Homologous chromosomes are chromosome pairs of the same length, centromere position, and staining pattern, with genes for the same characteristics at corresponding loci. One homologouschromosome is inherited from the organisms mother; the other from the organism’s father. They pair (synapse) during meiosis, or cell division that occurs as part of the creation of gametes.
Each chromosome pair contains genes for the same biological features, such as eye color, at the same locations (loci) on the chromosome. Each pair, however, can contain the same allele (both alleles for blue eyes) or different alleles (one allele for blue eyes and one allele for brown eyes) for each feature.
Chromosomal crossover (or crossing over) is an exchange of genetic material between homologous chromosomes. It is one of the final phases of genetic recombination, which occurs during prophase I of meiosis (pachytene) in a process called synapsis. Synapsis begins before the synaptonemal complexdevelops, and is not completed until near the end of prophase I. Crossover usually occurs when matching regions on matching chromosomes break and then reconnect to the other chromosome.