Steps for performing a test cross

📚 Quick Study Guide

• 🌱 A test cross is used to determine the genotype of an individual showing a dominant trait.
• 🤔 The unknown individual is crossed with a homozygous recessive individual.
• 🧬 If any offspring show the recessive phenotype, the unknown individual is heterozygous.
• 📊 If all offspring show the dominant phenotype, the unknown individual is homozygous dominant.
• 📝 The phenotypic ratios of the offspring reveal the genotype of the parent with the dominant trait.
• 🧪 Key genotypes to remember: Homozygous Dominant (e.g., $AA$), Heterozygous (e.g., $Aa$), Homozygous Recessive (e.g., $aa$).

Practice Quiz

1. What is the primary purpose of performing a test cross?
   1. To determine the phenotype of an unknown individual.
   2. To determine the genotype of an unknown individual.
   3. To create new genetic variations.
   4. To predict the sex of offspring.
2. With what genotype should an unknown dominant phenotype be crossed in a test cross?
   1. Homozygous dominant.
   2. Heterozygous.
   3. Homozygous recessive.
   4. Any genotype.
3. In a test cross, if all offspring display the dominant trait, what is the likely genotype of the unknown parent?
   1. Homozygous recessive.
   2. Heterozygous.
   3. Homozygous dominant.
   4. Unable to determine without more information.
4. In a test cross, if some offspring display the recessive trait, what is the genotype of the unknown parent?
   1. Homozygous dominant.
   2. Homozygous recessive.
   3. Heterozygous.
   4. Cannot be determined.
5. What phenotypic ratio in the offspring of a test cross would indicate the unknown parent is heterozygous?
   1. 3:1 (Dominant:Recessive).
   2. 1:1 (Dominant:Recessive).
   3. All dominant.
   4. All recessive.
6. If you cross an unknown plant showing purple flowers with a white-flowered plant (homozygous recessive), and half the offspring have purple flowers and half have white flowers, what is the genotype of the unknown parent?
   1. PP.
   2. Pp.
   3. pp.
   4. Cannot be determined.
7. In a certain species, black fur (B) is dominant over brown fur (b). You have an individual with black fur. You perform a test cross and find that approximately 50% of the offspring have brown fur. What is the genotype of the black-furred parent?
   1. BB
   2. Bb
   3. bb
   4. It's impossible to determine