A: 15% of the human genome
Q: What is a homeobox?
A: A 180-nucleotide sequence that specifies a 60-amino-acid homeodomain in the encoded proteins.
Q: What are multigene families?
A: Collections of two or more identical or very similar genes.
1. New approches have accelerated the pace of genome sequencing
2. Scientists use bioinformatics to analyze genomes and their functions.
3. Genomes vary in size, number of genes, and gene density.
4. Multicellular eukaryotes have much noncoding DNA and many multigene families.
5. Duplication, rearrangement, and mutation of DNA contribute to genome evolution.
Figure 21.12
Gene duplication due to unequal crossing over.
One mechanism by which a gene can be duplicated is recombination during meiosis between copies of a transposable element flanking the gene. Such recombination between misaligned nonsister chromatids of homologous chromosomes produces one chromatid with two copies of the gene and one chromatid with no copy.
The sequencing of the human genome has been seen as the most ambitious mapping project. It officially began as the Human Genome Project in 1990, in major, going through three stages: genetic mapping, physical mapping, and DNA sequencing. Humans have 20,488 genes and we can make 75,000 polypeptides. Humans and other mammals have the lowest gene density and the number of genes is not correlated to genome size.
It seems that the rate of duplications and inversions have accelerated about 100 million years ago.
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