Alternative explanation: linkage, recombination and map distance
The value of sex
Diploid species have one set of chromosomes from the mother (let us call them m1 – m10 for a species with 10 chromosome pairs) and one from the father (f1 – f10): m1f1, m2f2, m3f3 …m10f10. Let's assume these parents have been crossed and we are considering the F1 of this cross. Sexual propagation (i.e. involving meiosis) is very important, because it favors efficient recombination of genes through two systems:
1. Cross-over between homologues in the F1 meiosis
This can occur between the chromatids of homologous chromosomes, so in this F1 between m1 and f1, and m2 and f2 etc. (m1 is one homologue of chromosome 1, f1 the other in the F1 of this cross)
This results in 'mixed' chromosomes, which contain pieces of m1 and pieces of f1, m2/f2 etc. Let us indicate them with m1' and f1' etc., depending on the chromosome (m1 or f1) from which they got their centromere.
2. Independent assortment of chromosomes in the F1 meiosis
After the first meiotic division, each cell contains one random copy of each chromosome, e.g. m1', m2', f3', m4', f5', f6', m7', f8', f9', m10', or any other combination.
The value of this recombination is that in the progeny the genetic information between chromosomes and within chromosomes is mixed to form novel combinations of genes. Most likely, there will be some progeny members with a combination of genes that is superior to the parent plants.