Sex chromosomes definition in science terms

Sex chromosomeeither of a pair of chromosomes that determine whether an individual is male or female. The sex chromosomes of human beings and other mammals are designated by scientists as X and Y.

In humans the sex chromosomes consist of one pair of the total of 23 pairs of chromosomes. The other 22 pairs of chromosomes are called autosomes. The X chromosome resembles a large autosomal chromosome with a long and a short arm. The Y chromosome has one long arm and a very short second arm. This path to maleness or femaleness originates at the moment of meiosiswhen a cell divides to produce gametesor sex cells having half the normal number of chromosomes.

During meiosis the male XY sex-chromosome pair separates and passes on an X or a Y to separate gametes; the result is that one-half of the gametes sperm that are formed contains the X chromosome and the other half contains the Y chromosome.

The female has two X chromosomes, and all female egg cells normally carry a single X. The eggs fertilized by X-bearing sperm become females XXwhereas those fertilized by Y-bearing sperm become males XY.

sex chromosomes definition in science terms

Unlike the paired autosomes, in which each member normally carries alleles forms of the same genes, the paired sex chromosomes do not carry an identical complement of genetic information.

The X chromosome, being larger, carries many more genes than does the Y. Traits controlled by genes found only on the X chromosome are said to be sex-linked see linkage group.

Recessive sex-linked traits, such as hemophilia and red—green colour blindnessoccur far more frequently in men than in women. This is because the male who inherits the recessive allele on his X chromosome has no allele on his Y chromosome to counteract its effects.

The female, on the other hand, must inherit the recessive allele on both of her X chromosomes in order to fully display the trait.

A woman who inherits the recessive allele for a sex-linked disorder on one of her X chromosomes may, however, show a limited expression of the trait.

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The reason for this is that, in each somatic cell of a normal female, one of the X chromosomes is randomly deactivated. This deactivated X chromosome can be seen as a small, dark-staining structure—the Barr body —in the cell nucleus.

The effects of genes carried only on the Y chromosome are, of course, expressed only in males.

sex chromosomes definition in science terms

Most of these genes are the so-called maleness determiners, which are necessary for development of the testes in the fetus. Several disorders are known to be associated with abnormal numbers of sex chromosomes.

See also X trisomy ; XYY-trisomy. Sex chromosome Article Media Additional Info. Print Cite verified Cite. While every effort has been made to follow citation style rules, there may be some discrepancies.

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A video about sex chromosomes and the inheritance of biological sex.

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Read More on This Topic.Homologous chromosomes are a pair of DNA molecules which contain information for the same genes, though each homologous chromosome may carry different alleles. A diploid organism like a human carries two copies of each gene, one on each part of this pair of homologous chromosomes.

Homologous chromosomes provide a number of functions to organisms, mainly in providing genetic variety. Homologous chromosomes typically have the same structure, because they contain genes coding for the same protein products.

While the alleles for the genes may differ slightly by a few nucleotidesthey are typically around the same length and form the same shape when condensed into a chromosome. Homologous chromosomes have the same function as any chromosome, they contain codons which specify the sequence of amino acids within a protein.

Each codon consists of a three-nucleotide sequence, which can be matched to an amino acid. To create large and complex proteins, genes must contain many thousands of nucleotides. Each protein then has a unique and specific function, which contributes to the actions of the entire cell.

Diploid organisms carry two copies of each gene for every protein they create. This allows for a number of different possibilities depending on the function of the protein. Some alleles create normally functioning proteins, some create non-functioning proteins, and others produce novel or more efficient proteins. With homologous chromosomes, two versions of each protein are created.

Homologous Chromosomes

This means that an organism can have many levels of protein functionality, from totally non-functional to hyper-functional. In combination with the many thousands of proteins an organism uses and the environment, this creates enormous variety in animals with homologous chromosomes.

Further, homologous chromosomes may engage in the process of homologous recombination during the process of meiosis. This random process swaps two parts of a pair of homologous chromosomes which contain the same genes.

This process adds even more variety, as it recombines the arrangement of genes you received from your parents. Below is a picture of a karyotypewhich is a graphic of sorted images showing every chromosome within a cell. Like the one below, most karyotypes show the homologous chromosomes next to each other.

Realistically, unless they are lined up during cell division, these homologous chromosomes are randomly distributed throughout the nucleus. If you look at the image above, you will see 22 pairs of homologous chromosomes as well as the sex chromosomes X and Y. If you look at any one of the pairs, you will notice the homologous chromosomes are always the same basic length and size. Look closer and you will notice that the dark banding on the homologous chromosomes seems to match.

