Which of the following occurs in all species of living organisms and may lead to an increase in genetic variation?

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Question restatement: Which of the following occurs in all species of living organisms and may lead to an increase in genetic variation?

Option 1: Alternative splicing of mRNA. This process expands protein diversity in many organisms, but not all species rely on or express alternative splicing to the same extent. Some organisms have limited or no alternative splicing, so it does not universally occur across all life.

Option 2: Crossing-over in meiosis. While this is a major source of genetic recombination in sexually reproducing organisms, many species reproduce asexually or may have variations in meiotic processes. Therefore, crossing-over is not guaranteed to occur in all species.

Option 3: Random assortment of chromosomes. This is another mechanism tied to meiosis and the segregation of homologous chromosomes, which again is not a universal feature across all organisms, particularly those with asexual reproduction or unusual chromosome behavior.

Option 4: Mutations in the genome. Mutations are fundamental genetic changes that can arise spontaneously in any organism with DNA (or RNA genomes with replication errors) and are a universal source of genetic variation. Although not every mutation increases variation (many are neutral or deleterious), the potential for mutation exists in all species and can lead to increased variation over generations.

Why Option 4 is the best fit: Since the question asks for something that occurs in all species and may increase genetic variation, mutations fulfill both criteria: they occur universally and they can introduce new alleles or variations in populations, driving genetic diversity over time.

Why the other options are not universally applicable:
- Alternative splicing is common in eukaryotes but not guaranteed to occur in all species, and some organisms may have minimal or no evidence of this process.
- Crossing-over in meiosis is limited to organisms undergoing sexual reproduction and meiosis; many species reproduce asexually and do not experience meiotic recombination.
- Random assortment of chromosomes is a product of meiosis and is contingent on the presence of homologous pairs and meiotic division, which is not universal across all species.

Result overview (without declaring the answer): Each option indicates a mechanism that can contribute to genetic variation under certain conditions, but only one is a universal process with the potential to increase variation across all living species, namely mutations in the genome.

APBIO141-031 with labs S15 - CollegeBoard* AP Exam Prep: Multiple Choice

Which of the following occurs in all species of living organisms and may lead to an increase in genetic variation?

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