Mishy Science Notes

02/03/2025

Genetics and DNA Cheat Sheet

This cheat sheet provides a quick overview of key concepts in genetics and DNA.

DNA (Deoxyribonucleic Acid): The molecule that carries genetic instructions for all known organisms.
Structure: A double helix, resembling a twisted ladder.
- Sides of the Ladder: Composed of sugar-phosphate backbones.
- Rungs of the Ladder: Composed of paired nitrogenous bases.
Nitrogenous Bases:
- Adenine (A) pairs with Thymine (T)
- Guanine (G) pairs with Cytosine (C)
Nucleotide: The basic building block of DNA, consisting of a sugar (deoxyribose), a phosphate group, and a nitrogenous base.
Genes: Segments of DNA that code for specific proteins or RNA molecules.
Genome: The complete set of genetic instructions for an organism.

Process: The process by which DNA makes a copy of itself.
Key Enzymes:
- DNA Helicase: Unwinds and separates the DNA double helix.
- DNA Polymerase: Adds new nucleotides to the growing DNA strand, following base-pairing rules.
- DNA Ligase: Joins fragments of DNA together.
Semi-conservative Replication: Each new DNA molecule contains one original strand and one newly synthesized strand.

RNA (Ribonucleic Acid): A molecule involved in protein synthesis.
Types of RNA:
- mRNA (messenger RNA): Carries the genetic code from DNA to the ribosomes.
- tRNA (transfer RNA): Carries amino acids to the ribosomes.
- rRNA (ribosomal RNA): A component of ribosomes.
Transcription: The process of copying a gene from DNA into mRNA.
- RNA Polymerase: The enzyme that synthesizes mRNA.
Translation: The process of using mRNA to synthesize a protein.
- Codon: A three-base sequence on mRNA that codes for a specific amino acid.
- Anticodon: A three-base sequence on tRNA that complements a codon on mRNA.
- Ribosomes: The cellular structures where translation occurs.

Chromosomes: Structures made of DNA and proteins that carry genes.
Humans: Have 46 chromosomes (23 pairs).
Mitosis: Cell division that produces two identical daughter cells. Used for growth and repair.
Meiosis: Cell division that produces four genetically different gametes (sex cells) with half the number of chromosomes. Used for sexual reproduction.

Alleles: Different versions of a gene.
Genotype: The genetic makeup of an organism (e.g., AA, Aa, aa).
Phenotype: The observable characteristics of an organism (e.g., eye color, height).
Dominant Allele: An allele that expresses its trait even when paired with a recessive allele.
Recessive Allele: An allele that expresses its trait only when paired with another recessive allele.
Punnett Square: A diagram used to predict the possible genotypes and phenotypes of offspring.
Mendel’s Laws of Inheritance:
- Law of Segregation: Alleles separate during gamete formation.
- Law of Independent Assortment: Genes for different traits are inherited independently of each other.

Mutation: A change in the DNA sequence.
Types of Mutations:
- Point Mutations: Changes in a single nucleotide.
  - Substitution: One base is replaced by another.
  - Insertion: An extra base is added.
  - Deletion: A base is removed.
- Frameshift Mutations: Insertions or deletions that shift the reading frame of the genetic code.
Causes of Mutations:
- Spontaneous: Errors during DNA replication.
- Induced: Caused by mutagens (e.g., radiation, chemicals).

Homozygous: Having two identical alleles for a gene (e.g., AA or aa).
Heterozygous: Having two different alleles for a gene (e.g., Aa).
Codominance: Both alleles are expressed equally in the phenotype.
Incomplete Dominance: The heterozygous phenotype is a blend of the two homozygous phenotypes.
Epigenetics: Changes in gene expression that are not due to changes in the DNA sequence itself.
Genetic Engineering: The direct manipulation of an organism’s genes.
Cloning: The process of creating a genetically identical copy of an organism or a gene.