A free printable pedigree analysis worksheet for Grade 11 biology.
Students learn pedigree symbols, analyse three drawn family pedigrees (albinism, Huntington’s disease and haemophilia), identify autosomal recessive, autosomal dominant and X-linked recessive patterns with evidence, write genotypes, calculate carrier probabilities and draw their own pedigree. Includes 23 questions (24 marks) and a full answer key.
This free pedigree worksheet teaches students to read family trees the way genetic counsellors do. After learning the symbols, they analyse three drawn pedigrees: albinism (autosomal recessive), Huntington's disease (autosomal dominant) and haemophilia (X-linked recessive).
For each family, students decide the inheritance pattern, justify it with evidence, rule out other patterns, write genotypes and calculate carrier probabilities. They finish by drawing a pedigree from a written description. Each pedigree has been checked by computer against every inheritance pattern, so the answers hold up.
It supports the Ontario Grade 11 biology curriculum expectations in the Genetic Processes unit.
How to Read a Pedigree
A pedigree is a family tree that tracks one trait. Squares are males, circles are females, and shaded symbols are affected. A horizontal line joins a couple, and a vertical line leads down to their children. Generations are labelled with Roman numerals and individuals are numbered left to right, so "II-3" means the third person in generation II.
Every question on the pedigree worksheet comes back to two tests: unaffected parents with an affected child means recessive; affected parents with an unaffected child means dominant. For background, see pedigree charts on Wikipedia.
Autosomal Recessive Pedigrees
In Pedigree 1, unaffected parents I-1 and I-2 have an affected son, so albinism is recessive and both parents are carriers (Aa). Their unaffected daughter II-1 has a 2/3 chance of being a carrier, because only the AA, Aa and Aa outcomes are possible for an unaffected child. The affected daughter III-2 has an unaffected father, which rules out X-linked inheritance.
Autosomal Dominant Pedigrees
In Pedigree 2, affected parents II-4 and II-5 have an unaffected daughter, which proves Huntington's disease is dominant. Both parents must be Aa, so each of their children has a 3/4 chance of being affected. The affected son II-4 has an unaffected mother, so the trait can't be X-linked dominant.
X-Linked Recessive Pedigrees
In Pedigree 3, only males have haemophilia, and each affected son has unaffected parents, the classic X-linked recessive pattern. Women I-2 and II-3 must be carriers (XHXh), so each son of II-3 has a 1/2 chance of haemophilia. To practise sex-linked Punnett squares, use the codominance and incomplete dominance worksheet.
Pedigree Worksheet Practice Questions
These questions match the pedigree worksheet PDF, which has larger pedigrees and ruled answer space.
Part A – Pedigree Symbols
Questions 1–6: name six symbols (affected and unaffected males and females, a couple line and a carrier).
Part B – Pedigree 1: Albinism
Is this trait dominant or recessive? Give the evidence from the pedigree. (2 marks)
Explain why this trait cannot be X-linked recessive.
Give the genotypes of I-1, I-2 and II-2 (use A and a).
II-1 is unaffected. What is the probability that she is a carrier (Aa)?
What is the probability that the next child of II-3 and II-4 will be affected?
Part C – Pedigree 2: Huntington's Disease
Is this trait dominant or recessive? Give the evidence from the pedigree. (2 marks)
Explain why this trait cannot be X-linked dominant.
Give the genotypes of I-2 and II-2.
What is the probability that the next child of II-1 and II-2 will be affected?
What is the probability that the next child of II-4 and II-5 will be affected?
Part D – Pedigree 3: Haemophilia
What is the most likely inheritance pattern? Give two clues. (2 marks)
Give the genotypes of I-2 and II-3 (use XH and Xh).
II-2 is unaffected. What is the probability that she is a carrier?
What is the probability that the next son of II-3 and II-4 will be affected?
