# Genetics guides

> Guides on DNA, genes, chromosomes, genome sequencing, and sequence file formats.

- [Oligo analyzer comparison](https://proteiniq.io/guides/oligo-analyzer-comparison): Oligo analyzers and primer Tm calculators disagree by several degrees on the same primer, mostly because they assume different salt, Mg2+ and oligo concentrations. We compare the methods, corrections, hairpin and dimer checks, outputs and access of IDT OligoAnalyzer, Primer3, NEB, Thermo Fisher, Promega and ProteinIQ.
- [How many chromosomes do different species have?](https://proteiniq.io/guides/chromosome-counts-by-species): Dogs have 78 chromosomes, cats 38, humans 46 and chimpanzees 48. See which other animals share our 46, which have the most and fewest, and why counts differ.
- [How long is human DNA?](https://proteiniq.io/guides/how-long-is-dna): Each human cell holds about 2 m of DNA, and the whole body about 14 billion km, or 96 times the distance from Earth to the Sun. Each base pair adds 0.34 nm.
- [How many genes do humans have?](https://proteiniq.io/guides/how-many-genes-do-humans-have): Humans have about 20,000 protein-coding genes: 19,442 in GENCODE v50, 19,878 in Ensembl 116 and 19,838 in CHESS 3.1.3. With RNA genes and pseudogenes, GENCODE lists 78,733.
- [How much DNA do humans share with other animals?](https://proteiniq.io/guides/human-animal-dna-similarity): Pigs do not share 98% of human DNA. Measured the same way for every species, a typical pig protein is 89% identical to the human one, against 99% for chimpanzees and 86% for rats.
- [How much DNA do humans share with bananas?](https://proteiniq.io/guides/human-banana-dna-similarity): Yes, but not 50%. About 18% of human genes have a banana counterpart, their proteins are about 40% identical, and only 0.08% of the human genome matches.
- [How big is the human genome?](https://proteiniq.io/guides/human-genome-size): The human genome is about 3.1 billion base pairs long per chromosome set, or 6.3 billion per cell. Compare GRCh38, T2T-CHM13 and genome file sizes in GB.
- [Introns vs exons: what is the difference?](https://proteiniq.io/guides/introns-vs-exons): Exons are the parts of a gene kept in mature RNA, while introns are removed by splicing. Learn how much of a human gene is intron, why exons are not the same as coding DNA, and what happens when splicing fails.
- [How much does it cost to sequence a genome?](https://proteiniq.io/guides/genome-sequencing-cost): A human genome costs about $220 to $450 at university sequencing labs and $399 to $595 as a consumer test. ProteinIQ's survey of US core facilities puts the median lab price at $419 before analysis.
- [How to make a FASTA file](https://proteiniq.io/guides/how-to-make-a-fasta-file): Create a FASTA file in Notepad or TextEdit, convert text, Word, or Excel data to FASTA, download FASTA from NCBI or UniProt, and avoid the mistakes that make tools reject the file.
- [How many genes are in mitochondrial DNA?](https://proteiniq.io/guides/how-many-genes-in-mitochondrial-dna): Human mitochondrial DNA has 37 canonical genes. Compare the standard count with evidence for additional small proteins and mtDNA copy numbers across tissues.
- [How accurate is DNA sequencing?](https://proteiniq.io/guides/dna-sequencing-accuracy): DNA sequencing accuracy ranges from about 99% per raw base to above 99.9% for high-quality or consensus reads. The exact figure depends on the platform, chemistry, software, sample, and metric.
- [How many genomes have been sequenced?](https://proteiniq.io/guides/genbank-statistics): NCBI indexes 3.67 million current public genome assemblies. See bacterial, plant, human, species, and GenBank sequence counts for 2026.
- [How many types of RNA are there?](https://proteiniq.io/guides/how-many-types-of-rna-are-there): There are three major RNA types: mRNA, rRNA, and tRNA. rRNA is the most abundant by mass, tRNA is the smallest of the three, and mRNA can be the longest.
- [How many transcripts are in the human transcriptome?](https://proteiniq.io/guides/human-transcriptome-size): The current human reference annotation contains 644,292 transcript models, 278,455 of them protein-coding. Database records, expressed isoforms and RNA molecules are different counts.
- [Which organisms have the largest and smallest genomes?](https://proteiniq.io/guides/largest-and-smallest-genomes): Compare 27 genome size records across animals, plants, fungi, protists, and bacteria, from a 160.45-billion-base-pair fern genome to a 50,141-base-pair bacterial symbiont genome.
- [What are the largest and smallest human genes?](https://proteiniq.io/guides/largest-and-smallest-human-genes): RBFOX1 is the largest human protein-coding gene by GENCODE v50 genomic span. MLDHR is the shortest under an HGNC-approved protein-coding filter, at 96 base pairs.
- [How many druggable genes are there?](https://proteiniq.io/guides/druggable-genome): About 4,500 human genes are considered part of the druggable genome. A major analysis counted 4,479 drugged or druggable genes, equal to 22% of protein-coding genes.
