Dihybrid Crosses and Pedigrees Worksheet
Name: _______________________________
Date: _______________________________
Instructions
Complete the worksheet by answering the questions below. Make sure to show your work where applicable. This
worksheet will help you understand the significance of chromosome reduction, independent assortment, and
crossing-over during meiosis, and predict genetic outcomes using dihybrid crosses and pedigrees.
Part 1: Understanding Meiosis and Genetic Diversity
1. Short Answer: Explain how chromosome reduction during meiosis contributes to genetic diversity in
sexually reproducing organisms.
Answer:
2. Multiple Choice: Which of the following processes during meiosis helps increase genetic variation?
a) DNA replication b) Chromosome reduction c) Independent assortment d) Mitosis
Answer: ________
3. Short Answer: Describe the role of crossing-over in meiosis and how it contributes to genetic diversity.
Answer:
Part 2: Predicting Genetic Outcomes with Dihybrid Crosses
4. Dihybrid Cross: In peas, the allele for yellow seeds (Y) is dominant over green seeds (y), and the allele for
round seeds (R) is dominant over wrinkled seeds (r). Perform a dihybrid cross between two heterozygous pea
plants (YyRr x YyRr). Use a Punnett square to predict the phenotypic ratio of the offspring.
Punnett Square:
YR Yr yR yr
YR
Yr
yR
yr
Phenotypic Ratio:
5. Short Answer: Explain the difference between incomplete dominance and codominance. Provide an
example for each.
Answer:
Part 3: Analyzing Pedigrees
6. Pedigree Analysis: Below is a simple pedigree chart. Use it to answer the following questions.
a) Identify the pattern of inheritance (e.g., autosomal dominant, autosomal recessive, sex-linked).
Answer: ___________________________
b) Predict the genotype of individual III-2 if individual I-1 is homozygous recessive.
Answer: ___________________________
Part 4: Challenge Question
7. Challenge: Consider a scenario where a trait is determined by multiple alleles and shows codominance.
Explain how this can affect the variety of phenotypes in a population.
Answer:
Teacher's Note: This worksheet covers key concepts of genetic diversity and inheritance patterns necessary for
understanding ninth-grade biology curriculum standards. Encourage students to discuss their answers and
collaborate on the dihybrid crosses for deeper understanding.