Related topics: genes · genome · cells · dna · cell division

Chromosomes look different than you think

In high school textbooks, human chromosomes are pictured as wonky Xs like two hotdogs jammed together. But those images are far from accurate. "For 90 percent of the time," said Jun-Han Su, "chromosomes don't exist like that."

The bull Y chromosome has evolved to bully its way into gametes

In a new study, published Nov. 18 in the journal Genome Research, scientists in the lab of Whitehead Institute Member David Page present the first ever full, high-resolution sequence of the Y chromosome of a Hereford bull. ...

A gel for dosage compensation

Human females have two X chromosomes, and males only one. This chromosome imbalance also extends to other branches of the animal kingdom. Interestingly, the humble fruit fly has devised a different way to 'equalize' these ...

Evolution of the Y chromosome in great apes deciphered

New analysis of the DNA sequence of the male-specific Y chromosomes from all living species of the great ape family helps to clarify our understanding of how this enigmatic chromosome evolved. A clearer picture of the evolution ...

The male Y chromosome does more than we thought

New light is being shed on a little-known role of Y chromosome genes, specific to males, that could explain why men suffer differently than women from various diseases, including COVID-19.

Neandertals have adopted male sex chromosome from modern humans

In 1997, the very first Neandertal DNA sequence—just a small part of the mitochondrial genome—was determined from an individual discovered in the Neander Valley, Germany, in 1856. Since then, improvements in molecular ...

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Chromosome

A chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions. The word chromosome comes from the Greek χρῶμα (chroma, color) and σῶμα (soma, body) due to their property of being very strongly stained by particular dyes. Chromosomes vary widely between different organisms. The DNA molecule may be circular or linear, and can be composed of 10,000 to 1,000,000,000 nucleotides in a long chain. Typically eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic cells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. Furthermore, cells may contain more than one type of chromosome; for example, mitochondria in most eukaryotes and chloroplasts in plants have their own small chromosomes.

In eukaryotes, nuclear chromosomes are packaged by proteins into a condensed structure called chromatin. This allows the very long DNA molecules to fit into the cell nucleus. The structure of chromosomes and chromatin varies through the cell cycle. Chromosomes are the essential unit for cellular division and must be replicated, divided, and passed successfully to their daughter cells so as to ensure the genetic diversity and survival of their progeny. Chromosomes may exist as either duplicated or unduplicated—unduplicated chromosomes are single linear strands, whereas duplicated chromosomes (copied during synthesis phase) contain two copies joined by a centromere. Compaction of the duplicated chromosomes during mitosis and meiosis results in the classic four-arm structure (pictured to the right). Chromosomal recombination plays a vital role in genetic diversity. If these structures are manipulated incorrectly, through processes known as chromosomal instability and translocation, the cell may undergo mitotic catastrophe and die, or it may aberrantly evade apoptosis leading to the progression of cancer.

However, in practice "chromosome" is a rather loosely defined term. In prokaryotes, a small circular DNA molecule may be called either a plasmid or a small chromosome. These small circular genomes are also found in mitochondria and chloroplasts, reflecting their bacterial origins. The simplest chromosomes are found in viruses: these DNA or RNA molecules are short linear or circular chromosomes that often lack any structural proteins.

This text uses material from Wikipedia, licensed under CC BY-SA