chapter 15

A is the full complement of genetic information of an organism, usually obtained by the entire DNA of an individual.
- • DNA sequencing
  1. The unknown single-stranded DNA is used as a template to synthesize a complementary chain using DNA polymerase, primer, the 4 nucleotides and also 4 modified nucleotides (C, G, T, A).
  2. The modified nucleotides stop extension of the new chain at different points, allowing separation of the different-sized fragments by gel electrophoresis.
  continue Tutorial:
- • DNA sequencing (continued)
  1. The gel can be analyzed by a computer.
  2. The sequence of the new chain is displayed.
The genome consist of almost 99% non-coding DNA.
- • The human genome contains only about 1% protein-encoding genes.
  The rest consists of:
  - Introns are non-coding DNA interspersed between segments of exons.
  - Duplicated and repeated sequences are short DNA sequences that are repeated many times.
  - Structural DNA are highly condensed around the centromere and are untranscribed.
  - Transposable elements are DNA sequences that can "jump" between chromosomes, leading to transpositions.
Large genomes often arise through of chromosomes or entire genomes.
- • Most vertebrates have similar genome sizes, except for some fish such as pufferfish.
  Many plants also have more genes than animals.
- • Genome duplication.
  The large genome size of the pufferfish is mainly due to duplication of genes.
  The pufferfish shares many genes with humans; some of its genes have been duplicated.
  Presumably humans and pufferfish descended from a common ancestor and inherited the common genes.
Genomic similarity among species reflects relatedness.
- • The closest relative to humans in terms of nucleotide sequence similarity in the genome is the chimpanzee ( a great ape): our genomes are 91% similar. Humans are more distantly related to amphibians such as frogs and pufferfish such as Fugu.
- • Genome divergence
  The genome similarity among vertebrates matches well with proposed divergence timelines from fossil evidence.
  Humans share a more recent common ancestor with apes (Chimpanzee) and monkeys than more distant mammalian relatives, monotremes (mammals that lay eggs).
  Our common ancestor with pufferfish are even more distant, reflecting our genome similarity of 2%.
Gene can be used to study patterns of gene expression of an organism.
- • This gene microarray contains hundreds of thousands of single-stranded DNA on a glass chip.
  This chip represents all the known alleles in the human genome.
  DNA from an individual is denatured and hybridized to the array to analyze that person's genotype.