What is the process called when chromosomes physically exchange parts?

The process in which chromosomes physically exchange parts is known as crossing over. This occurs during meiosis, specifically during prophase I, when homologous chromosomes pair up and exchange segments of their genetic material. This genetic recombination increases genetic diversity in the resulting gametes, contributing to variability in offspring.

Crossing over is a critical mechanism in the process of evolution and helps maintain the genetic health of a population by allowing for new combinations of alleles. This process is essential for the adaptation and evolution of species, as it generates genetic variation that can be acted upon by natural selection.

The other options, while related to genetics and evolution, refer to different concepts. Gene migration typically pertains to the movement of genes between populations, genetic drift refers to random changes in allele frequencies in a population, and gene flow involves the transfer of genetic variation from one population to another. These processes contribute to evolution and population dynamics but do not involve the physical exchange of chromosome parts.