Explain the chromosomal basis for sex determination in Drosophila and humans. Use correct symbols to explain the different results of reciprocal monohybrid crosses involving a sex-linked trait. Predict the results of crosses involving alleles of genes carried on the X chromosome. Describe the relationship between chromosomes and genes. Explain the behavior of alleles of genes carried on the same chromosome. Explain how the proportion of gamete types made by an F1 dihybrid reflects the physical distance between the genes. Correlate % recombinant gametes with linkage or with independent assortment..