A diploid-triploid human mosaic with cytogenetic evidence of double fertilization.

The karyotype 46,XX/69,XXY was found in a 13-year-old mentally subnormal patient with club feet, strabismus, eunuchoid habitus, small penis, midscrotal urethrovaginal opening, small descended left testis, and small undescended right testis; no ovarian tissue could be found at laparotomy. Triploid:diploid cell ratios were 60:40 and 4:96 in skin fibroblasts and curculating lymphocytes, respectively. In the triploid line, two of the no. 13 chromosomes had unusually large satellites and one of the no. 22 chromosomes had a brightly fluorescent zone on its short arms. The patient's father was heterozygous for both these autosomal markers; the mother carried neither marker. This, together with the single Y, indicated that the extra haploid set was derived from the father. Of several possible mechanisms, we favor the suggestion that double fertilization occurred; one sperm nucleus immediately fused with the egg nucleus producing the diploid line; the second sperm nucleus was incorporated later into one of the two cells resulting from the first division of the zygote, producing the triploid line.