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Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid DNA. Passed from parents to offspring, DNA contains the specific instructions that make each type of living creature unique. The term chromosome comes from the Greek words for color chroma and body soma. Scientists gave this name to chromosomes because they are cell structures, or bodies, that are strongly stained by some colorful dyes used in research.

The unique structure of chromosomes keeps DNA tightly wrapped around spool-like proteins, called histones. Without such packaging, DNA molecules would be too long to fit inside cells. For example, if all of the DNA molecules in a single human cell were unwound from their histones and placed end-to-end, they would stretch 6 feet. For an organism to grow and function properly, cells must constantly divide to produce new cells to replace old, worn-out cells.

During cell division, it is essential that DNA remains intact and evenly distributed among cells. Chromosomes are a key part of the process that ensures DNA is accurately copied and distributed in the vast majority of cell divisions.

Still, mistakes do occur on rare occasions. Changes in the number or structure of chromosomes in new cells may lead to serious problems.

For example, in humans, one type of leukemia and some other cancers are caused by defective chromosomes made up of joined pieces of broken chromosomes.

It is also crucial that reproductive cells, such as eggs and sperm, contain the right number of chromosomes and that those chromosomes have the correct structure. If not, the resulting offspring may fail to develop properly. For example, people with Down syndrome have three copies of chromosome 21, instead of the two copies found in other people. Chromosomes vary in number and shape among living things. Most bacteria have one or two circular chromosomes.

Humans, along with other animals and plants, have linear chromosomes that are arranged in pairs within the nucleus of the cell. The only human cells that do not contain pairs of chromosomes are reproductive cells, or gametes, which carry just one copy of each chromosome. When two reproductive cells unite, they become a single cell that contains two copies of each chromosome. This cell then divides and its successors divide numerous times, eventually producing a mature individual with a full set of paired chromosomes in virtually all of its cells.

Besides the linear chromosomes found in the nucleus, the cells of humans and other complex organisms carry a much smaller type of chromosome similar to those seen in bacteria. This circular chromosome is found in mitochondria, which are structures located outside the nucleus that serve as the cell's powerhouses. Scientists think that, in the past, mitochondria were free-living bacteria with the ability to convert oxygen into energy.

When these bacteria invaded cells lacking the power to tap into oxygen's power, the cells retained them, and, over time, the bacteria evolved into modern-day mitochondria. The constricted region of linear chromosomes is known as the centromere. Although this constriction is called the centromere, it usually is not located exactly in the center of the chromosome and, in some cases, is located almost at the chromosome's end.

The regions on either side of the centromere are referred to as the chromosome's arms.Chromosomes are thread-like molecules that carry hereditary information for everything from height to eye color. They are made of protein and one molecule of DNA, which contains an organism's genetic instructions, passed down from parents. In humans, animals, and plants, most chromosomes are arranged in pairs within the nucleus of a cell. Humans have 22 of these chromosome pairs, called autosomes.

Humans have an additional pair of sex chromosomes for a total of 46 chromosomes. The sex chromosomes are referred to as X and Y, and their combination determines a person's sex. Typically, human females have two X chromosomes while males possess an XY pairing.

This XY sex-determination system is found in most mammals as well as some reptiles and plants. Whether a person has XX or XY chromosomes is determined when a sperm fertilizes an egg. Unlike the body's other cells, the cells in the egg and sperm — called gametes or sex cells — possess only one chromosome. Gametes are produced by meiosis cell division, which results in the divided cells having half the number of chromosomes as the parent, or progenitor, cells.

In the case of humans, this means that parent cells have two chromosomes and gametes have one. All of the gametes in the mother's eggs possess X chromosomes. The father's sperm contains about half X and half Y chromosomes.

The sperm are the variable factor in determining the sex of the baby. If the sperm carries an X chromosome, it will combine with the egg's X chromosome to form a female zygote. If the sperm carries a Y chromosomeit will result in a male. During fertilization, gametes from the sperm combine with gametes from the egg to form a zygote. The zygote contains two sets of 23 chromosomes, for the required There are some variations, though. Recent research has found that a person can have a variety of different combinations of sex chromosomes and genes, particularly those who identify as LGBT.

For example, a certain X chromosome called Xq28 and a gene on chromosome 8 seem to be found in higher prevalence in men who are gay, according to a study in the journal Psychological Medicine.

A few births out of a thousand of babies are born with a single sex chromosome 45X or 45Y and are referred to as sex monosomies.Genetics research studies how individual genes or groups of genes are involved in health and disease.

chromosomes

Understanding genetic factors and genetic disorders is important in learning more about promoting health and preventing disease. Some genetic changes have been associated with an increased risk of having a child with a birth defect or developmental disability or developing diseases like cancer or heart disease. Genetics also can help us understand how medical conditions happen. People get inherit their chromosomeswhich contain their genesfrom their parents.

