👤 By the CinnaEntry Content Team🕐 Updated 2026-09-06🏷️ HESI Biology🔖 Free to read, print, and share
Also known as: punnett square · genotype · phenotype · dominant · recessive · allele
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Use this one-page guide to lock in Genetics Cheat Sheet for the ATI TEAS 7 and HESI A2. Keep it handy during review and on exam day.
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📒 The 1-minute cheat sheet
📌 The Words
Allele — one version of a gene (B or b)
Genotype — the letters (BB, Bb, bb)
Phenotype — what you can SEE
Homozygous = same pair · Heterozygous = different pair
📌 Bb × Bb
Boxes: BB, Bb, Bb, bb
Genotype ratio 1 : 2 : 1
Phenotype ratio 3 dominant : 1 recessive
Recessive trait appears ONLY as bb
📚 Genetics Cheat Sheet — full study notes
The cheat sheet above is your quick recall card. These notes go deeper — what it is, what to do first, what must be reported, and what to teach.
Genetics questions on the HESI stay at the level of one trait and two alleles. If you can set up a 2×2 square and read the ratio off it, you can answer nearly all of them.
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Key points
Understand these first
An ALLELE is one version of a gene. A capital letter is dominant, a lowercase letter is recessive.
GENOTYPE is the letter combination (BB, Bb, bb); PHENOTYPE is the trait you can actually observe.
Homozygous means two identical alleles (BB or bb); heterozygous means two different ones (Bb).
A recessive trait only appears when BOTH alleles are recessive (bb).
Bb × Bb gives a genotype ratio of 1 BB : 2 Bb : 1 bb, and a phenotype ratio of 3 dominant : 1 recessive.
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Study first
Where to start
Cross Bb × Bb: put one parent's alleles across the top and the other's down the side, fill the four boxes, and you get BB, Bb, Bb, bb — three of the four show the dominant trait.
Two brown-eyed parents can have a blue-eyed child if both are Bb: the bb box is one in four.
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Red flags — report now
Escalate immediately
Confusing genotype and phenotype. Bb and BB LOOK the same but are written differently — that difference is the whole question.
Reading the 3:1 phenotype ratio as a genotype ratio; the genotype ratio is 1:2:1.
Assuming a dominant allele is more common in a population — dominant describes which allele is expressed, not how frequent it is.
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Commonly tested
What comes up most
Always draw the square, even when the answer seems obvious. Four boxes take ten seconds and remove all guesswork.
Write the phenotype under each box as you fill it. The ratio then reads straight off the grid.
❓ Genetics Cheat Sheet: TEAS & HESI FAQs
What should I focus on first when studying Genetics Cheat Sheet?
Cross Bb × Bb: put one parent's alleles across the top and the other's down the side, fill the four boxes, and you get BB, Bb, Bb, bb — three of the four show the dominant trait. Two brown-eyed parents can have a blue-eyed child if both are Bb: the bb box is one in four.
What are the warning signs of Genetics Cheat Sheet a nurse must report?
Confusing genotype and phenotype. Bb and BB LOOK the same but are written differently — that difference is the whole question. Reading the 3:1 phenotype ratio as a genotype ratio; the genotype ratio is 1:2:1. Assuming a dominant allele is more common in a population — dominant describes which allele is expressed, not how frequent it is.
What do I need to know about Genetics Cheat Sheet for the TEAS or HESI?
An ALLELE is one version of a gene. A capital letter is dominant, a lowercase letter is recessive. GENOTYPE is the letter combination (BB, Bb, bb); PHENOTYPE is the trait you can actually observe. Homozygous means two identical alleles (BB or bb); heterozygous means two different ones (Bb). A recessive trait only appears when BOTH alleles are recessive (bb).
What are the most commonly tested points on Genetics Cheat Sheet?
Always draw the square, even when the answer seems obvious. Four boxes take ten seconds and remove all guesswork. Write the phenotype under each box as you fill it. The ratio then reads straight off the grid.
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Quick Tip
An ALLELE is one version of a gene. A capital letter is dominant, a lowercase letter is recessive.