This is because the chromosomes have the same basic structure, changing only at a few nucleotides. When the dark dye binds to the chromosome it prefers certain locations based on the molecular structure. Each of the homologous chromosomes is the same, so the dye stains them the same.

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Homologous chromosomes can only be identified this way when they are condensed. As chromatinthe individual molecules unwind into a loose structure that cannot be separated. Though some of the homologous chromosomes look like slightly different shapes in the above karyotype, they were likely being bent and pushed around by the cell membrane or other cellular components.

Homologous chromosomes are often confused with the similar term, sister chromatids. Sister chromatids are formed when DNA is copied. DNA is made of two complimentary strandswhich wrap around each other in a helix formation. As proteins replicate the DNA they split the strands apart, and match new nucleotides to each side.

The new strands grow, until two newly formed strands of DNA are completed.The two chromosomes in each body cell of a living thing that determine what sex it is. However much we gossip about heterosexual couples with large age gaps, we at least refrain from calling them sex offenders.

Scruff believes that sex is not the primary concern of users. To those who agreed with him, Bush pledged that the law against same-sex marriage would remain intact.

Bush busy engaging constituents on both sides of the same-sex marriage debate ahead of the presidential election. This week, Florida became the 36th state to allow same-sex marriage. Are you quite sure you have never suffered from this rather common disorder, gentle reader, at least, if you be of the male sex? But if you restrict it, to the sense in which it is commonly applied to the angelic sex, I am not prepared to answer.

As public accuser, he caused the death of immense numbers, of all ages and either sex. That he might lose his head and 'introduce an element of sex' was conscience confessing that it had been already introduced. He respected her courage and obvious power to rise above the personal attitude of her sex. Can you guess what they mean? The mother supplies only an X-chromosome, but the father can transmit both the X- and the Y-chromosome.

At fertilizationif the father's sperm is also carrying an X-chromosome, the child will be female. If the father's sperm is carrying a Y-chromosome, the child will be male. Words nearby sex chromosomes sexcentenarysex changesex chromatinsex chromosomesex chromosome imbalancesex chromosomessex crimesexdecillionsex determinationsexductionsexed. All rights reserved.

Words related to sex chromosomes heterochromosomesex chromatin. Example sentences from the Web for sex chromosomes However much we gossip about heterosexual couples with large age gaps, we at least refrain from calling them sex offenders. The Pastor's Fire-side Vol. The Wave Algernon Blackwood. Ancestors Gertrude Atherton.

List of Glossary of Zoology Terms and Definition

Get Help Now!Either of a pair of chromosomes in diploid cells, or a single chromosome in haploid cells, carrying genes that determine the sex and sex-linked characteristics of an organism. Most mammals, including humans, have one pair of sex chromosomes in diploid cells, designated XX in females and XY in males. Published by Houghton Mifflin Company.

All rights reserved. Collins Dictionary of Biology, 3rd ed. Hale, V. Saunders, J. Margham One of the thread-like structures located within the cell nucleus composed of an extremely long, double-stranded DNA deoxyribonucleic acid helix tightly folded around proteins called histones.

Each chromosome carries genes that contain the hereditary material that controls the growth and characteristics of the body. There are 46 chromosomes in each human somatic cell organized in 23 pairs, of which 22 pairs are similar in appearance but differ at the molecular level. They are called autosomal chromosomes or autosomes and are designated by a number with chromosome 1 being the longest, followed by chromosome 2, etc. The other pair, the sex chromosomes determines the sex of the individual.

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In mammals the two sex chromosomes of females are alike homologous and are referred to as X chromosomes. Males carry one X chromosome along with a much shorter chromosome, the Y chromosome. Each chromosome has a centromere that divides it into two arms, the short arm 'p' and the long arm 'q'.

Disorders of chromosome number in which the number of chromosomes is above or below the normal 46 are called aneuploidy. Common forms of aneuploidy are trisomy in which there is one extra chromosome and monosomy in which there is one less, than the normal They rarely cause specific eye diseases but affected individuals present ocular manifestations.

Examples : Down's syndrome trisomy of chromosome 21Edwards' syndrome trisomy 18Turner's syndrome monosomy 45 XO. There are other chromosome abnormalities such as translocation one segment of a chromosome is transferred to another chromosome as may occur in congenital anterior polar cataract, deletion a loss of a piece of chromosome as in aniridia, choroideremia, retinoblastoma, etc.

