Haploid genome

The DNA in a eukaryotic genome can be divided into different sequence classes. These are unique-sequence, or nonrepetitive, DNA and repetitive-sequence DNA. In the haploid genome, unique-sequence DNA generally includes the single copy genes that code for proteins. The repetitive DNA in the haploid genome includes sequences that vary in copy number from two to as many as 10 copies per cell. 

Repetitive-sequence DNA can be broadly classified as moderately repetitive or as highly repetitive. The highly repetitive sequences consist of 5-500 base pair lengths repeated many times in tandem. These sequences are usually clustered in centromeres and telomeres of the chromosome and are present in about 1-10 milHon copies per haploid genome. These sequences are transcriptionally inactive and may play a strucmral role in the chromosome (see Chapter 40). 

The moderately repetitive sequences, which are defined as being present in numbers of less than 10 copies per haploid genome, are not clustered but are interspersed with unique sequences. In many cases, these long interspersed repeats are transcribed by RNA polymerase II and contain caps indistinguishable from those on mRNA. 

Rapid sequencing and single nucleotide polymorphisms (SNPs) will play a major role in associating sequence variations with heritable clinical phenotypes of drug or xenobiotic response. SNPs occur approximately once every 300-3,000 base pairs if one compares the genomes of two unrelated individuals [13, 14]. Any two individuals thus differ by approximately 1-10 million base pairs, i.e., in < 1% of the approximately 3.2 billion base pairs of the haploid genome (23 chromosomes). 

Table 14.1 Ranges of values of base pairs per haploid genome for selected groups of plants and animals ...

Taxonab Haploid genome size0 Picograms Megabases Reference... 

In mammals, some 10% of the DNA is highly repetitive, a further 20% is moderately reiterated and the remainder represents non-repetitive or single copy sequences. The rate of renaturation of DNA has been used to estimate that 16% of the DNA in H. diminuta is repetitive (746). Furthermore, the rate of reassociation of the single copy component in this species has allowed calculation of its haploid genome size, which is approximately... 

BCB domain-containing proteins are most abundant in plants, which are also the only organisms that contain genes encoding proteins of aU four classes. In the haploid genome of Arabidopsis thaliana, the complete... 

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