Chromosome

chromosomeschromosomalChromosomal numberhuman chromosomebacterial chromosomechromosomally chromosome numberchromosomal DNAchromosomal pairsDNA packaging
A chromosome is a deoxyribonucleic acid (DNA) molecule with part or all of the genetic material (genome) of an organism.wikipedia
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Histone

histoneshistone modificationhistone modifications
Most eukaryotic chromosomes include packaging proteins which, aided by chaperone proteins, bind to and condense the DNA molecule to prevent it from becoming an unmanageable tangle.
Without histones, the unwound DNA in chromosomes would be very long (a length to width ratio of more than 10 million to 1 in human DNA).

Centromere

acrocentricsubmetacentriccentromeric
Before this happens, every chromosome is copied once (S phase), and the copy is joined to the original by a centromere, resulting either in an X-shaped structure (pictured here) if the centromere is located in the middle of the chromosome or a two-arm structure if the centromere is located near one of the ends.
The centromere is the specialized DNA sequence of a chromosome that links a pair of sister chromatids (a dyad).

Genome

genomesgenetic materialgenomic
A chromosome is a deoxyribonucleic acid (DNA) molecule with part or all of the genetic material (genome) of an organism.
The Oxford Dictionary suggests the name is a blend of the words gene and chromosome.

DNA

deoxyribonucleic aciddouble-stranded DNAdsDNA
A chromosome is a deoxyribonucleic acid (DNA) molecule with part or all of the genetic material (genome) of an organism.
Within eukaryotic cells, DNA is organized into long structures called chromosomes.

Sexual reproduction

sexuallysexualreproduce sexually
Chromosomal recombination during meiosis and subsequent sexual reproduction play a significant role in genetic diversity.
Sexual reproduction is a type of life cycle where generations alternate between cells with a single set of chromosomes (haploid) and cells with a double set of chromosomes (diploid).

Meiosis

meioticsyzygymeiosis I
Chromosomal recombination during meiosis and subsequent sexual reproduction play a significant role in genetic diversity. In the early stages of mitosis or meiosis (cell division), the chromatin double helix become more and more condensed.
Meiosis (from Greek μείωσις, meiosis, which means lessening) is a special type of cell division that reduces the chromosome number by half, creating four haploid cells, each genetically distinct from the parent cell that gave rise to them.

Cell division

divisiondaughter cellcellular division
Chromosomes are normally visible under a light microscope only when the cell is undergoing the metaphase of cell division (where all chromosomes are aligned in the center of the cell in their condensed form).
In eukaryotes, there are two distinct types of cell division: a vegetative division, whereby each daughter cell is genetically identical to the parent cell (mitosis), and a reproductive cell division, whereby the number of chromosomes in the daughter cells is reduced by half to produce haploid gametes (meiosis).

Metaphase

chromosomal misalignmentMM-phase
Chromosomes are normally visible under a light microscope only when the cell is undergoing the metaphase of cell division (where all chromosomes are aligned in the center of the cell in their condensed form).
These chromosomes, carrying genetic information, align in the equator of the cell before being separated into each of the two daughter cells.

Anaphase

In animal cells, chromosomes reach their highest compaction level in anaphase during chromosome segregation.
Anaphase (from the Greek ἀνά, "up" and φάσις, "stage"), is the stage of mitosis after the process of metaphase, when replicated chromosomes are split and the newly-copied chromosomes (daughter chromatids) are moved to opposite poles of the cell.

Heinrich Wilhelm Gottfried von Waldeyer-Hartz

Heinrich Wilhelm WaldeyerWilhelm von Waldeyer-HartzWilhelm Waldeyer
The term was coined by the German scientist von Waldeyer-Hartz, referring to the term chromatin, which was itself introduced by Walther Flemming, who discovered cell division.
Heinrich Wilhelm Gottfried von Waldeyer-Hartz (6 October 1836 – 23 January 1921) was a German anatomist, known for summarizing neuron theory and for naming the chromosome.

Chromatin

chromatin structuresex chromatinnuclear chromatin
The term was coined by the German scientist von Waldeyer-Hartz, referring to the term chromatin, which was itself introduced by Walther Flemming, who discovered cell division.
During mitosis and meiosis, chromatin facilitates proper segregation of the chromosomes in anaphase; the characteristic shapes of chromosomes visible during this stage are the result of DNA being coiled into highly condensed networks of chromatin.

