Released STAAR Biology EOC · 2025 · Item 27 · 1 point

Walkthrough: Biology 2025, Item 27

B.8B · Genetic Crosses · unscored study

A family diagram. Grandparent 1 does not have Marfan syndrome and Grandparent 2 has it; they are the parents of Parent 1, who does not have Marfan syndrome. Grandparent 3 has Marfan syndrome and Grandparent 4 does not; they are the parents of Parent 2, who has Marfan syndrome. Parents 1 and 2 are the parents of Child 1, marked with a question mark. — Family affected by Marfan syndromeOriginal visual from the released STAAR test.

Marfan syndrome is an autosomal dominant disorder that affects connective tissue in the skeletal system and skin. The figure shows a family affected by Marfan syndrome. What is the probability that Child 1 will have Marfan syndrome?

25%
50%
75%
100%

1. Understand the question

Marfan syndrome is autosomal dominant. Find each parent's genotype, then the child's probability.

Try the question on your own first, then reveal one step at a time.

2. Solve it step by step

Practice released items for this skill Back to the lesson

Question, artwork, answer key and rationale: Texas Education Agency released STAAR test. Walkthrough steps written by TEKSForge. Studying here does not change your mastery or scores.