Fundamentals of DNA, Genetics, and Inheritance

DNA

Made of four bases (A, T, C, G) that form base pairs (A-T, C-G); the instructions for life.

Genome

A complete set of DNA instructions; in humans, it consists of ~3.2 billion base pairs.

Nucleus

The part of the cell where DNA is stored.

Nucleosomes

Structures formed by DNA wrapped around proteins (histones) to help fit in the nucleus.

Chromosomes

Organized structures of DNA; humans have 46 chromosomes in total (23 pairs).

Genes

Specific sections of DNA that code for proteins.

Alleles

Different versions of genes.

Exons

Coding parts of genes that are used for proteins.

Introns

Non-coding parts of genes that are removed.

mRNA

Messenger RNA that is transcribed from DNA in the nucleus and translated into proteins at the ribosome.

Proteins

Made of amino acids; perform most of the work in cells including enzymes, hormones, and muscle structure.

Amino Acids

20 types of building blocks for proteins, obtained from food and reused by the body.

Mutation

A change in the DNA sequence that can be helpful, harmful, or neutral.

Genetic Variation

Differences in DNA among individuals, often resulting from mutations.

Traits

Physical, behavioral, or biochemical features of an organism.

Inherited Traits

Traits passed down through DNA (e.g., eye color, hair type).

Acquired Traits

Traits learned or influenced by the environment (e.g., language, scars).

Identical Twins

Twins that have the exact same DNA but can be shaped differently by their environments.

1st Law of Segregation

Each parent gives one allele to their offspring.

2nd Law of Independent Assortment

Genes for different traits are inherited independently.

Dominant Alleles

Alleles that only need one copy to be expressed.

Recessive Alleles

Alleles that need two copies to be seen.

Homozygous

Having two identical alleles (AA or aa).

Heterozygous

Having two different alleles (Aa).

Phenotype

The physical appearance of an organism (e.g., blue eyes).

Genotype

The genetic makeup of an organism (e.g., Bb, aa).

Punnett Squares

Tools used to predict the probability of offspring traits.

Monohybrid Cross

A genetic cross involving one trait.

Dihybrid Cross

A genetic cross involving two traits.

DNA Replication

The process by which DNA makes a copy of itself before a cell divides.

S Phase

The phase of the cell cycle where DNA replication occurs.

Semi-Conservative Replication

DNA replication method where one old strand and one new strand are in each new DNA molecule.

Anti-Parallel Strands

DNA strands that run in opposite directions.

Recombination

The process during meiosis where chromosomes can swap parts, increasing genetic diversity.

Gel Electrophoresis

A technique that separates DNA fragments by size, used in forensics and research.

Sex Chromosomes

X and Y chromosomes that determine sex (XX = female, XY = male).

Diploid Cells

Cells that have two sets of chromosomes.

Haploid Cells

Gametes that have one set of chromosomes.

Gene Expression

The process of converting DNA into RNA and then into proteins.

Complex Inheritance Patterns

Inheritance patterns that can include incomplete dominance or polygenic inheritance.

DNA (Deoxyribonucleic Acid)

A molecule made of nucleotides (A, T, C, G); stores genetic instructions for building proteins.

Nucleotide

The building block of DNA; made of a sugar, a phosphate, and a nitrogen base (A, T, C, G).

Base Pairs

A pairs with T, C pairs with G; these pairs form the rungs of the DNA double helix.

Anti-parallel

The two strands of DNA run in opposite directions.

Chromosome

Tightly coiled DNA found in the nucleus; humans have 23 pairs (46 total).

Gene

A stretch of DNA that codes for a protein or RNA; controls traits.

Allele

A different version of a gene (e.g., blue eyes vs. brown eyes).

Genotype

The genetic makeup of an organism (ex: Aa, BB).

Phenotype

The physical appearance or behavior (ex: blue eyes, curly hair).

Mutation

A change in the DNA sequence; can be beneficial, harmful, or neutral.

Exon

The coding region of a gene used to build proteins.

Intron

Non-coding regions within a gene that are removed before translation.

Switches

Regulatory DNA sequences that tell genes when to turn on/off.

Nucleosome

DNA wrapped around histone proteins; helps condense DNA.

DNA Replication

The process of copying DNA during the S phase. Uses enzymes and is semi-conservative (one old strand + one new).

RNA (Ribonucleic Acid)

A single-stranded molecule that carries instructions from DNA to ribosomes.

Transcription

DNA is copied into messenger RNA in the nucleus.

Translation

RNA is read by ribosomes to assemble amino acids into proteins.

Amino Acid

Monomer of proteins; 20 different kinds used in various combinations.

Protein

A molecule made of amino acids; does most work in the body: enzymes, hormones, muscles, receptors, transporters, defense, structure.

Ribosome

The site of protein synthesis.

Codon

A sequence of 3 RNA bases that codes for one amino acid.

Heredity

Passing of traits from parents to offspring via DNA.

Trait

A characteristic of an organism, such as eye color, height, or behavior.

Inherited Trait

Passed from parents through DNA (ex: eye color).

Acquired Trait

Gained from environment or experiences (ex: language, scars).

Homozygous

Two of the same alleles (ex: AA or aa).

Heterozygous

Two different alleles (ex: Aa).

Dominant

An allele that shows its effect with only one copy.

Recessive

An allele that needs two copies to show its effect.

Law of Segregation

Each parent gives one allele for each trait.

Law of Independent Assortment

Genes for different traits are passed independently.

Punnett Square

A tool to predict the probability of inheritance.

Monohybrid Cross

Cross involving one trait (e.g., Aa × Aa).

Dihybrid Cross

Cross involving two traits (e.g., AaBb × AaBb).

Sex Chromosomes

Determine biological sex (XX = female, XY = male).

Gametes

Sex cells (sperm and egg); haploid (contain 1 set of chromosomes).

Diploid

Normal cells with 2 sets of chromosomes.

Gregor Mendel

"Father of Genetics," studied pea plants and discovered patterns of inheritance.

True Breeding

Organisms that always pass down certain traits.

Gel Electrophoresis

Lab technique that separates DNA fragments by size.

Variation

Differences in traits due to genetic and environmental factors.

Recombination

Chromosome segments are swapped between homologous chromosomes during meiosis → increases diversity.

Humans share 99.9% of their DNA

Small variations make us unique.

A full DNA strand in one human cell

~3 feet long.

DNA → RNA → Protein

Central Dogma of biology. Traits can be polygenic (controlled by many genes) or influenced by environment.

Mutations

Raw material for evolution.

Protein jobs

enzymes, protections, muscle fibers, defense, receptors, transport, structure, hormones, etc.

3rd Law of dominance

Only one dominant copy is necessary to have one dominant appearance.

Outside letters of the Punnett square

Represent the segregation of alleles into gametes of the parents