Chromosomes, Genes and Alleles:

Here’s a YouTube clip:

Let’s start with a tour of the basics from Learn.Genetics at Utah.

DNA coiling on histone proteins from biostudio.com

A description of chromosomes from Dexter Pratt

Zooming in to Chromosome 11 (a bit too advanced) from the DNA Learning Centre’s Gene Almanac

Transcription Java game from thinkquest.org
Mutations:

How do mutations occur? from the DNAi at the Dolan DNA Learning Centre

Evolution of Sickle Cell: Resistance to Malaria

Sickle Cell Anemia: A Mutation Story from the excellent Evolution Library.