Thomas Hunt Morgan

T. H. MorganThomas H. MorganT.H. Morgan
Ernst Mayr remarks that the theory was hotly contested by some famous geneticists: William Bateson, Wilhelm Johannsen, Richard Goldschmidt and T.H. Morgan, all of a rather dogmatic turn of mind.
Thomas Hunt Morgan (September 25, 1866 – December 4, 1945) was an American evolutionary biologist, geneticist, embryologist, and science author who won the Nobel Prize in Physiology or Medicine in 1933 for discoveries elucidating the role that the chromosome plays in heredity.

Sister chromatids

sister chromatidcopynon-sister chromatids
The original chromosome and the copy are now called sister chromatids.
A sister chromatid refers to the identical copies (chromatids) formed by the DNA replication of a chromosome, with both copies joined together by a common centromere.

Joe Hin Tjio

Joe Hin TijoTjio
His error was copied by others and it was not until 1956 that the true number, 46, was determined by Indonesia-born cytogeneticist Joe Hin Tjio.
He was renowned as the first person to recognize the normal number of human chromosomes.

Boveri–Sutton chromosome theory

Boveri-Sutton chromosome theorychromosomal inheritancechromosome theory of heredity
In his famous textbook The Cell in Development and Heredity, Wilson linked together the independent work of Boveri and Sutton (both around 1902) by naming the chromosome theory of inheritance the Boveri–Sutton chromosome theory (the names are sometimes reversed).
The Boveri–Sutton chromosome theory (also known as the chromosome theory of inheritance or the Sutton–Boveri theory) is a fundamental unifying theory of genetics which identifies chromosomes as the carriers of genetic material.

Walter Sutton

SuttonSutton, Walter Stanborough
Boveri influenced two generations of American cytologists: Edmund Beecher Wilson, Nettie Stevens, Walter Sutton and Theophilus Painter were all influenced by Boveri (Wilson, Stevens, and Painter actually worked with him).
Walter Stanborough Sutton (April 5, 1877 – November 10, 1916) was an American geneticist and physician whose most significant contribution to present-day biology was his theory that the Mendelian laws of inheritance could be applied to chromosomes at the cellular level of living organisms.

Extrachromosomal DNA

extrachromosomalCircular DNAextrachromosomal elements
Certain bacteria also contain plasmids or other extrachromosomal DNA.
Extrachromosomal DNA (abbreviated ecDNA) is any DNA that is found off the chromosomes, either inside or outside the nucleus of a cell.

Origin of replication

origins of replicationreplication originoriC
Bacteria typically have a one-point (the origin of replication) from which replication starts, whereas some archaea contain multiple replication origins.
Propagation of the genetic material between generations requires timely and accurate duplication of DNA by semiconservative replication prior to cell division to ensure each daughter cell receives the full complement of chromosomes.

Theodor Boveri

BoveriChromatin diminutionTheodor Heinrich Boveri
In a series of experiments beginning in the mid-1880s, Theodor Boveri gave the definitive demonstration that chromosomes are the vectors of heredity; his two principles or postulates were the continuity of chromosomes and the individuality of chromosomes.
Boveri's work with sea urchins showed that it was necessary to have all chromosomes present in order for proper embryonic development to take place.

DNA condensation

chromosome condensationcondensationcondense
Most eukaryotic chromosomes include packaging proteins which, aided by chaperone proteins, bind to and condense the DNA molecule to prevent it from becoming an unmanageable tangle.
Bacterial DNA is sometimes referred to as the bacterial chromosome.

Cancer

cancersmalignanciescancerous
Usually, this will make the cell initiate apoptosis leading to its own death, but sometimes mutations in the cell hamper this process and thus cause progression of cancer.
The gain or loss of an entire chromosome can occur through errors in mitosis.

Cell nucleus

nucleusnucleinuclear
Chromatin allows the very long DNA molecules to fit into the cell nucleus.
The cell nucleus contains all of the cell's genome, except for a small fraction of mitochondrial DNA, organized as multiple long linear DNA molecules in a complex with a large variety of proteins, such as histones, to form chromosomes.

Bacteria

bacteriumbacterialEubacteria
The prokaryotes – bacteria and archaea – typically have a single circular chromosome, but many variations exist.
The nucleoid contains the chromosome with its associated proteins and RNA.

Mitosis

mitoticmitosesmitotic division
In the early stages of mitosis or meiosis (cell division), the chromatin double helix become more and more condensed.
In cell biology, mitosis is a part of the cell cycle when replicated chromosomes are separated into two new nuclei.

Nucleosome

nucleosomesnucleosome core particlenuclesome
Chromatin fiber is made of nucleosomes (histone octamers with part of a DNA strand attached to and wrapped around it).
Nucleosomes are folded through a series of successively higher order structures to eventually form a chromosome; this both compacts DNA and creates an added layer of regulatory control, which ensures correct gene expression.