Punnett Square quiz for Grade 8 science with answers

🧬 Quick Study Guide

• 🌱 Genes and Alleles: Genes are segments of DNA that determine traits. Alleles are different versions of a gene (e.g., 'T' for tall, 't' for short).
• ➕ Dominant and Recessive Alleles: Dominant alleles (uppercase, e.g., 'T') mask recessive alleles (lowercase, e.g., 't'). You need two recessive alleles to express the recessive trait (tt).
• 🧮 Genotype and Phenotype: Genotype is the genetic makeup (e.g., TT, Tt, tt). Phenotype is the physical expression of the trait (e.g., tall or short).
• ➗ Homozygous and Heterozygous: Homozygous means having two identical alleles (TT or tt). Heterozygous means having two different alleles (Tt).
• ⚗️ Punnett Square Basics: A Punnett Square is a diagram used to predict the probability of offspring genotypes and phenotypes.
• ✍️ Monohybrid Cross: A cross involving only one trait (e.g., height).
• 📊 Example: If you cross a heterozygous tall plant (Tt) with another heterozygous tall plant (Tt), the possible genotypes of the offspring are TT, Tt, and tt. The possible phenotypes are tall and short.

🧪 Practice Quiz

1. What does a Punnett Square predict?
   1. A) The exact traits of the offspring.
   2. B) The probability of different genotypes and phenotypes in offspring.
   3. C) The age of the offspring.
   4. D) The size of the offspring.
2. In a Punnett Square, what do the letters inside the boxes represent?
   1. A) The parents' genotypes.
   2. B) The possible genotypes of the offspring.
   3. C) The dominant alleles only.
   4. D) The recessive alleles only.
3. What is the phenotype of an organism with the genotype 'tt' if 'T' is the allele for tallness and 't' is the allele for shortness, and 'T' is dominant?
   1. A) Tall.
   2. B) Short.
   3. C) Medium height.
   4. D) Cannot be determined.
4. What does it mean for an organism to be heterozygous for a trait?
   1. A) It has two identical alleles for that trait.
   2. B) It has two different alleles for that trait.
   3. C) It only has dominant alleles.
   4. D) It only has recessive alleles.
5. If a plant with genotype 'Tt' is crossed with a plant with genotype 'tt', what percentage of the offspring would you expect to have the genotype 'tt'?
   1. A) 0%.
   2. B) 25%.
   3. C) 50%.
   4. D) 75%.
6. In a monohybrid cross between two heterozygous parents (Aa), what is the probability of producing a homozygous recessive offspring (aa)?
   1. A) 25%.
   2. B) 50%.
   3. C) 75%.
   4. D) 100%.
7. Which of the following genotypes is homozygous dominant?
   1. A) Tt.
   2. B) tt.
   3. C) TT.
   4. D) None of the above.