Answer and Explanation:
- The gene that expresses the size of the wing is X-linked. The dominant allele expresses long wings, XM, while the recessive allele expresses miniature wings, Xm.
- The gene that expresses the color of the eyes is autosomal. The dominant allele expresses red color, S, and the recessive allele expresses sepia color, s.
A female fly that has miniature wings and sepia eyes (XmXm ss) is crossed with a male that has normal wings and is homozygous for red eyes (XMY SS).
The F1 are intercrossed to produce the F2.
1º Cross:
Parental) XmXm ss x XMY SS
Gametes) Xms Xms Xms Xms
XMS XMS YS YS
Punnet Square) Xms Xms Xms Xms
XMS XMXmSs XMXmSs XMXmSs XMXmSs
XMS XMXmSs XMXmSs XMXmSs XMXmSs
YS XmY Ss XmY Ss XmY Ss XmY Ss
YS XmY Ss XmY Ss XmY Ss XmY Ss
F1) 1/2 or 50% of the progeny are females and the other 1/2 or 50% are males
100% of the females (1/2 or 50% of the progeny) are long-winged and red-eyed
100% of the males (1/2 or 50% of the progeny) are miniature.winged and red-eyed.
2º Cross:
Parental) XMXm Ss x XmY Ss
Gametes) XMS XMs XmS Xms
XmS Xms YS Ys
Punnet Square) XMS XMs XmS Xms
XmS XMXm SS XMXm Ss XmXm SS XmXm Ss
Xms XMXm Ss XMXm ss XmXm Ss XmXm ss
YS XMY SS XMY Ss XmY SS XmY Ss
Ys XMY Ss XMY ss XmY Ss XmY ss
F2) 8/16=4/8=1/2 or 50% of the progeny are females and the other 1/2 or 50% are males
Females (8/16):
- 3/8 of the females are long-winged and red-eyed, XMX- S-
- 1/8 of the females are long-winged and sepia-eyed, XMX- ss
- 3/8 of the females are miniature-winged and red-eyed, XmXm S-
- 1/8 of the females are miniature-winged and sepia-eyed, XmXm ss
Males (8/16):
- 3/8 of the males are long-winged and red-eyed, XMY S-
- 1/8 of the males are long-winged and sepia-eyed, XMY ss
- 3/8 of the males are miniature-winged and red-eyed, XmY S-
- 1/8 of the males are miniature-winged and sepia-eyed, XmY ss
Note: The symbol "-" means that in its place might be a recessive allele or a dominant allele. For example, S- means that it might be SS or Ss.