- [How long does PCR take?](https://proteiniq.io/guides/how-long-does-pcr-take): Most PCR runs take about 45 minutes to 2 hours in a thermocycler. Compare conventional PCR, qPCR, and RT-qPCR times and see how cycle count and target length affect the run.
- [How long does whole-genome sequencing take?](https://proteiniq.io/guides/human-genome-sequencing-time): Human whole-genome sequencing can generate genome data in hours to about a day. Sample preparation, analysis, interpretation, and reporting can extend the full turnaround to weeks.
- [How long does mRNA last in a cell?](https://proteiniq.io/guides/how-long-does-mrna-last-in-a-cell): Cellular mRNA has a half-life of a few minutes in bacteria, about 18 minutes in budding yeast, and several hours in cultured human cells.
- [How many nucleosomes are in a human cell?](https://proteiniq.io/guides/how-many-nucleosomes-are-in-a-human-cell): A typical diploid human cell contains about 30 million nucleosomes. See how that estimate is calculated and why a nucleosome can be described as containing 146, 166, or about 200 base pairs.
- [How many RNA polymerases do eukaryotes have?](https://proteiniq.io/guides/how-many-rna-polymerases-do-eukaryotes-have): Eukaryotes have three canonical nuclear RNA polymerases, while land plants have five. DNA polymerase counts vary by species, from five in E. coli to 16 in humans.
- [How much DNA is needed for sequencing?](https://proteiniq.io/guides/how-much-dna-is-needed-for-sequencing): Most DNA sequencing workflows start with 1 ng to 1 µg of DNA. Illumina DNA Prep recommends 100–500 ng for human DNA, while Nanopore ligation libraries use 1 µg for fragments longer than 10 kb.
- [How many chromosomes do humans have?](https://proteiniq.io/guides/how-many-chromosomes-do-humans-have): Humans typically have 46 chromosomes in most nucleated body cells: 44 autosomes and 2 sex chromosomes. Egg and sperm cells have 23 each.
- [How many codons are there?](https://proteiniq.io/guides/how-many-codons-are-there): There are 64 possible codons in the standard genetic code. Of these, 61 specify amino acids and three are stop codons.
- [How many CpG sites are in the human genome?](https://proteiniq.io/guides/how-many-cpg-sites-in-human-genome): The human genome contains about 28 million CpG sites. A 2023 whole-genome methylation atlas analyzed 28,217,448 CpG positions, or roughly one per 110 base pairs.
- [How many genes are in a chromosome?](https://proteiniq.io/guides/how-many-genes-are-in-a-chromosome): Human nuclear chromosomes contain between 61 and 2,016 protein-coding genes. See the current gene count for chromosomes 1 through 22, X, Y, and mitochondrial DNA.
- [How much DNA do cousins share?](https://proteiniq.io/guides/how-much-dna-do-cousins-share): First cousins share 12.5% of their autosomal DNA by descent on average, second cousins share 3.125%, and third cousins share 0.781%.
- [How much DNA do siblings share?](https://proteiniq.io/guides/how-much-dna-do-siblings-share): Full siblings share about 50% of their autosomal DNA by descent on average. Identical twins share virtually 100%, while half-siblings average 25%.
- [How long does DNA last?](https://proteiniq.io/guides/how-long-does-dna-last): DNA can remain detectable for days, years, or millennia. Its survival depends more on temperature, water, sunlight, microbes, and the sample material than on age alone.
- [How long does DNA replication take?](https://proteiniq.io/guides/how-long-does-dna-replication-take): Human DNA replication takes about 8 hours. See measured replication fork speeds, bacterial replication times, and how thousands of origins copy the genome in parallel.
- [How many ribosomes are in a cell?](https://proteiniq.io/guides/how-many-ribosomes-are-in-a-cell): Ribosome counts range from thousands in bacteria to millions in mammalian cells. Compare bacterial, yeast, and mammalian cells, translation speeds, protein output, and polysomes.
- [How many SNPs are in the human genome?](https://proteiniq.io/guides/how-many-snps-are-in-the-human-genome): A typical human genome has about 5 million single-nucleotide variants relative to a reference. About 10 million SNP sites are common across the population.
- [What percentage of the human genome is viral DNA?](https://proteiniq.io/guides/human-genome-viral-dna): About 8% of the human genome is viral DNA in the standard sense: inherited endogenous retrovirus sequences. That is about 250 million bases in a 3.1-billion-base reference genome.
- [How much DNA do humans share with chimpanzees?](https://proteiniq.io/guides/human-chimp-dna-similarity): Humans and chimpanzees share about 98.8% of directly comparable DNA sequence, or about 96% once insertions and deletions are counted in the classic 2005 comparison.
- [How much of the human genome is junk DNA?](https://proteiniq.io/guides/human-genome-junk-dna): Between 8% and 80% of the human genome may be functional, depending on how function is defined. By the stricter evolutionary definition, about 8 to 15% is under selective constraint.