Y chromosome


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chromosome

 [kro´mo-sōm]
in animal cells, a structure in the nucleus, containing a linear thread of deoxyribonucleic acid (DNA), which transmits genetic information and is associated with ribonucleic acid and histones. In bacterial genetics, a closed circle of double-stranded DNA that contains the genetic material of the cell and is attached to the cell membrane; the bulk of this material forms a compact bacterial nucleus. adj., adj chromoso´mal.

During cell division the material composing the chromosome is compactly coiled, making it visible with appropriate staining and permitting its movement in the cell with minimal entanglement. Each organism of a species is normally characterized by the same number of chromosomes in its somatic cells, 46 being the number normally present in humans, including 22 pairs of autosomes and the two sex chromosomes (XX or XY), which determine the sex of the organism. (See also heredity.)
Chromosome Analysis. This can be done on fetal cells obtained by amniocentesis or chorionic villus sampling, on lymphocytes from a blood sample, on skin cells from a biopsy, or on cells from products of conception such as an aborted fetus. The cells are then cultured in the laboratory until they divide. Cell division is arrested in mid-metaphase by the drug Colcemid. The chromosomes can be stained by one of several techniques that produce a distinct pattern of light and dark bands along the chromosomes, and each chromosome can be recognized by its size and banding pattern. The chromosomal characteristics of an individual are referred to as the karyotype. It is also possible to make a photomicrograph of a cell nucleus, cut it apart, and rearrange it so that the individual chromosomes are in order and labeled. The autosomes are numbered 1–22, roughly in order of decreasing length. The sex chromosomes are labeled X and Y. Karyotyping is useful in determining the presence of chromosome defects.

Before the chromosomes could be precisely identified they were placed in seven groups: A (chromosomes 1–3), B (4–5), C (6–12 and X), D (13–15), E (16–18), F (19–20), and G (21–22 and Y).
Chromosomal Abnormalities. The prevalence of chromosomal disorders cannot be fully and accurately determined because many of these disorders do not permit full embryonic and fetal development and therefore end in spontaneous abortion. About one in every 100 newborn infants do, however, have a gross demonstrable chromosomal abnormality. A large majority of cytogenetic abnormalities can be identified by cytogenetic analysis either before birth, by means of chorionic villus sampling or amniocentesis, or after birth.

Cytogenetic disorders with visible chromosomal abnormalities are evidenced by either an abnormal number of chromosomes or some alteration in the structure of one or more chromosomes. In the language of the geneticist, trisomy refers to the presence of an additional chromosome that is homologous with one of the existing pairs so that that particular chromosome is present in triplicate. An example of this type of disorder is a form of down syndrome (trisomy 21). Another example is patau's syndrome (trisomy 13), which produces severe anatomical malformations and profound mental retardation.

The term monosomy refers to the absence of one of a pair of homologous chromosomes. Monosomy involving an autosome usually results in the loss of too much genetic information to permit sufficient fetal development for a live birth. Either trisomy or monosomy involving the sex chromosomes yields relatively mild abnormalities.

A condition known as mosaicism results from an error in the distribution of chromosomes between daughter cells during an early embryonic cell division, producing two and sometimes three populations of cells with different chromosome numbers in the same individual. Mosaicism involving the sex chromosomes is not uncommon.

Other abnormal structural changes in the chromosome are consequences of some kind of chromosomal breakage, with either the loss or rearrangement of genetic material. translocation involves the transfer of a segment of one chromosome to another. inversion refers to a change in the sequence of genes along the chromosome, which occurs when there are two breaks in a chromosome and the segment between the breaks is reversed and reattached to the wrong ends. deletion occurs when a portion of a chromosome is lost. An example of this type of chromosomal abnormality is cri du chat syndrome, a deletion in the short arm of chromosome 5, marked by mental retardation and sometimes congenital heart defects. When deletion occurs at both ends of the chromosome, the two damaged ends can unite to form a circle and the rearrangement produces a ring chromosome. isochromosomes form when the centromere divides along the transverse plane rather than the normal long axis of the chromosome so that both arms are identical. All of the previously described structural abnormalities can affect both autosomal and sex chromosomes.

The causes of chromosomal errors are not completely understood. In some conditions such as Down syndrome, late maternal age seems to be a factor. Other factors may include the predisposition of chromosomes to nondisjunction (failure to separate during meiosis), exposure to radiation, and viruses.
homologous c's the chromosomes of a matching pair in the diploid complement that contain alleles of specific genes.
Ph1 chromosome (Philadelphia chromosome) an abnormality of chromosome 22, characterized by the translocation of genetic material from its long arm to chromosome 9, seen in the marrow cells of most patients with chronic myelogenous leukemia.
ring chromosome a chromosome in which both ends have been lost (deletion) and the two broken ends have reunited to form a ring-shaped figure.
sex c's the chromosomes responsible for determination of the sex of the individual that develops from a zygote; in mammals they are an unequal pair, the X and Y chromosomes.
somatic chromosome autosome.
X chromosome the female sex chromosome, being carried by half the male gametes and all female gametes; female diploid cells have two X chromosomes.
Y chromosome the male sex chromosome, being carried by half the male gametes and none of the female gametes; male diploid cells have an X and a Y chromosome.

Y chromosome

or

Y-chromosome

(wī′krō′mə-sōm′)
n.
The sex chromosome associated with male characteristics in mammals, not occurring in females and occurring with one X chromosome in the male sex-chromosome pair.

Y chromosome

a sex chromosome that in humans and many other animals is present only in the male, appearing singly in the normal male. It is present in one half of the male gametes and none of the female gametes, is much smaller than the X chromosome, and has genes associated with triggering the development and differentiation of male characteristics. Compare X chromosome.

Y chromosome

A chromosome that contains the genetic information needed to produce a male, which is found in half of sperm cells.

Y chromosome

The sex chromosome of normal ♂. Cf X chromosome.
X chromosome
sex chromosomes.,
, Y chromosome (krō'mŏ-sōm)

Y chromosome

the chromosome which causes the medulla of the embryonic gonad to form a testis. If there is one other chromosome present and it is X the newborn animal will be a fertile male. If there are two other X chromosomes, giving an XXY configuration, it will be a phenotypic male but sterile. Autosomal genes can have the same effect, creating an intersex newborn in an animal with XX chromosomes.
References in periodicals archive ?
The research suggests that the Y chromosome has optimized production from genes that are necessary for making males.
Conversely, a palindrome on the Y chromosome will be selected for because it provides a duplicate copy of the genes it contains, enabling them to be maintained.
Using evidence from the distribution of the Y Chromosomes, Jeffrey T.
The problem is to be sure that this is the personal Y chromosome of Genghis Khan," adds Jaume Bertranpetit of the University of Pompeu Fabra in Barcelona.
Y chromosomes are probably lost when cells divide, with some cells failing to divvy up their chromosomes equally.
We don't know what selection and population structure are doing to the Y chromosome," says geneticist Rosalind M.
Just what might have happened to the Y chromosome in XY females also interests Jennifer A.
Lyon suggested, for example, that females wouldn't inactivate an X chromosome gene if it had a counterpart on the Y chromosome.
Still, the method yields a sperm sample in which 65 percent carry the Y chromosome, Fugger says.
Two recent studies by Skorecki and several of his colleagues find that the cohanim indeed have some Y chromosome features distinct from other Jews.
However, he predicted that the Y chromosome in long-eyed males can resist the selfish X and so create an unusual number of sons.
When sperm are produced in men, however, only a part of the Y chromosome, perhaps 5 percent, can recombine with its partner, the X chromosome.