Science, Grade 6


Table Of Contents: Crossing-Over

1. Homologous Chromosomes
Homologous chromosomes move together during synapsis in prophase of meiosis I. Proteins hold these chromosome pairs very close together.
2. Crossing-Over
Sometimes homologous chromosomes exchange segments of DNA. This is called crossing-over. When crossing-over occurs, each chromatid ends up with a unique sequence of DNA.
3. Crossed-Over Genes
At the completion of meiosis, the new combinations of crossed-over genes are found in the sex cells.
4. Offspring Variation
Crossing-over adds variation to the offspring and ultimately contributes to the evolution of a species.