Sexual differentiation in humans All diploid organisms with allosome-determined sex get half of their allosomes from each of their parents. For a mammal to be chromosomally female, the individual must receive an X chromosome from both parents, whereas to be chromosomally male, the individual must receive a X chromosome from their mother and a Y chromosome from their father. However, a small percentage of humans have a divergent sexual development, known as intersex. This can result from allosomes that are neither XX nor XY.
In most species of animals the sex of individuals is determined decisively at the time of fertilization of the egg, by means of chromosomal distribution. This process is the most clear-cut form of sex determination.
When any cell in the body Sex chromosomes, except… Individuals having two X chromosomes XX are female; individuals having one X chromosome and one Y chromosome XY are male.
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.
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.
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. 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.
The XX/XY sex-determination system is the most familiar, as it is found in humans. The XX/XY system is found in most other mammals, as well as some rutadeltambor.com this system, most females have two of the same kind of sex chromosome (XX), while most males have two distinct sex chromosomes (XY). Sex chromosomes definition, a chromosome, differing in shape or function from other chromosomes, that determines the sex of an individual. See more. May 31, · In the human body, every cell that has a nucleus also carries 23 pairs of chromosomes except the germ cells/ gametes which carry a combination of 22+ X or 22 + Y (only 23 chromosomes)depending on the gender. mature RBCs do not have a nucleus and hence lack chromosomes as well.
See also X trisomy ; XYY-trisomy. Learn More in these related Britannica articles:Sex chromosomes are particular chromosomes that are involved in determining the sex of an organism. In the cells of humans and many other organisms the sex chromosomes consist of a pair of chromosomes called the X and Y chromosomes.
|Sex chromosomes | Define Sex chromosomes at rutadeltambor.com||Sex Chromosomes Photo by:|
|Sex chromosome - Biology-Online Dictionary | Biology-Online Dictionary||X-chromosome Inactivation XCI Human females inherit two copies of every gene on the X chromosome, whereas males inherit only one with some exceptions:|
|Bibliography||Sexual differentiation in humans All diploid organisms with allosome-determined sex get half of their allosomes from each of their parents.|
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 . 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 . Chromosomal basis of sex determination.
X and Y chromosomes, X-linkage. Apr 07, · This feature is not available right now. Please try again later. Humans have 22 chromosome pairs and two sex chromosomes.
Females have two X chromosomes; males have an X chromosome and a Y chromosome.