An ALLELE is one version of a gene. A capital letter is dominant, a lowercase letter is recessive.
Before you read
Test yourself first: 1 question
Question 1 of 1
The study of heredity and how traits are passed on is called:
Answer: B. Genetics is the study of genes, heredity, and variation in organisms.
Keep the streak going with more questions like these, each with a full rationale.
Key points
- 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.
Study first
- 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.
Commonly tested
- 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.
Watch out for
- 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.
Genetics Cheat Sheet: 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 is most often missed on Genetics Cheat Sheet?
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 HESI A2?
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.
