Explanation: The allele for detached earlobes E is dominant over the allele for attached earlobes e. Because E is a dominant gene, a boy who has detached earlobes must have at least one E allele. He can either have a genotype EE or Ee, the two genotypes will manifest outwardly as detached earlobes. Because E is dominant and is capable of expressing itself in the presence of a recessive gene e, the genotype Ee will also manifest outwardly as detached earlobes.
Crossing over is a biological occurrence that happens during meiosis when the paired homologs, or chromosomes of the same type, are lined up. Hope this helps :)
