Which of the following contributes to genetic variation in sexually reproducing species?

• A. Crossing over, internal fertilization, independent assortment
• B. Independent assortment, spindle formation, random fertilization
• C. Random fertilization, DNA synthesis, independent assortment
• D. Internal fertilization, spindle formation, crossing over
• E. Random fertilization, independent assortment, crossing over

Answer: (E)

Verified step by step guidance

1. Understand that genetic variation in sexually reproducing species is primarily introduced through three main mechanisms: crossing over, independent assortment, and random fertilization.
2. Crossing over occurs during prophase I of meiosis, where homologous chromosomes exchange genetic material, leading to new combinations of alleles.
3. Independent assortment refers to the random distribution of maternal and paternal chromosomes into gametes during metaphase I of meiosis, resulting in a variety of genetic combinations.
4. Random fertilization adds to genetic variation because any sperm can fertilize any egg, leading to a unique combination of genes in the offspring.
5. Evaluate the options given in the problem and identify the one that includes all three mechanisms: random fertilization, independent assortment, and crossing over.