Pedigree Analysis Builder
Build and analyze pedigrees to trace inheritance patterns of genetic traits through family trees. Learn to identify autosomal dominant, autosomal recessive, X-linked recessive, and X-linked dominant inheritance patterns by examining affected individuals across generations. Practice determining genotypes, calculating probabilities, and distinguishing between different modes of inheritance using standard pedigree symbols.
MAPPING THE FAMILY TREE
A **pedigree** is a visual representation of a family's genetic history over several generations. It allows biologists and genetic counselors to track the inheritance patterns of specific traits or disorders, such as whether a trait is dominant, recessive, autosomal, or sex-linked.
SYMBOLS AND PATTERNS
In a pedigree, circles represent females and squares represent males. Shaded shapes indicate individuals who express the trait. Horizontal lines between a circle and square represent a mating, while vertical lines lead to offspring. By analyzing which individuals are affected, you can deduce the genotypes of parents and predict the probability of traits appearing in future generations.
HOW TO USE THIS VISUALIZATION
1. **Select a Trait**: Choose between Autosomal Dominant, Autosomal Recessive, or X-linked Recessive modes. 2. **Generate Pedigree**: Click to create a random family tree based on the selected inheritance pattern. 3. **Assign Genotypes**: Click on individuals to test your hypothesis about their genotype. **Try This**: Select "Autosomal Recessive." Find a pair of unaffected parents who have an affected child. What MUST the genotypes of those parents be? How does this prove the trait is recessive?
AP EXAM CONNECTION
Unit: Unit 5: Heredity (Topic 5.4)
Learning Objective: IST-1.J
COMMON MISCONCEPTIONS
- Assuming all rare traits are recessive.
- Confusing "autosomal" with "sex-linked" patterns.
- Thinking dominant traits are always more common in a population.
KEY TAKEAWAYS
- Squares = Male, Circles = Female.
- Shaded = Affected/Trait expressed.
- Vertical patterns often suggest dominance.
- Skipping generations suggests recessiveness.
PRACTICE QUESTIONS
Q1 (CONCEPTUAL): If two unaffected parents have a daughter with an autosomal recessive disorder, what are the parents' genotypes?
Show Answer & Explanation
Answer: Both parents must be heterozygous (carriers).
Explanation: For a child to express a recessive trait, they must inherit one recessive allele from each parent. If the parents do not express the trait, they must carry the dominant allele as well.
Q2 (CONCEPTUAL): In a pedigree for an X-linked recessive trait, can an unaffected father have an affected daughter?
Show Answer & Explanation
Answer: No.
Explanation: A daughter inherits one X chromosome from her father. If the father is unaffected, his single X chromosome must carry the dominant (normal) allele, which would prevent the daughter from expressing the recessive trait.
