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The human genome has many different regulatory sequences which are crucial to controlling gene expression. Conservative estimates indicate that these sequences make up 8% of the genome, [27] however extrapolations from the ENCODE project give that 20 [28] or more [29] of the genome is gene regulatory sequence.
In 2015, the 1000 Genomes Project, which sequenced one thousand individuals from 26 human populations, found that "a typical [individual] genome differs from the reference human genome at 4.1 million to 5.0 million sites … affecting 20 million bases of sequence"; the latter figure corresponds to 0.6% of total number of base pairs. [2]
Popular definitions of 'allele' typically refer only to different alleles within genes. For example, the ABO blood grouping is controlled by the ABO gene, which has six common alleles (variants). In population genetics, nearly every living human's phenotype for the ABO gene is some combination of just these six alleles. [5] [6]
In diploid organisms (like humans), the somatic cells possess two copies of the genome, one inherited from the male and one from the female. Each autosomal gene is therefore represented by two copies, or alleles, with one copy inherited from each parent at fertilization. The expressed allele is dependent upon its parental origin. For example ...
The human genome is believed to contain around 20,000–25,000 genes. In addition to studying chromosomes to the level of individual genes, genetic testing in a broader sense includes biochemical tests for the possible presence of genetic diseases , or mutant forms of genes associated with increased risk of developing genetic disorders.
In genetics, a locus (pl.: loci) is a specific, fixed position on a chromosome where a particular gene or genetic marker is located. [1] Each chromosome carries many genes, with each gene occupying a different position or locus; in humans, the total number of protein-coding genes in a complete haploid set of 23 chromosomes is estimated at ...
Gene conversion is the process by which one DNA sequence replaces a homologous sequence such that the sequences become identical after the conversion. [1] Gene conversion can be either allelic, meaning that one allele of the same gene replaces another allele, or ectopic, meaning that one paralogous DNA sequence converts another.
The human genome is the total collection of genes in a human being contained in the human chromosome, composed of over three billion nucleotides. [2] In April 2003, the Human Genome Project was able to sequence all the DNA in the human genome, and to discover that the human genome was composed of around 20,000 protein coding genes.