What is the human genome?
What is the human genome?
The human genome, also known as the human genome, refers to the human genome, which consists of 23 pairs of chromosomes, including 22 pairs of autosomes and 1 pair of sex chromosomes. The human genome contains about 3.16 billion DNA base pairs, which are two nitrogenous bases joined by hydrogen bonds, starting with thymine (T), adenine (A), cytosine (C) and guanine. (G) The four bases are arranged into a base sequence, in which A and T are connected by two hydrogen bonds, and G and C are connected by three hydrogen bonds. The arrangement of base pairs in DNA can only be A to T, G to C. Some of these base pairs make up about 20,000 to 25,000 genes.
In the Human Genome Project, the biological and medical communities around the world investigated the sequence of eukaryotic genes in the human genome and found that the number of human genes is much smaller than originally expected. The coding sequence only accounts for about 1.5% of the total length.
Major Components of the Human Genome: Chromosomes and Genes
Chromosome:
The human genome is composed of 23 pairs of chromosomes (46 in total). Each chromosome contains hundreds of genes. Between genes, there is an intergenic segment that may contain regulatory sequences and non-coding DNA. Humans have 24 different chromosomes, of which 22 belong to the somatic chromosome, and there are two sex chromosomes that determine sex, the X chromosome and the Y chromosome. Chromosomes 1 to 22 are numbered roughly in order of their size from large to small. The largest chromosomes contain about 250 million base pairs, and the smallest about 38 million base pairs. These chromosomes are usually stored in the nucleus as filaments, and if the chromosomes in a single cell are drawn in a straight line, they will be about 6 feet long (1 foot = 30.48 cm).
The somatic cells of a human individual usually contain 1 to 22 pairs of somatic chromosomes from the parent, plus the X chromosome from the mother, and the X or Y chromosome from the father, for a total of 46 (23 pairs) chromosomes. Scientists divide these chromosomes into 7 groups: 1 to 3 are group A; 4 and 5 are group B; X chromosomes and 6-12 are group C; 13-15 is group D; 16 is To 18 is the E group; 19 and 20 are the F group; 21, 22 and Y chromosomes are the G group. For the average human, there are only two sets of chromosomes in each nucleus.
Gene:
There are an estimated 20,000 to 25,000 protein-coding genes in the human body. Originally, the estimated number was more than 100,000, but it was gradually revised down to the current number after better genome sequence quality and gene identification technology emerged. Although humans have fewer genes than some more primitive organisms, a large amount of alternative splicing (also translated as "alternative splicing") is used in human cells to insert introns into transcripts. The exons in the gene are selectively spliced and retained to form different RNA splicing products), which enables a gene to make a variety of different proteins, and the scale of the human proteome is also larger than the previous two. Species are bigger. That is to say, long-term evolution has made the coding efficiency of genes higher.
In addition to protein-coding genes, the human genome contains thousands of RNA genes (made up of RNA), including those used to transcribe transfer RNA (tRNA), ribosomal RNA (rRNA), and messenger RNA (mRNA). The gene in which rRNA is transcribed, called rDNA, is distributed on many different chromosomes.
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