Examples of Punnett Square Analysis: Single Trait Crosses

🧬 Quick Study Guide

• 🌱 Basic Concept: A Punnett square is a diagram used to predict the genotypes and phenotypes of offspring from a genetic cross.
• 📝 Single Trait Cross: Focuses on the inheritance of one specific trait (e.g., flower color, plant height).
• 🔑 Key Terms:
  • 🧬 Gene: A unit of heredity.
  • 🍎 Allele: A variant form of a gene (e.g., A or a).
  • 💪 Dominant Allele: Masks the expression of the recessive allele (represented by a capital letter, e.g., A).
  • 🧘 Recessive Allele: Only expressed when two copies are present (represented by a lowercase letter, e.g., a).
  • 💯 Genotype: The genetic makeup (e.g., AA, Aa, aa).
  • 👁️ Phenotype: The observable characteristics (e.g., purple flowers, white flowers).
  • ✨ Homozygous: Having two identical alleles for a trait (e.g., AA or aa).
  • 🎭 Heterozygous: Having two different alleles for a trait (e.g., Aa).
• 🧮 Punnett Square Setup:
  • ✏️ Write the possible alleles of one parent across the top.
  • ✍️ Write the possible alleles of the other parent down the side.
  • 🧩 Fill in each box with the combination of alleles from the corresponding row and column.
• ➗ Calculating Probabilities:
  • Use the Punnett square to determine the probability of each genotype and phenotype.
• 🧪 Example Cross: Crossing two heterozygous individuals (Aa x Aa) yields the following genotypic ratio: 1 AA : 2 Aa : 1 aa. The phenotypic ratio depends on whether the trait is dominant or recessive.

🧪 Practice Quiz

1. What is the phenotype of an organism?

   1. Its genetic makeup.
   2. Its physical characteristics.
   3. The possible alleles for a trait.
   4. The process of meiosis.

2. In a monohybrid cross between two heterozygous parents (Aa), what is the probability of producing a homozygous recessive offspring (aa)?

   1. 25%
   2. 50%
   3. 75%
   4. 100%

3. What does a Punnett square predict?

   1. The exact number of offspring.
   2. The possible genotypes and phenotypes of offspring.
   3. The mutation rate of a gene.
   4. The age of the parents.

4. Which of the following genotypes is heterozygous?

   1. AA
   2. aa
   3. Aa
   4. None of the above.

5. If tall (T) is dominant to short (t), what is the genotype of a short plant?

   1. TT
   2. Tt
   3. tT
   4. tt

6. In a cross between a homozygous dominant (AA) and a homozygous recessive (aa) individual, what will be the genotype of all the offspring?

   1. AA
   2. aa
   3. Aa
   4. None of the above.

7. What term refers to the different versions of a gene?

   1. Genotype
   2. Phenotype
   3. Allele
   4. Chromosome