name an organism in which sex determination is regulated on heredity?give reason
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A sex-determination system is a biologicalsystem that determines the development of sexual characteristics in an organism. Most organisms that create their offspring using sexual reproduction have two sexes. Occasionally, there are hermaphrodites in place of one or both sexes. There are also some species that are only one sex due to parthenogenesis, the act of a female reproducing without fertilization.
In many species, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual morphology. In animals this is often accompanied by chromosomal differences, generally through combinations of XY, ZW, XO, ZO chromosomes, or haplodiploidy. The sexual differentiation is generally triggered by a main gene (a "sex locus"), with a multitude of other genes following in a domino effect.
In other cases, sex is determined by environmental variables (such as temperature) or social variables (e.g. the size of an organism relative to other members of its population).
Some species do not have a fixed sex, and instead change sex based on certain cues. The details of some sex-determination systems are not yet fully understood.
Chromosomal systems
XX/XY sex chromosomes

Drosophila sex-chromosomes

Human male XY chromosomes after G-banding
Main article: XY sex-determination system
Main article: Sexual differentiation in humans
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 insects. In this system, most females have two of the same kind of sex chromosome (XX), while most males have two distinct sex chromosomes (XY). The X and Y sex chromosomes are different in shape and size from each other, unlike the rest of the chromosomes (autosomes), and are sometimes called allosomes. In some species, such as humans, organisms remain sex indifferent for a time after they're created; in others, however, such as fruit flies, sexual differentiation occurs as soon as the egg is fertilized.[1]
Y-centered sex determination
Some species (including humans) have a gene SRY on the Y chromosome that determines maleness. Members of SRY-reliant species can have uncommon XY chromosomal combinations such as XXY and still live.[1] Human sex is determined by the presence or absence of a Y chromosome with a functional SRY gene. Once the SRY gene is activated, cells create testosterone and anti-müllerian hormone which typically ensures the development of a single, male reproductive system.[1] In typical XX embryos, cells secrete estrogen, which drives the body toward the female pathway.
In Y-centered sex determination, the SRY gene is not the only gene to have an influence on sex. Despite the fact that SRY seems to be the main gene in determining male characteristics, it requires the action of multiple genes to develop testes. In XY mice, lack of the gene DAX1 on the X chromosome results in sterility, but in humans it causes adrenal hypoplasia congenita.[2] However, when an extra DAX1 gene is placed on the X, the result is a female, despite the existence of SRY.[3] Also, even when there are normal sex chromosomes in XX females, duplication or expression of SOX9 causes testes to develop.[4][5] Gradual sex reversal in developed mice can also occur when the gene FOXL2 is removed from females.[6] Even though the gene DMRT1 is used by birds as their sex locus, species who have XY chromosomes also rely upon DMRT1, contained on chromosome 9, for sexual differentiation at some point in their formation.[1]
X-centered sex determination
Some species (such as the fruit fly) use the presence of two X chromosomes to determine femaleness.[7] Because the fruit fly, as well as other species, use the number of Xs to determine sex, they are nonviable with an extra X.
In many species, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual morphology. In animals this is often accompanied by chromosomal differences, generally through combinations of XY, ZW, XO, ZO chromosomes, or haplodiploidy. The sexual differentiation is generally triggered by a main gene (a "sex locus"), with a multitude of other genes following in a domino effect.
In other cases, sex is determined by environmental variables (such as temperature) or social variables (e.g. the size of an organism relative to other members of its population).
Some species do not have a fixed sex, and instead change sex based on certain cues. The details of some sex-determination systems are not yet fully understood.
Chromosomal systems
XX/XY sex chromosomes

Drosophila sex-chromosomes

Human male XY chromosomes after G-banding
Main article: XY sex-determination system
Main article: Sexual differentiation in humans
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 insects. In this system, most females have two of the same kind of sex chromosome (XX), while most males have two distinct sex chromosomes (XY). The X and Y sex chromosomes are different in shape and size from each other, unlike the rest of the chromosomes (autosomes), and are sometimes called allosomes. In some species, such as humans, organisms remain sex indifferent for a time after they're created; in others, however, such as fruit flies, sexual differentiation occurs as soon as the egg is fertilized.[1]
Y-centered sex determination
Some species (including humans) have a gene SRY on the Y chromosome that determines maleness. Members of SRY-reliant species can have uncommon XY chromosomal combinations such as XXY and still live.[1] Human sex is determined by the presence or absence of a Y chromosome with a functional SRY gene. Once the SRY gene is activated, cells create testosterone and anti-müllerian hormone which typically ensures the development of a single, male reproductive system.[1] In typical XX embryos, cells secrete estrogen, which drives the body toward the female pathway.
In Y-centered sex determination, the SRY gene is not the only gene to have an influence on sex. Despite the fact that SRY seems to be the main gene in determining male characteristics, it requires the action of multiple genes to develop testes. In XY mice, lack of the gene DAX1 on the X chromosome results in sterility, but in humans it causes adrenal hypoplasia congenita.[2] However, when an extra DAX1 gene is placed on the X, the result is a female, despite the existence of SRY.[3] Also, even when there are normal sex chromosomes in XX females, duplication or expression of SOX9 causes testes to develop.[4][5] Gradual sex reversal in developed mice can also occur when the gene FOXL2 is removed from females.[6] Even though the gene DMRT1 is used by birds as their sex locus, species who have XY chromosomes also rely upon DMRT1, contained on chromosome 9, for sexual differentiation at some point in their formation.[1]
X-centered sex determination
Some species (such as the fruit fly) use the presence of two X chromosomes to determine femaleness.[7] Because the fruit fly, as well as other species, use the number of Xs to determine sex, they are nonviable with an extra X.
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The sex determination of a human is controlled by heredity.
In the XY system, the female ovum which contains X chromosome and the male sperm contains X chromosome or Y chromosome which results in (XX) female or (XY) male offspring respectively. Thus,the sex determination of an human is controlled by heredity.
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