Dihybrid Crosses and Non-mendelian genetics

Leaves from two white clover plants, each with a different pattern, are shown.

The leaf patterns are genetically determined by alleles of a single gene. Plant 1 is homozygous for the chevron allele. Plant 2 is homozygous for the oval allele. The chevron and oval alleles are codominant.

If plant 1 and plant 2 are crossed, the codominance of the alleles will most likely result in which of the following leaf patterns on the offspring plants?

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In humans, B is the allele for brown eyes and b is the allele for blue eyes. Two brothers both have brown eyes, but one of them has both the B and b  alleles while the other only has B  alleles. Which statement is true about the brothers?

• They have the same genotype and phenotype.

• They have different phenotypes and genotypes.

• They have the same phenotype but different genotypes.

• They have the same genotype but different phenotypes.

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The below shows the genotypes that result in four different blood types in humans.

Based on the information in the table, which of the following describes alleles I ^A and I ^B ?

• The I ^A and I ^B alleles show sex linkage.

• The I ^A allele is recessive to the I ^B allele.

• The I ^A allele is dominant to the I ^B allele.

• The I ^A and I ^B alleles show codominance.

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In snapdragons, the allele for red flower color (C^R ) is incompletely dominant to the allele for white flower color (C^W ). Snapdragons that are heterozygous for flower color have a pink phenotype.

Which of the following crosses could yield all three flower color phenotypes (red, white, and pink) among the offspring?

• C^RC^R × C^WC^W

• C^RC^R × C^RC^W

• C^RC^W × C^RC^W

• C^RC^W × C^WC^W

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Which of the following characteristics is a lion least likely to pass on to its offspring?

• colors of its fur

• length of its tail

• scars on its leg

• size of its body

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In Holstein cattle the allele for black hair color (B) is dominant over the allele for red hair

color (b), and the allele for polled (P), or lacking horns, is dominant over the allele for having

horns (p).

What is the expected phenotypic ratio of the offspring of a BbPp × BbPp cross if these alleles

sort independently?

• 16 black/polled : 0 black/horned : 0 red/polled : 0 red/horned

• 12 black/polled : 0 black/horned : 0 red/polled : 4 red/horned

• 4 black/polled : 4 black/horned : 4 red/polled : 4 red/horned

• 9 black/polled : 3 black/horned : 3 red/polled : 1 red/horned

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In a plant called jimsonweed, flowers can be white or purple. A jimsonweed plant with white flowers is crossed with a jimsonweed plant with purple flowers. All of the offspring have purple flowers.

Based on the results of the cross, which of the following statements most likely describes the alleles for flower color in jimsonweed?

• The allele for purple flowers is recessive to the allele for white flowers.

• The allele for purple flowers is dominant to the allele for white flowers.

• The allele for purple flowers has mutated more times than the allele for white flowers.

• The allele for purple flowers is on a different chromosome than the allele for white flowers.

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In summer squash, white fruit color (W) is dominant over yellow fruit color (w) and disk-shaped fruit (D) is dominant over sphere-shaped fruit (d). If a squash plant homozygous for white and disk-shaped fruit is crossed with a yellow, sphere-shaped fruit plant, what will the phenotypic ratio of their offspring?

• 1:0:0:0

• 0:1:0:0

• 0:0:1:0

• 0:0:0:1

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In horses, black is dependent upon a dominant gene, B, and chestnut upon its recessive allele, b. The trotting gait is due to a dominant gene, T, the pacing gait to its recessive allele, t. If a homozygous black pacer is mated to a homozygous chestnut trotter, what will be the appearance of the F1 generation?

• 0 % black and trotters

• 25% black and trotters

• 50% black and trotters

• 100% black and trotters

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Facial dimples and free earlobes are both considered dominant human traits. What are the

expected phenotypes of the offspring of a female with dimples and free earlobes (DDFf) and a

male with no dimples and attached earlobes (ddff)?

• 50% with dimples and free earlobes and 50% with dimples and attached earlobes

• 50% with dimples and free earlobes and 50% with no dimples and attached earlobes

• 75% with dimples and free earlobes and 25% with no dimples and attached earlobes

• 75% with dimples and attached earlobes and 25% with no dimples and free earlobes

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