Chromosomes come in pairs and humans have 46 chromosomes, in 23 pairs. Children randomly get one of each pair of chromosomes from their mother and one of each pair from their father. The chromosomes that form the 23rd pair are called the sex chromosomes. They decide if a person is male or female. A female has two X chromosomes, and a male has one X and one Y chromosome. Each daughter gets an X from her mother and an X from her father.

Each son gets an X from his mother and a Y from his father. Genetic disorders can happen for many reasons. Genetic disorders often are described in terms of the chromosome that contains the gene.

If the gene is on one of the first 22 pairs of chromosomes, called the autosomes, the genetic disorder is called an autosomal condition. If the gene is on the X chromosome, the disorder is called X-linked. Genetic disorders also are grouped by how they run in families.

Disorders can be dominant or recessive, depending on how they cause conditions and how they run in families. Dominant diseases can be caused by only one copy of a gene with a DNA mutation. For recessive diseases, both copies of a gene must have a DNA mutation in order to get one of these diseases.

In such cases, each parent is called a carrier of the disease. They can pass the disease on to their children, but do not have the disease themselves. For example, suppose part of a gene usually has the sequence TAC. A mutation can change the sequence to TTC in some people. Mutations can be passed down to a child from his or her parents. Or, they can happen for the first time in the sperm or egg, so that the child will have the mutation but the parents will not.

Single gene disorders can be autosomal or X-linked. It is caused by a mutation in a gene found on chromosome Sickle cell disease causes anemia and other complications. Fragile X syndromeon the other hand, is an X-linked single gene disorder. It is caused by a change in a gene on the X chromosome. It is the most common known cause of intellectual disability and developmental disability that can be inherited passed from one generation to the next.

People usually have 23 pairs of chromosomes. But, sometimes a person is born with a different number. If a person has an extra chromosome it is called trisomy.

If a person has a missing chromosome it is called monosomy. For example, people with Down syndrome have an extra copy of chromosome Some disorders are caused by having a different number of sex chromosomes.A chromosome is a DNA deoxyribonucleic acid molecule with part or all of the genetic material genome of an organism.

Most eukaryotic chromosomes include packaging proteins which, aided by chaperone proteinsbind to and condense the DNA molecule to prevent it from becoming an unmanageable tangle. 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.

The original chromosome and the copy are now called sister chromatids. During metaphase the X-shape structure is called a metaphase chromosome. In this highly condensed form chromosomes are easiest to distinguish and study. Chromosomal recombination during meiosis and subsequent sexual reproduction play a significant role in genetic diversity.

If these structures are manipulated incorrectly, through processes known as chromosomal instability and translocation, the cell may undergo mitotic catastrophe. 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.

Some use the term chromosome in a wider sense, to refer to the individualized portions of chromatin in cells, either visible or not under light microscopy. Others use the concept in a narrower sense, to refer to the individualized portions of chromatin during cell division, visible under light microscopy due to high condensation.

Some of the early karyological terms have become outdated. In a series of experiments beginning in the mids, 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.

Genetics - Chromosome Structure and Types - Lesson 18

Aided by the rediscovery at the start of the s of Gregor Mendel 's earlier work, Boveri was able to point out the connection between the rules of inheritance and the behaviour of the chromosomes. In his famous textbook The Cell in Development and HeredityWilson linked together the independent work of Boveri and Sutton both around by naming the chromosome theory of inheritance the Boveri—Sutton chromosome theory the names are sometimes reversed.

Morganall of a rather dogmatic turn of mind. Eventually, complete proof came from chromosome maps in Morgan's own lab. The number of human chromosomes was published in by Theophilus Painter.

By inspection through the microscope, he counted 24 pairs, which would mean 48 chromosomes. His error was copied by others and it was not until that the true number, 46, was determined by Indonesia-born cytogeneticist Joe Hin Tjio. Prokaryotic chromosomes have less sequence-based structure than eukaryotes.

Bacteria typically have a one-point the origin of replication from which replication starts, whereas some archaea contain multiple replication origins. Prokaryotes do not possess nuclei. Instead, their DNA is organized into a structure called the nucleoid.

This structure is, however, dynamic and is maintained and remodeled by the actions of a range of histone-like proteins, which associate with the bacterial chromosome.

Certain bacteria also contain plasmids or other extrachromosomal DNA. These are circular structures in the cytoplasm that contain cellular DNA and play a role in horizontal gene transfer. Bacterial chromosomes tend to be tethered to the plasma membrane of the bacteria. In molecular biology application, this allows for its isolation from plasmid DNA by centrifugation of lysed bacteria and pelleting of the membranes and the attached DNA.

Prokaryotic chromosomes and plasmids are, like eukaryotic DNA, generally supercoiled. The DNA must first be released into its relaxed state for access for transcriptionregulation, and replication.Chromosomethe microscopic threadlike part of the cell that carries hereditary information in the form of genes. A defining feature of any chromosome is its compactness. The structure and location of chromosomes are among the chief differences between viruses, prokaryotesand eukaryotes.

The nonliving viruses have chromosomes consisting of either DNA deoxyribonucleic acid or RNA ribonucleic acid ; this material is very tightly packed into the viral head. Among organisms with prokaryotic cells i. The single chromosome of a prokaryotic cell is not enclosed within a nuclear membrane.

