Recombinant chromosomes have a mix of paternal and maternal alleles due to:

a. Random fertilization

b. Linkage

c. Independent assortment

d. Crossing over

e. Mutation

d. Crossing over

Explanation:

Crossing over is a process that occurs during the meiosis (prophase 1) and represents the exchange of genetic material between non-sister chromatids of homologous chromosomes. As a result of this process new recombinant chromosomes (new allelic combinations in the daughter cells) are formed. Crossing over is a source of genetic variation.