Biology Unit 6 Vocab

Interphase

The longest phase of the cell cycle (G1, S, G2) where the cell grows, copies its DNA, and prepares for division.

S Phase

The synthesis phase of the cell cycle where DNA replication occurs.

Cancer

A disease caused by uncontrolled cell division and the failure of normal cell cycle checkpoints.

Apoptosis

Programmed cell death; a mechanism used to eliminate damaged or abnormal cells before they divide.

Proto-oncogene

A normal gene that promotes cell division (like a 'gas pedal'). When mutated, it becomes an oncogene and causes cells to divide continuously.

Tumor Suppressor Gene

A gene that slows down cell division, repairs DNA mistakes, or initiates apoptosis (like the 'brakes').

Mitosis

Cell division resulting in two identical diploid somatic (body) cells. Used for growth and repair.

Meiosis

Cell division resulting in four genetically unique haploid gametes (sex cells). Used for reproduction.

Gamete

A reproductive/sex cell (sperm or egg) that contains a single set of chromosomes (haploid).

Somatic cell

Any cell of a living organism other than the reproductive cells (e.g., skin, bone, muscle). These are diploid.

Zygote

A diploid cell resulting from the fusion of two haploid gametes (a fertilized egg).

Diploid (2n)

A cell containing two complete sets of chromosomes, one from each parent.

Haploid (n)

A cell having a single set of unpaired chromosomes.

Mitotic Index

The ratio of the number of cells undergoing mitosis to the total number of cells in a population. High index = rapid division.

Allele

One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

Genotype

The genetic makeup of an organism; the specific combination of alleles it possesses (e.g., AA, Aa, aa).

Phenotype

The observable physical properties or traits of an organism, determined by its genotype and environment.

Heterozygous

Having two different alleles for a particular gene (e.g., Rr).

Homozygous

Having two identical alleles for a particular gene (e.g., RR or rr).

Autosomal Recessive

A trait where TWO copies of the mutated gene (one from each parent) are needed to cause the disorder.

Mutation

A change in the DNA sequence of an organism, which can result from errors during replication or environmental factors.

Codominance

A genetic scenario where neither allele is recessive, and both are fully and equally expressed (e.g., Roan coat in cattle).

Crossing Over

The exchange of genetic material between homologous chromosomes during Prophase I of meiosis, increasing genetic diversity.

Independent Assortment

The random alignment and distribution of maternal and paternal chromosomes during Metaphase I of meiosis.

Nondisjunction

The failure of chromosomes to separate properly during meiosis, leading to an abnormal number of chromosomes in gametes.

Karyotype

An individual's complete set of chromosomes, often displayed as a visual profile to look for abnormalities.