Respuesta :
Answer: pairing of homologous chromosomes
Explanation: There are two types of reproduction- asexual and sexual. But it is during sexual reproduction only that variation among offsprings is generated. When the sister chromosomes from paternal and maternal cells come together and pair up, then only variation is generated. This is how a kitten with both white and black color fur is generated. Pairing of homologous chromosomes leads to crossing over and variation takes place.