Part E – Draw a Pedigree
Draw the pedigree. Two unaffected parents have three children: an affected son, an unaffected son and an unaffected daughter. The daughter has a child with an unaffected man, and they have one affected daughter. Number the generations and individuals. (2 marks)
Part F – Spot the Mistake
A student says: “The trait skips generation II, so it must be dominant.” Explain the error and correct it.
A student says: “Only males are affected in this family, so the trait must be on the Y chromosome.” Explain the error and correct it.
Pedigree Worksheet Answer Key
Open each part of the pedigree worksheet answers to check your work. The printable key, including the drawn answer to Part E, is at the end of the PDF.
Part A answers (Q1–6)
Affected male
Unaffected female
Mating (couple) line
Affected female
Unaffected male
Carrier female
Part B answers (Q7–11)
Recessive. I-1 and I-2 are both unaffected but have an affected son (II-2), so they must carry a hidden allele.
III-2 is an affected daughter with an unaffected father (II-3). An X-linked recessive daughter must get an affected X from her father.
I-1 Aa, I-2 Aa, II-2 aa
Of the unaffected outcomes (AA, Aa, Aa), two are carriers: 2/3
They already have an affected child, so both are Aa: 1/4
Part C answers (Q12–16)
Dominant. II-4 and II-5 are both affected but have an unaffected daughter (III-4), so both must be Aa and the affected allele is dominant.
Affected son II-4 has an unaffected mother (I-2). A son gets his X only from his mother, so the trait cannot be X-linked dominant.
I-2 aa (unaffected); II-2 Aa (affected, with an unaffected mother)
aa × Aa: 1/2
Aa × Aa: P(A_) = 3/4
Part D answers (Q17–20)
X-linked recessive. Only males are affected, and affected sons (II-1, III-1) have unaffected parents, so the allele passes through carrier mothers.
Both are carriers: XHXh (each has an affected son)
Her mother is XHXh and her father XHY: 1/2
Sons get the mother’s X: 1/2
Part E answer (Q21)Part F answers (Q22–23)
Skipping a generation is a sign of a recessive trait: unaffected carriers pass it on without showing it.
A Y-linked trait would pass from every affected father to all his sons. Mostly-male patterns with unaffected fathers point to X-linked recessive inheritance.
5 Common Pedigree Mistakes
"It skips a generation, so it's dominant." Skipping generations points to a recessive trait.
Forgetting the 2/3 rule. An unaffected child of two carriers has a 2/3 (not 1/2) chance of being a carrier.
Assuming mostly-male means Y-linked. Y-linked traits pass from father to every son; X-linked traits pass through mothers.
Mixing up generations and individuals. Roman numerals are generations; ordinary numbers are people.
Guessing without evidence. Always name the specific family members that prove the pattern.
How to Use This Pedigree Worksheet in Class
Lesson 1: Parts A and B of the pedigree worksheet, modelling the "unaffected parents, affected child" test.
Lesson 2: Parts C–F, then have students swap their Part E drawings and check each other's work.
Extension: Students research a real genetic condition and draw a sample family pedigree for it.
Yes. The worksheet and its answer key are free to download and print as a PDF, with no account needed.
How do you tell if a pedigree is dominant or recessive?
If two unaffected parents have an affected child, the trait is recessive. If two affected parents have an unaffected child, the trait is dominant.
How can you tell if a trait is X-linked?
X-linked recessive traits mostly affect males, usually pass from carrier mothers to sons, and never pass from father to son. An affected daughter must have an affected father.
What do the symbols on a pedigree mean?
Squares are males and circles are females. Shaded symbols are affected, and a dot shows a carrier. A horizontal line joins a couple, and a vertical line leads down to their children.
What grade is this pedigree worksheet for?
It is written for Grade 11 biology (the Genetic Processes unit) and also works as review for Grade 12 biology.
Ready to start? Download the free pedigree worksheet PDF (use the Download button above), print it double-sided, and keep the answer key pages for marking.