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9 February, 16:04

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.

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  1. 9 February, 18:30
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    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.
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