Kromosomi 18

Ihmisellä on 46 kromosomia joka solusa tavallisewsti ja ne ovat 23 parina.  kromosomia 18 on  kahtena kopiona,yksi kummaltakin vanhemmalta. kromosomissa 18 on 78 miljoonaa DNA-rakennusosasta, emäsparia ja se edustaa 2.5 %:a solun kokonaisDNA:sta. Geenitieteessä ollaan aktiivisti tunnistamassa  kromosomin jokaista geeniä. lukumäärä vaihtelee , koska tiedemiehet käyttävät määrittelyssä eri menetelmioä.  Todennäköistä on , että kromosomi 18 sisältää 200-300 geeniä, jotka  koodaavat proteiineja.  Näillä proteiineilla on erilaisia  osatehtäviään kehossa.

Lähde:  https://ghr.nlm.nih.gov/chromosome/18

• Humans normally have 46 chromosomes in each cell, divided into 23 pairs. Two copies of chromosome 18, one copy inherited from each parent, form one of the pairs. Chromosome 18 spans about 78 million DNA building blocks (base pairs) and represents approximately 2.5 percent of the total DNA in cells.

Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Chromosome 18 likely contains 200 to 300 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.

Geneetikot käyttävät idiogrammia  kromosomien standardikuvaamiseen. idiogrammi osoittaa kromosomin suhteellisen koon ja nauhamaisen rakenteen tummia ja vaaleita juovia, joita havaitaan kun kromosomit värjätään kemiallisin liuoksin ja siten tarkastellaan mikroskoopilla. Näitä juovia  käytetään kuvaamaan joka kromosomin geenien sijainteja ja ne ovat numeroituja. 

• Geneticists use diagrams called idiograms as a standard representation for chromosomes. Idiograms show a chromosome's relative size and its banding pattern, which is the characteristic pattern of dark and light bands that appears when a chromosome is stained with a chemical solution and then viewed under a microscope. These bands are used to describe the location of genes on each chromosome.

Credit: Genome Decoration Page/NCBI

Related Information

• How do geneticists indicate the location of a gene?

 https://www.ncbi.nlm.nih.gov/pubmed/16177791

 Chromosome 18 appears to have the lowest gene density of any human chromosome and is one of only three chromosomes for which trisomic individuals survive to term. There are also a number of genetic disorders stemming from chromosome 18 trisomy and aneuploidy. Here we report the finished sequence and gene annotation of human chromosome 18, which will allow a better understanding of the normal and disease biology of this chromosome. Despite the low density of protein-coding genes on chromosome 18, we find that the proportion of non-protein-coding sequences evolutionarily conserved among mammals is close to the genome-wide average. Extending this analysis to the entire human genome, we find that the density of conserved non-protein-coding sequences is largely uncorrelated with gene density. This has important implications for the nature and roles of non-protein-coding sequence elements.