Heredity and Genetics: Key Concepts in Biology

Genome

The complete set of genetic material (all DNA) in an organism.

Chromosome

A thread-like structure made of DNA and proteins that carries genetic information. Humans have 46 chromosomes (23 pairs).

Gene

A segment of DNA that contains instructions to make a protein or perform a function.

DNA (Deoxyribonucleic Acid)

The molecule that stores genetic information; built from nucleotides in a double-helix structure.

Nucleotide

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

Allele

Different versions of the same gene (e.g., allele for blue eyes vs. allele for brown eyes).

Trait

A physical or behavioral characteristic determined by genes (and sometimes environment), like eye color or height.

Dominant

An allele that shows its effect even if only one copy is present (e.g., brown eyes allele).

Recessive

An allele that is hidden unless two copies are present (e.g., blue eyes allele).

Homozygous

Having two identical alleles for a gene (AA or aa).

Heterozygous

Having two different alleles for a gene (Aa).

Phenotype

The observable traits or characteristics of an organism (what you see).

Genotype

The genetic makeup of an organism (the actual alleles present).

Made of cells

The basic unit of life.

Use energy

For growth, repair, and daily functions.

Grow and develop

Change over time.

Reproduce

Make new organisms (asexual or sexual).

Respond to environment

React to stimuli like light, temperature, or food.

Maintain homeostasis

Keep internal conditions stable (like body temperature).

Evolve over time

Populations of living things can change through generations.

Gene expression

The process where different genes are turned on or off in different cell types.

Transcription

The process where a temporary RNA copy of a gene is made so the instructions can leave the nucleus and be used to make a protein.

RNA Processing

The modification of raw mRNA (pre-mRNA) in the nucleus to create a mature mRNA with a cap, tail, and no introns, preparing it for translation.

Translation

The process occurring in the cytoplasm at the ribosome where mRNA, tRNA, and amino acids are used to build a polypeptide (protein chain).

Substitution (Point Mutation)

A type of DNA mutation where one base is replaced by another (e.g., A → G).

Insertion

A type of DNA mutation where one or more bases are added into the DNA sequence.

Deletion

A type of DNA mutation where one or more bases are removed from the DNA sequence.

Beneficial Mutation

A mutation that improves the organism's traits or survival, which is rare but drives evolution.

Neutral Mutation

A mutation that has no effect on the organism's traits or functions.

Harmful (Deleterious) Mutation

A mutation that negatively affects the organism, potentially causing diseases or malfunctions.

Law of Segregation

Mendel's law stating that each organism carries two alleles for each trait, but only one is passed to offspring.

Law of Independent Assortment

Mendel's law stating that genes for different traits are inherited independently of one another.

Law of Dominance

Mendel's law stating that in a heterozygote, one allele may mask the expression of another (dominant vs. recessive).

Allele Inheritance

One allele per gene is passed from each parent, resulting in two alleles per gene for the offspring.

Genetic Variation

The diversity in gene frequencies within a population, achieved through mutations, independent assortment, crossing over, sexual reproduction, and gene flow.

Importance of Genetic Variation

Genetic variation increases survival by allowing populations to adapt, drives evolution through natural selection, reduces the risk of genetic diseases, and contributes to biodiversity.

Crossing Over (Recombination)

The exchange of DNA between homologous chromosomes during meiosis, contributing to genetic variation.

Sexual Reproduction

The process of combining alleles from two parents, which contributes to genetic variation.

Gene Flow

The movement of genes between populations, which can affect genetic variation.

Raw mRNA (pre-mRNA)

The initial form of mRNA that undergoes processing to become mature mRNA.

Mature mRNA

The processed form of mRNA that includes a cap, tail, and no introns, ready for translation.

Polypeptide

A chain of amino acids that forms a protein, created during the translation process.

Ribosome

The cellular structure in the cytoplasm where translation occurs, synthesizing proteins from mRNA.