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Biology LibreTexts

Genetic Crosses That Involve 2 Traits

  • Page ID
    21236
  • In rabbits, black hair is dominant to brown hair. Also in rabbits, long straight ears are dominant to floppy ears.

    bunny.png

    These letters represent the genotypes and phenotypes of the rabbits:

    BB = black hair

    Bb = black hair

    bb = brown

    EE = long ears

    Ee = long ears

    ee = floppy ears

    1. A male rabbit with the genotype BBee is crossed with a female rabbit with the genotype bbEe The square is set up below. Fill it out and determine the phenotypes and proportions in the offspring.

    cross.png

    How many out of 16 have black hair and long ears?

    How many out of 16 have black hair and floppy ears?

    How many out of 16 have brown hair and long ears?

    How many out of 16 have brown hair and floppy ears?


    2. Show the cross: GgBb x ggBb

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    How many out of 16 have black hair and long ears?

    How many out of 16 have black hair and floppy ears?

    How many out of 16 have brown hair and long ears?

    How many out of 16 have brown hair and floppy ears?

    fly.png

    3. Fruit flies are organisms commonly used in genetic studies. They reproduce quickly and have several traits that can be measured. One trait is the vestigial wing trait, which is recessive. Most flies have red eyes, but the sepia eye trait is recessive. The image shows a mutant double recessive fly (ggee).

    A fly that is heterozygous for both traits (GgEe) is crossed with one that has vestigial wings and sepia eyes (ggee). Set up a Punnett square and list the phenotypic ratio of the offspring.

    blank.png

    How many are normal wings, red eyes?

    How many are normal wings, sepia eyes?

    How many are vestigial wings, red eyes?

    How many are vestigial wings, sepia eyes?

    fly 2.png

    4. Show a dihybrid cross for fruit flies. GgEe x GgEe. Be careful when counting the number for each phenotype, it is easy to make a mistake. Write the phenotype ratios below.

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