CH 21

• Genome: entire set of DNA instructions found in a cell The instructions are required for the development and functions of organisms
• Craig Venter used cloning and sequencing of fragments of randomly cut DNA followed by assembly into a single continuous sequence
• Genomics is the study of whole sets of genes and their interactions
• The NCBI BLAST:

  A specific DNA sequence

  ▪ A predicted protein sequence

  ▪ Common stretches of amino acids in a protein

  ▪ Three-dimensional protein structures

  ▪ And compare a DNA sequence in GenBank, baseby base
• Genomes of most bacteria and archaea range from 1 to 6 million base pairs (Mb)
• Free-living bacteria and archaea have 1,500 to 7,500 genes
• humans have 3,000 Mb (million base pairs)
• Humans and other mammals have the lowest gene density, or number of genes, in a given length of DNA
• Noncoding DNA found between genes includes

  • Repetitive DNA, present in multiple copies in the genome

  • Pseudogenes, former genes that have accumulated mutations and are nonfunctional
• The basis of change at the genomic level is mutation, which underlies much of genome evolution
• Accidents in meiosis can lead to one or more extra sets of chromosomes, a condition known as polyploidy
• Unequal crossing over during prophase 1 of meiosis can result in one chromosome with a deletion and another with a duplication of a particular region
• Transposable elements can provide sites for crossover between non-sister chromatids
• transposable elements may carry a gene or groups of genes to a new position

  Multiple copies of similar transposable elements facilitate recombination, or crossing over, between different chromosomes
• insertion of transposable elements within a protein-coding sequence may block protein production
• The rest of the genes occur in multigene families, collections of two or more identical or very similar gene
• Humans have 23 pairs of chromosomes, while chimpanzees have 24 pairs
• One copy of a duplicated gene can undergo alterations that lead to a completely new function for the protein product
• Lysozyme is an enzyme that helps protect animals against bacterial infection
• Highly conserved genes have changed very little over time
• Homeotic genes in animals are called Hox genes

  • Hox genes encode transcription factors with a DNA- binding domain called a homeo box, and regulate development of body plan
• Colored bands represent homeotic genes and correspond to same color body regions
• epigenetics: Affect gene expression without changing the sequence of nucleotides bases