Which of the following cellular processes would most likely lead to increased genetic diversity in a population of organisms?

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11ecba2d_0fd9_81ba_a3bf_6b0689ec747e_MD0008_00 In eukaryotes, reproductive cells (gametes) are produced via meiosis, during which a parent cell (2n) divides to produce four genetically distinct daughter cells containing half the original number of chromosomes (n). Meiosis has four phases (like mitosis), but these phases occur in two successive cell division stages (meiosis I and II). In prophase I of meiosis, homologous chromosomes recognize each other and line up side by side during synapsis. Because each homologous chromosome consists of two identical (sister) chromatids, this adjacent chromosomal alignment forms a tetrad (four chromatids total). Tetrads arise when a synaptonemal complex (protein structure) forms between homologous chromosomes and holds them together tightly. The tetrad structure allows physical contact between the paternal and maternal chromosomes at the chiasma, a point where a chromosome segment can break off and rejoin with the opposite homologous chromosome. This exchange of DNA is the hallmark feature of the process called crossing over. Crossover events result in daughter cells with chromosomes containing combinations of alleles that differ from those in the parent cell, leading to eukaryotic genetic recombination and increased genetic diversity. Because crossover events produce genetically unique gametes, the offspring that develops after fertilization is genetically different from either parent and more genetically diverse. (Choice A) DNA replication does not involve the exchange of genetic information seen during crossing over in meiosis. DNA replication (synthesis) occurs during the S phase of the cell cycle and precedes mitosis. (Choice C) In alternative splicing, a single gene transcript is processed to produce various mRNA molecules that encode different proteins, depending on the inclusion or exclusion of particular exons. Alternative splicing can increase protein diversity, but it does not increase genetic diversity as the genetic makeup of an offspring is not altered. (Choice D) Mitosis is the process by which a cell divides to create two genetically identical daughter cells. However, during mitosis, homologous chromosomes do not pair up into tetrads and crossing over does not occur. Educational objective: In eukaryotes, genetic recombination occurs via crossover events (exchange of DNA segments between homologous chromosomes). Synapsis or the joining of homologous chromosomes into tetrads occurs during prophase I of meiosis and is required for crossing over to occur. Crossovers increase genetic diversity by mixing maternal and paternal alleles into a single chromosome that is then inherited by the offspring.

Which of the Following Cellular Processes Would Most Likely Lead