Other cases involve damage of a chromosome e. Millodot: Dictionary of Optometry and Visual Science, 7th edition. Mentioned in? References in periodicals archive? Frequencies of the various sex chromosome types at the St. Incipient speciation and additional diversity within the Simulium arcticum complex of black flies Diptera: Simuliidae. A syntenic region conserved from fish to mammalian X chromosome.

The science and management of sex verification in sport. In males, only autosomes were recognized, whereas sex chromosomes had a diffused structure Fig. The standard way of making reference to an individual's karyotype is to note the total number of chromosomes followed by the type of sex chromosomes. For example, normal human males have the 46, XY karyotype, whereas normal human females have the 46, XX karyotype.

Chapter 4: Sexual differentiation. Although White's interests covered many aspects of chromosome biology, he made relevant contributions to sex chromosome mechanisms and the evolution of sex chromosomes White a, b; a,b. Sex and neo-sex chromosomes in Orthoptera: a review.Biology is branch of Science in which living beings are studied. Biology has two main branches- 1. Botany -Study of different aspects of plants.

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Theophrastus is known as father of Botany. Zoology — Study of Various aspects of animals. Aristotle is called father of Zoology as well as Biology.

Here list of Glossary of Zoology Terms and Definition. View all articles by VidyaGyaan. Your email address will not be published. Notify me of follow-up comments by email. Notify me of new posts by email. State wise List of International Airports in India. Units of Physical Quantity. You Might Also Like Science. Leave a Reply Cancel reply Your email address will not be published. Search the site. It is a The fourth or digestive stomach of a ruminant, which leads from the third stomach omasum.

See ruminantia. It is a condition in which the normal skin colour is absent. It is caused by reduction or total lack of the pigment Melanin. It is a tube in multicellular animals through which food is taken into the body, digested and absorbed by the cells.

sex chromosomes definition in science terms

It is the class of back-boned land-animals like frogs, toads, newts and salamander. They are the first vertebrates that colonized land and can stay in water as well as on land. It is the study of human species in all its aspects including evolution, culture and population dynamics. It is a group of specific Proteins produced by mammals to defend themselves from foreign organisms or chemicals.

It is a foreign substance, usually proteins in nature, which elicits the formation of specific antibodies within an organism. It is a secretion the liver in animals. It is an alkaline fluid that helps in digestion and absorption of fats. It is the pressure exerted by blood on the walls of blood vessels, especially the main arteries. It is due to the pumping action of the heart.

Sex chromosome

The smallest tubes or vessels which form the connecting link between the circulatory and lymphatic system. Usually the walls are single layer thick. It is a group of organic compounds like sugars, starches and cellulose composed entirely of Carbon, Hydrogen and Oxygen.

They form the main source of energy for the human body. It is a mode of living by which animals and plants survive by eating the flesh of other animals.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.

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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.

Chromosome and Gene Terms

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.However much we gossip about heterosexual couples with large age gaps, we at least refrain from calling them sex offenders.

Scruff believes that sex is not the primary concern of users. To those who agreed with him, Bush pledged that the law against same-sex marriage would remain intact. Bush busy engaging constituents on both sides of the same-sex marriage debate ahead of the presidential election. This week, Florida became the 36th state to allow same-sex marriage. Are you quite sure you have never suffered from this rather common disorder, gentle reader, at least, if you be of the male sex?

But if you restrict it, to the sense in which it is commonly applied to the angelic sex, I am not prepared to answer. As public accuser, he caused the death of immense numbers, of all ages and either sex. That he might lose his head and 'introduce an element of sex' was conscience confessing that it had been already introduced.

He respected her courage and obvious power to rise above the personal attitude of her sex. See synonyms for sex chromosome on Thesaurus. Can you guess what they mean? Origin of sex chromosome First recorded in — Words nearby sex chromosome sex cellsex cellssexcentenarysex changesex chromatinsex chromosomesex chromosome imbalancesex chromosomessex crimesexdecillionsex determination. Words related to sex chromosome heterochromosomesex chromatin.

Example sentences from the Web for sex chromosome However much we gossip about heterosexual couples with large age gaps, we at least refrain from calling them sex offenders. The Pastor's Fire-side Vol. The Wave Algernon Blackwood. Ancestors Gertrude Atherton. Either of a pair of chromosomes, usually designated X or Y, that combine to determine the sex and sex-linked characteristics of an individual, with XX resulting in a female and XY in a male.


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