TEAS® Science Study Guide
DNA, RNA & Genetics
DNA vs. RNA
- DNA — Double helix (two strands). Stores genetic information. Base pairs: A–T and C–G. Contains the sugar deoxyribose.
- RNA — Single strand. Carries DNA’s instructions to build proteins. Uses uracil (U) instead of thymine, so its pairing is A–U and C–G. Contains the sugar ribose.
How genes become proteins
- Transcription — DNA’s code is copied into RNA.
- Translation — RNA’s code is read to build a protein.
DNA → RNA → protein. This is the central flow of genetic information.
Inheritance basics
- A gene is a segment of DNA that codes for a trait. Different versions of a gene are alleles.
- Dominant alleles (capital letter) mask recessive ones (lowercase). A recessive trait shows only when both alleles are recessive.
- Genotype is the genetic makeup (e.g., Bb). Phenotype is the physical trait you actually see (e.g., brown eyes).
- Homozygous means two identical alleles (BB or bb); heterozygous means two different ones (Bb).
Punnett squares
A Punnett square predicts the odds of offspring traits. Cross two heterozygous parents (Bb × Bb) and you get a 3:1 ratio — three offspring showing the dominant trait for every one showing the recessive. This 3:1 outcome is the single most-tested genetics result.
Terms to know
- Allele — A version of a gene.
- Genotype — The alleles present. Phenotype — The visible trait.
- Homozygous — Two matching alleles. Heterozygous — Two different alleles.
What the TEAS asks most
- Which base replaces thymine in RNA? Uracil.
- What are the DNA base pairs? A–T and C–G.
- Genotype vs. phenotype? Genotype is the genes; phenotype is the visible trait.
- What ratio results from crossing Bb × Bb? 3:1 dominant to recessive.