Among eukaryotes, the chromosomes are contained in a membrane-bound cell nucleus. The chromosomes of a eukaryotic cell consist primarily of DNA attached to a protein core. They also contain RNA. The remainder of this article pertains to eukaryotic chromosomes. Every eukaryotic species has a characteristic number of chromosomes chromosome number.

In species that reproduce asexually, the chromosome number is the same in all the cells of the organism. Among sexually reproducing organisms, the number of chromosomes in the body somatic cells is diploid 2 n ; a pair of each chromosometwice the haploid 1 n number found in the sex cells, or gametes. The haploid number is produced during meiosis. During fertilizationtwo gametes combine to produce a zygotea single cell with a diploid set of chromosomes. See also polyploidy.

Somatic cells reproduce by dividing, a process called mitosis. Between cell divisions the chromosomes exist in an uncoiled state, producing a diffuse mass of genetic material known as chromatin.

The uncoiling of chromosomes enables DNA synthesis to begin. During this phase, DNA duplicates itself in preparation for cell division. Following replication, the DNA condenses into chromosomes. At this point, each chromosome actually consists of a set of duplicate chromatids that are held together by the centromere. The centromere is the point of attachment of the kinetochore, a protein structure that is connected to the spindle fibres part of a structure that pulls the chromatids to opposite ends of the cell.

During the middle stage in cell division, the centromere duplicates, and the chromatid pair separates; each chromatid becomes a separate chromosome at this point. The cell divides, and both of the daughter cells have a complete diploid set of chromosomes. The chromosomes uncoil in the new cells, again forming the diffuse network of chromatin.

Among many organisms that have separate sexes, there are two basic types of chromosomes: sex chromosomes and autosomes. Autosomes control the inheritance of all the characteristics except the sex-linked ones, which are controlled by the sex chromosomes. Humans have 22 pairs of autosomes and one pair of sex chromosomes.

All act in the same way during cell division. For information on sex-linked characteristics, see linkage group. Chromosome breakage is the physical breakage of subunits of a chromosome.A chromosome is a DNA deoxyribonucleic acid molecule with part or all of the genetic material genome of an organism. Most eukaryotic chromosomes include packaging proteins which, aided by chaperone proteinsbind to and condense the DNA molecule to prevent it from becoming an unmanageable tangle.

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.

The original chromosome and the copy are now called sister chromatids. During metaphase the X-shape structure is called a metaphase chromosome.

In this highly condensed form chromosomes are easiest to distinguish and study. Chromosomal recombination during meiosis and subsequent sexual reproduction play a significant role in genetic diversity. If these structures are manipulated incorrectly, through processes known as chromosomal instability and translocation, the cell may undergo mitotic catastrophe. 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.

chromosome

Some use the term chromosome in a wider sense, to refer to the individualized portions of chromatin in cells, either visible or not under light microscopy. Others use the concept in a narrower sense, to refer to the individualized portions of chromatin during cell division, visible under light microscopy due to high condensation. Some of the early karyological terms have become outdated. In a series of experiments beginning in the mids, 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.

Aided by the rediscovery at the start of the s of Gregor Mendel 's earlier work, Boveri was able to point out the connection between the rules of inheritance and the behaviour of the chromosomes. In his famous textbook The Cell in Development and HeredityWilson linked together the independent work of Boveri and Sutton both around by naming the chromosome theory of inheritance the Boveri—Sutton chromosome theory the names are sometimes reversed.

Morganall of a rather dogmatic turn of mind. Eventually, complete proof came from chromosome maps in Morgan's own lab. The number of human chromosomes was published in by Theophilus Painter.

By inspection through the microscope, he counted 24 pairs, which would mean 48 chromosomes. His error was copied by others and it was not until that the true number, 46, was determined by Indonesia-born cytogeneticist Joe Hin Tjio. Prokaryotic chromosomes have less sequence-based structure than eukaryotes. Bacteria typically have a one-point the origin of replication from which replication starts, whereas some archaea contain multiple replication origins.

Prokaryotes do not possess nuclei. Instead, their DNA is organized into a structure called the nucleoid.To save this word, you'll need to log in.

chromosomes

This Test Could Change That. Armadillo quads offer an answer," 20 Dec. Send us feedback. The name 'primary loops' is not suitable, since it is by no means the case that these things always have the form of a loop. On the other hand, they are so important that a special shorter name seems desirable.

Plattner uses the expression 'karyosomes,' but as this too readily brings to mind nucleoli, another name is to be preferred. If the name I propose is serviceable, it will become customary, otherwise it will soon pass into oblivion. See more words from the same year Dictionary Entries near chromosome chromoprotein chromoscope chromosomal vesicle chromosome chromosome number chromosome set chromosomin.

Genetics Basics

Accessed 18 Apr. Keep scrolling for more More Definitions for chromosome chromosome. Please tell us where you read or heard it including the quote, if possible.

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chromosomes

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