Pedigree Analysis APBiology KEY 1 ... - Free Printable

The image you've uploaded is a pedigree practice worksheet for AP Biology, with several pedigree charts and corresponding questions about genetic inheritance patterns. The worksheet includes five different genetic disorders: Maple Syrup Urine Disease (MSUD), Leber Congenital Amaurosis (LCA), Marfan Syndrome, Charcot-Marie-Tooth disease (CMT), and Cystic Fibrosis.

Below is a detailed explanation of each question and its solution, based on the answers provided in red (which appear to be the key), along with reasoning:

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1. Maple Syrup Urine Disease (MSUD)

Question 1: What is the inheritance pattern of this gene?
✔ Answer: b) autosomal recessive

Reasoning:
- Both parents are unaffected (not shaded), but they have an affected child (shaded). This means both parents must be carriers (heterozygous, Aa), and the child inherited two recessive alleles (aa).
- This is a classic hallmark of autosomal recessive inheritance: unaffected parents can have an affected child only if both carry the recessive allele.

Question 2: Provide at least one piece of evidence for your claim.
✔ Answer: Two parents that do not have the disease must be carriers (Aa) to have a child with the disease.

Explanation:
In autosomal recessive disorders, individuals need two copies of the mutant allele (aa) to express the disease. Since both parents are unaffected (phenotypically normal), they must each carry one copy of the mutated allele (Aa) to pass it on to an affected child.

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2. Leber Congenital Amaurosis (LCA)

Question 3: What is the inheritance pattern shown?
✔ Answer: autosomal recessive

Reasoning:
- Affected individuals (shaded) appear in multiple generations.
- Unaffected parents (Aa × Aa) produce affected offspring (aa), indicating both parents are carriers.
- There’s no male-to-male transmission, which rules out X-linked inheritance.
- The trait skips generations — consistent with recessive inheritance.

Question 4: Highlight one individual whose genotype is unknown. What additional information would you need to determine his/her genotype?

✔ Answer: One individual labeled "A?" (e.g., the male in generation II, left side).

Explanation:
- This individual is unaffected, so he could be either AA or Aa.
- To determine if he's a carrier (Aa), we'd need to know whether any of his offspring have the disease.
- If he has children with an unaffected partner and they have an affected child, then he must be a carrier (Aa).
- If all children are unaffected and no family history, he might still be a carrier but we cannot confirm without more data.

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3. Marfan Syndrome

Question 5: What is the inheritance pattern shown?
✔ Answer: autosomal dominant

Reasoning:
- Affected individuals have at least one affected parent (except possibly for de novo mutations).
- The trait appears in every generation (no skipping).
- Individuals who are unaffected (aa) do not pass the trait to their children — this confirms it’s dominant.
- Even though some children (like 1,2,3) are unaffected, they are not carriers because the trait is dominant, not recessive.

Question 6: Provide at least one piece of evidence for your claim.
✔ Answer: The first two parents both had Marfan syndrome, but had children who did not have the disorder.

Explanation:
This shows that the trait is dominant:
- Parents with the disease (Aa) can have unaffected children (aa) if they pass on the normal allele.
- If it were recessive, both parents would have to be aa, and all children would be affected — which isn’t the case.

Question 7: Consider the children labeled “1,2,3.” Would you expect any of these individuals to have children of their own with Marfan Syndrome?

✔ Answer: No — anyone without the syndrome must be recessive (aa), so they cannot pass on the dominant allele.

Explanation:
Since Marfan syndrome is autosomal dominant, only those with at least one copy of the mutant allele (A) will show the trait. Individuals 1, 2, and 3 are unaffected → genotype = aa → they cannot pass on the disease allele. Therefore, their children will be normal unless there's a new mutation.

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4. Charcot-Marie-Tooth disease (CMT)

Question 8: What is the inheritance pattern shown?
✔ Answer: X-linked recessive

Reasoning:
- More males are affected than females.
- Affected fathers do not pass the trait to sons (because sons get Y from father, not X).
- Affected males pass the allele to all daughters (who become carriers).
- Females can be carriers without showing symptoms.

Question 9: Provide at least one piece of evidence for your claim.
✔ Answer: The disease mainly affects boys, though a girl can have it if her father had it and her mother was a carrier.

Explanation:
- In X-linked recessive disorders:
- Males (XY) are more likely to be affected because they have only one X chromosome.
- A female needs two copies of the mutant allele (one from each parent) to be affected.
- So, if a daughter inherits the mutant allele from her father (who has CMT) and a carrier mother (X^A X^a), she can be affected.

Question 10: The dashed line represents a possible union. Discuss the probability that such a union would result in a child with CMT.

✔ Answer:
- The father is affected (X^a Y), so he passes X^a to daughters and Y to sons.
- The mother is a carrier (X^A X^a), so she passes either X^A or X^a with 50% chance.

Probabilities:
- Daughter (XX):
- 50% chance of X^a X^a → affected
- 50% chance of X^A X^a → carrier (but not affected)
- Son (XY):
- 50% chance of X^a Y → affected
- 50% chance of X^A Y → normal

So, each child has a 50% chance of being affected, regardless of sex.

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5. Cystic Fibrosis

Question 11: What is the inheritance pattern shown?
✔ Answer: autosomal recessive

Reasoning:
- Unaffected parents (Aa × Aa) produce affected children (aa).
- The trait skips generations.
- Both sexes are equally affected.
- This matches autosomal recessive inheritance.

Question 12: Provide at least one piece of evidence for your claim.
✔ Answer: Two parents that do not have the disease must be carriers (Aa) to have a child with the disease.

Explanation:
Same logic as MSUD and LCA — for a child to be affected (aa), both parents must contribute a recessive allele. Since the parents are unaffected, they must be heterozygous carriers (Aa).

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✔ Summary Table of Inheritance Patterns:

| Disorder | Inheritance Pattern | Key Evidence |
|--------|---------------------|-------------|
| MSUD | Autosomal Recessive | Unaffected parents have affected child |
| LCA | Autosomal Recessive | Same as above; skip generations |
| Marfan Syndrome | Autosomal Dominant | Affected individuals have affected parents; unaffected individuals never pass it on |
| CMT | X-linked Recessive | More males affected; father-to-daughter transmission |
| Cystic Fibrosis | Autosomal Recessive | Carrier parents produce affected child |

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🔍 General Tips for Pedigree Analysis:

1. Autosomal Recessive:
- Affected individuals often have unaffected parents.
- Skips generations.
- Equal sex distribution.

2. Autosomal Dominant:
- Appears in every generation.
- Affected individuals usually have at least one affected parent.
- Unaffected individuals do not pass the trait.

3. X-linked Recessive:
- More males affected.
- Affected males pass allele to all daughters (carriers).
- Never passed from father to son.
- Carrier mothers may have affected sons.

4. X-linked Dominant:
- Rare; affects more females.
- Affected father passes to all daughters, none to sons.
- Not seen here.

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Let me know if you’d like this converted into a printable study guide or need help drawing genotypes for specific individuals!