Mendel's Laws of Genetics

Use the information to answer the following question. A student crossed plants that were heterozygous for the traits of flower color, seed color, and seed shape as part of an investigation designed to verify the results of Gregor Mendel’s experiments. The table displays the results.

• White flowers are dominant.

• Yellow seeds are recessive.

• Wrinkled seeds are recessive.

• Purple and white flowers are codominant.

Answer explanation

Wrinkled seeds are recessive, as demonstrated in Mendel's experiments. The presence of wrinkled seeds in the offspring indicates that the trait is not expressed when a dominant allele is present.

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In a certain species of flower, red color (R) is dominant over white color (r). If two heterozygous flowers (Rr) are crossed, what is the probability of obtaining a white flower in the offspring?

• 75%

• 0%

• 25%

• 50%

Answer explanation

When crossing two heterozygous flowers (Rr), the possible genotypes are RR, Rr, Rr, and rr. Only the rr genotype results in a white flower. Thus, the probability of obtaining a white flower is 1 out of 4, or 25%.

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In a population of rabbits, the allele for long ears (L) is dominant over the allele for short ears (l). If a homozygous long-eared rabbit is crossed with a short-eared rabbit, what will be the phenotype of the offspring?

• All long-eared

• All short-eared

• 50% long-eared, 50% short-eared

• 75% long-eared, 25% short-eared

Answer explanation

The homozygous long-eared rabbit has the genotype LL. When crossed with a short-eared rabbit (ll), all offspring will inherit one L allele from the long-eared parent, resulting in the genotype Ll, which expresses the long-eared phenotype.

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In a certain species of plant, tall height (T) is dominant over short height (t). If a homozygous tall plant is crossed with a heterozygous plant, what is the probability of obtaining a short plant in the offspring?

• 75%

• 50%

• 25%

• 0%

Answer explanation

In this cross, the homozygous tall plant (TT) and the heterozygous plant (Tt) can produce offspring with genotypes TT and Tt. All offspring will be tall, so the probability of obtaining a short plant (tt) is 0%.

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In a population of birds, the allele for blue feathers (B) is dominant over the allele for white feathers (b). If two heterozygous birds are crossed, what is the expected phenotypic ratio of the offspring?

• 2:1

• 1:1

• 3:1

• 1:2:1

Answer explanation

When two heterozygous birds (Bb) are crossed, the possible genotypes are BB, Bb, Bb, and bb. This results in three blue-feathered (BB and Bb) and one white-feathered (bb) offspring, giving a phenotypic ratio of 3:1.

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A farmer is trying to increase the diversity of corn kernel color in his crops. If the trait for corn color is controlled by two alleles and yellow corn (B) is completely dominant over white corn (b), which combination of corn should he cross to get the highest variety of genotypes in the next generation?

• BB x BB

• Bb x bb

• Bb x Bb

• BB x bb

Answer explanation

Crossing Bb x Bb produces the highest variety of genotypes: BB, Bb, and bb. This results in a mix of yellow and white kernels, maximizing diversity compared to other combinations.

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A rooster with grey feathers is crossed with a hen of the same phenotype. They produce 15 chicks with grey feathers, 7 chicks with black feathers, and 8 chicks with white feathers. What is the simplest explanation for this inheritance pattern?

• The inheritance pattern is incomplete dominance, which produces grey offspring when black and white parents are crossed.

• The inheritance pattern is codominance, which produces grey offspring when black and white parents are crossed.

• The inheritance pattern is incomplete dominance, which produces black and white offspring when both dominant alleles are present.

• The inheritance pattern is codominance, which produces black and white offspring when both dominant alleles are present.

Answer explanation

The inheritance pattern is incomplete dominance because crossing black and white parents produces grey offspring, as seen in the 15 grey chicks. This indicates that neither color is completely dominant over the other.

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In a genetic experiment, a plant with genotype AaBb is crossed with another plant with genotype AaBb. Assuming independent assortment, what is the probability of obtaining an offspring with genotype AABB?

• 1/16

• 1/8

• 1/4

• 1/2

Answer explanation

To find the probability of AABB, calculate the probability of A from Aa (1/2) and B from Bb (1/2). Thus, P(AABB) = (1/2 * 1/2) * (1/2 * 1/2) = 1/16. Therefore, the correct answer is 1/16.

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In a genetic study, a plant with genotype AaBbCc is crossed with another plant with genotype AaBbCc. Assuming independent assortment, what is the probability of obtaining an offspring with genotype AABbcc?

• 1/64

• 1/32

• 1/16

• 1/8

Answer explanation

To get AABbcc, we need AA (1/4), Bb (1/2), and cc (1/4). The probability is (1/4) * (1/2) * (1/4) = 1/32. Thus, the correct answer is 1/32.

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The gene for round peas (R) in a pea plant is dominant over the gene for wrinkled peas (r). In a cross between one heterozygous parent and one homozygous wrinkled pea parent, we can predict that what percentage of the offspring will have round peas?

• 100%

• 50%

• 75%

• 25%

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