Return to MCAT® Blog Homepage

MCAT Biology Question — Dihybrid Cross

For a particular plant, straight leaves result from a dominant gene (L) and wrinkled leaves result from a recessive gene (l), and tall height results from a dominant gene (T) while short height results from a recessive gene (t). A dihybrid cross is performed with plants heterozygous for both traits. What is the expected ratio of short, straight-leaved plants to tall, straight-leaved plants?


a) 1:1

b) 1:2

c) 1:3

d) 3:1



In a dihybrid cross, the genes for two traits are crossed in a Punnett square. For two heterozygotes crossed in a Punnett square, the expected ratio of recessive/recessive, dominant/recessive, recessive/dominant, to dominant is 1:3:3:9. In this particular question, the ratio of both recessive/dominant to dominant/dominant is 1:3.

new 4tests Punnett square

a) 1:1, incorrect.

b) 1:2, incorrect.

c) 1:3, correct, This ratio is shown above by the ratio of blue genotypes to orange genotypes.

d) 3:1, incorrect.

Want more MCAT practice?

We’ve got options for every schedule and learning style!

From the best online MCAT course created by top instructors with 524+ MCAT scores to the most representative full-length practice exams and private tutoring, we can custom tailor your MCAT prep to your goals!

Not sure which option is right for you? Schedule a free MCAT consultation with an MCAT expert using the form below. No obligation, just expert advice.

Create your Free Account to access our MCAT Flashcards SIGN UP NOW
MCAT is a registered trademark of the Association of American Medical Colleges (AAMC), which is not affiliated with Blueprint.