25 June Genetics Variation and Change Introduction: DNA, alleles, genes and chromosones

DNA

A molecule that carries genetic information, structured as a double helix.

Chromosomes

Condensed strands of DNA and stabilizing proteins found in the cell nucleus.

Genes

Units of heredity that code for specific proteins.

Allele

A variation of a gene.

Structure of DNA

Composed of two strands wrapped around each other, forming a double helix.

Nucleotides

Monomers that make up DNA, consisting of sugar, phosphate, and a base.

Bases

Four types in DNA—Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).

Base pairing

A pairs with T, and C pairs with G in the DNA structure.

Sugar-phosphate backbone

The long chain formed by the bonding of phosphate to sugar in DNA.

Homologous chromosomes

Pairs of chromosomes that contain the same collection of genes but may have different alleles.

Diploid

Organisms, like humans, that have two sets of chromosomes (23 pairs).

Heterozygous

Having different alleles for a gene (e.g., blue eyes from one parent and brown from another).

Homozygous

Having identical alleles for a gene (e.g., blue eyes from both parents).

Locus

The specific position of a gene on a chromosome.