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HESI A2 Biology: Genetics practice questions

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These are original practice items written to the HESI A2 blueprint (4 options, no penalty for wrong answers), not actual exam questions. Try each one before you open the answer.

What this topic covers

Biology: Genetics sits inside the Biology section of the HESI A2. Our bank holds 55 verified items tagged to it, and the 4 below are a fixed sample so the page stays the same every time you open it. Each one shows the reasoning, not just the letter.

The topic tag comes from our own items rather than from a published syllabus, so treat it as a map of what we cover. For the official section breakdown see the HESI A2 page.

Biology: Genetics sample questions

Question 1

In a pedigree analysis, a trait appears in every generation and affects both males and females equally. Which pattern of inheritance is most likely?

  1. A X-linked recessive
  2. B Mitochondrial
  3. C Autosomal recessive
  4. D Autosomal dominant
Show the answer and explanation

Correct answer: D

Autosomal dominant traits do not skip generations and affect males and females equally because the gene is on a non-sex chromosome and only one copy is needed for expression.

Why the other options are wrong:
A: X-linked recessive traits are more common in males and can skip generations through carrier females.
B: Mitochondrial inheritance is maternal, affecting both sexes but only passed from mothers, not appearing equally in every generation.
C: Autosomal recessive traits often skip generations because carriers are unaffected, and they affect both sexes equally but not every generation.

Question 2

In a certain plant, the allele for tall stems (T) is dominant over dwarf (t), and the allele for red flowers (R) is dominant over white (r). A dihybrid cross between two plants heterozygous for both traits yields 320 offspring. How many offspring are expected to be dwarf with white flowers?

  1. A 60
  2. B 80
  3. C 20
  4. D 180
Show the answer and explanation

Correct answer: C

A dihybrid cross (TtRr × TtRr) produces a 9:3:3:1 phenotypic ratio. Dwarf white flowers correspond to the double recessive (ttrr), which is 1/16 of the offspring. 320 × 1/16 = 20.

Why the other options are wrong:
A: 60 is 3/16 of 320, which would be the number for either dwarf red or tall white.
B: 80 is 1/4 of 320, which is not a single phenotype fraction in a 9:3:3:1 ratio.
D: 180 is 9/16 of 320, which corresponds to tall red (dominant for both traits).

Question 3

A man with hemophilia (X-linked recessive) marries a woman who is a carrier. What is the probability that their first son will have hemophilia?

  1. A 0%
  2. B 25%
  3. C 100%
  4. D 50%
Show the answer and explanation

Correct answer: D

The man has genotype XhY (hemophilia), and the woman is XHXh (carrier). Sons inherit Y from father and X from mother. The chance the son receives the Xh allele from his mother is 1/2, so 50% of sons will have hemophilia.

Why the other options are wrong:
A: 0% is incorrect because the mother is a carrier and can pass the affected allele.
B: 25% would be the probability if considering all children (including daughters), but the question specifically asks for the probability for a son.
C: 100% would only occur if the mother were affected (XhXh), which she is not.

Question 4

A pea plant heterozygous for tall stem (Tt) is crossed with a homozygous recessive short plant (tt). What is the probability of offspring being tall?

  1. A 25%
  2. B 75%
  3. C 50%
  4. D 100%
Show the answer and explanation

Correct answer: C

The cross Tt × tt produces offspring with genotypes Tt (tall) and tt (short) in a 1:1 ratio, so the probability of a tall offspring is 50%. A Punnett square shows that half of the offspring inherit the dominant T allele from the heterozygous parent.

Why the other options are wrong:
A: 25% would result from a cross of two heterozygous plants (Tt × Tt).
B: 75% would result from a cross of two heterozygous plants (Tt × Tt).
D: 100% would result only if the tall parent were homozygous dominant (TT).

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