Real-world examples of dominant and recessive alleles.

📚 Quick Study Guide

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• Alleles: Different versions of a gene. Every individual has two alleles for each gene, one inherited from each parent.
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• Dominant Allele: The allele that expresses its trait even when paired with a recessive allele. Represented by a capital letter (e.g., A).
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• Recessive Allele: The allele that expresses its trait only when paired with another recessive allele. Represented by a lowercase letter (e.g., a).
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• Genotype: The genetic makeup of an individual (e.g., AA, Aa, aa).
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• Phenotype: The observable traits of an individual (e.g., brown eyes, blue eyes).
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• Homozygous: Having two identical alleles for a gene (e.g., AA or aa).
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• Heterozygous: Having two different alleles for a gene (e.g., Aa).

🧪 Practice Quiz

1. Which of the following is an example of a dominant trait in humans?
1. Attached earlobes
2. Blue eyes
3. Widow's peak
4. Red hair
2. In pea plants, the allele for tall plants (T) is dominant to the allele for short plants (t). What is the phenotype of a pea plant with the genotype Tt?
1. Short
2. Medium
3. Tall
4. Dwarf
3. Cystic fibrosis is a recessive genetic disorder. What is the genotype of an individual who is a carrier of cystic fibrosis but does not have the disease? (Let C = normal allele, c = cystic fibrosis allele)
1. CC
2. cc
3. Cc
4. None of the above
4. In guinea pigs, black fur (B) is dominant to white fur (b). If a heterozygous black guinea pig (Bb) is crossed with a homozygous white guinea pig (bb), what percentage of their offspring is expected to have white fur?
1. 0%
2. 25%
3. 50%
4. 75%
5. Which of the following statements is true regarding recessive alleles?
1. They are always expressed in the phenotype.
2. They are only expressed in the phenotype when homozygous.
3. They are more common than dominant alleles.
4. They are not inheritable.
6. In humans, the ability to roll the tongue is dominant (R) over the inability to roll the tongue (r). If both parents are heterozygous for this trait (Rr), what is the probability that their child will be able to roll their tongue?
1. 25%
2. 50%
3. 75%
4. 100%
7. What is the term for a gene that has multiple alleles present in a population?
1. Polygenic
2. Codominant
3. Multiple alleles
4. Incomplete dominance