Generating Gynandromorphs Using Horka Mutation

The antimorphic lds[Hor-D] mutation causes dominant loss of paternally inherited chromosomes in early embryonic mitoses. Experimentally, the "Horka" mutation is useful for inducing X chromosome loss to generate gynandromorphs.

This method was described in Szabad et al. (1995).

Janos Szabad's tips for maximizing the recovery of gynandromorphs

Gyndandromorphs are more common when mwh[1] lds[Hor-D] e[1]/TM3, Sb[1] Ser[1] males from stock 42293 are crossed to y[1] v[1] f[1] mal[F1] virgin females from stock 180 than in crosses to females of other genotypes. Gynandromorphs comprise ~20% of the progeny of y[1] v[1] f[1] mal[F1] females and 1-2% of progeny of other females. The genetic basis of this strain difference is not known. Gynandromorphs eclose with a 2-3 day delay. For best results, cultures should not be overcrowded.

There are two predominate classes of male progeny: y[1] v[1] f[1] mal[F1]/Y male progeny from regular Y-bearing sperm and y[1] v[1] f[1] mal[F1]/0 male progeny from nullo-Y sperm produced by the high rate of nondisjunction in lds[Hor-D] males. Both have creamy orange eyes from the combination of v and mal mutations. Other progeny appear to be males with red eye color, but they are actually crypto-gynandromorphs. Although their eyes are v[-] in genotype, the presence of heterozygous v[+]/v[-] diplo-X tissue in their bodies leads to red eyes from vermilion nonautonomy.

Some progeny of lds[Hor-D] males have both normal bristles and short, thin bristles as shown below. They are diplo-4//haplo-4 mosaics resulting from loss of the paternal fourth chromosome. The short, thin bristles result from loss of one copy of the haploinsufficient Minute gene RpS3A.

Haplo-4 mosaic

To generate gynandromorphs with one red and one white eye and with half y[-] pigmentation as shown below, mate homozygous y[-] w[-] females to lds[Hor-D]/TM3, Sb[1] Ser[1] males. Other interesting markers for distinguishing female from male tissue include sn[-] and f[-] mutations and X-linked transgenes expressing marker proteins.


It is often desirable to examine the external phenotypes of gynandromorphs (and other flies) in flattened cuticle preparations. A convenient method is described in Szabad (1978).

A note on making gynandromorphs using a ring-X chromosome

Historically, gynandromorphs have been generated most often using a ring-X chromosome called R(1)2, In(1)w[vC]. Ring-X stocks must be selected continually for mitotic instability to be experimentally useful in recovering gynandromorphs. R(1)2, In(1)w[vC] stocks in the Bloomington collection have not been maintained under selection and they have stabilized. It is not clear if they could be destabilized by selection.