A female fly that has miniature wings and sepia eyes is crossed with a male that has normal wings and is homozygous for red eyes. The F1 are intercrossed to produce the F2. Give the phenotypes and their proportions expected in the F1 and F2 flies from this cross.

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.