Which of the following are sources of genetic variability?

• A. Independent assortment
• B. Crossing over
• C. Random fertilization
• D. All of the above

Answer: (D)

Genetic variability comes from processes that shuffle existing alleles into new combinations. Independent assortment during meiosis I causes maternal and paternal chromosomes to sort into gametes in many different ways, producing diverse allele combinations. Crossing over in prophase I exchanges segments between homologous chromosomes, creating chromosomes with new allele arrangements. Random fertilization means any sperm can fuse with any egg, dramatically increasing the number of possible offspring genotypes. Together, these mechanisms generate the variety of genetic possibilities that selection can act upon.