNA) is only inherited directly from a mother to her offspring and can be used to directly track lineage of a population or species. Nuclear DNA (nDNA) is inherited from both the father and mother of the offspring; it can be used to track lineage as well, but mtDNA similarity is enough to conclude a close relationship between the two populations described in the question.

Color, diet, and location are all distinguishing features of the populations and help characterize their niche in the ecosystem. Diet and location (territory) are not heritable traits, and do not signify ancestry. Color is genetic, but could result from convergent or divergent evolution. mtDNA similarity is the strongest available evidence for a close ancestral link between populations A and B.

In order to derive an accurate estimate of phylogenetic relationships, scientists need to use neutral DNA markers in their studies. If genes are under any sort of selection, it could completely change the results, because this may not reflect the actual evolutionary past of the organisms. It is also generally important to incorporate both nuclear and mitochondrial DNA, because these types of genes can show different histories (remember, mitochondrial DNA is inherited maternally).

Mitochondrial DNA (mtDNA) is only inherited directly from a mother to her offspring and can be used to directly track lineage of a population or species. Nuclear DNA (nDNA) is inherited from both the father and mother of the offspring; it can be used to track lineage as well, but mtDNA similarity is enough to conclude a close relationship between the two populations described in the question.

Color, diet, and location are all distinguishing features of the populations and help characterize their niche in the ecosystem. Diet and location (territory) are not heritable traits, and do not signify ancestry. Color is genetic, but could result from convergent or divergent evolution. mtDNA similarity is the strongest available evidence for a close ancestral link between populations A and B.