It has been proposed in the stem of (1) that "Gynura bicolor (2N=24) is dioecious", and its sex determination mode is XY type. Therefore, it is necessary to study 13 chromosomes (1 1 autosome +X chromosome +Y chromosome) to determine the genome of Solanum nigrum.

(2) The disease resistance of female Loucai is controlled by dominant gene B. If these alleles exist in homologous segments of X and Y chromosomes, their gene composition is similar to that of autosomes, that is, there are three genotypes XBYb, XbYB and XBYB in disease-resistant male individuals.

(3) Because recessive female individuals and dominant male individuals hybridize with X chromosome in recessive inheritance, the phenotype of their offspring is related to sex, so it is inferred by hybridization experiment whether the disease-resistant gene is located in homologous fragments of X and Y chromosomes or only on X chromosome, and the phenotypes of female parent and male parent should be non-disease-resistant (female) and disease-resistant (male) respectively. Predict the experimental results and infer the corresponding conclusions: ① both female and male offspring are disease-resistant, then ② female offspring are disease-resistant and male offspring are not disease-resistant, so this gene is only located on the X chromosome.

So the answer is:

( 1) 13?

(2)XBYB、XBYB、XBYB；

(3) Not resistant to disease (female) and not resistant to disease (male)?

(1) If both female and male offspring show disease resistance, the gene is located in homologous segments of X and Y chromosomes.

② The female offspring all showed disease resistance, while the male offspring did not, so this gene was only located on the X chromosome.