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In the XY sex-determination system, the female-provided ovum contributes an X chromosome and the male-provided sperm contributes either an X chromosome or a Y chromosome, resulting in female (XX) or male (XY) offspring, respectively. Hormone levels in the male parent affect the sex ratio of sperm in humans. [25]
The sex chromosome in a human egg is always an X chromosome since a female only has X sex chromosomes. In sperm, about half the sperm have an X chromosome and half have a Y chromosome. [2] If an egg fuses with sperm with a Y chromosome, the resulting individual is male.
In the absence of a Y chromosome, the fetus will undergo female development. This is because of the presence of the sex-determining region of the Y chromosome, also known as the SRY gene. [5] Thus, male mammals typically have an X and a Y chromosome (XY), while female mammals typically have two X chromosomes (XX).
However, when an extra DAX1 gene is placed on the X chromosome, the result is a female, despite the existence of SRY, since it overrides the effects of SRY. [11] Even when there are normal sex chromosomes in XX females, duplication or expression of SOX9 causes testes to develop.
Male sterility likely arises first as an adaptation to prevent selfing. Once male sterility has reached a certain prevalence, then female sterility may have a chance to arise and spread. [13] In the domesticated papaya (Carica papaya), three sex chromosomes are present, denoted as X, Y and Y h. This corresponds with three sexes: females with XX ...
The Y chromosome is one of two sex chromosomes in therian mammals and other organisms.Along with the X chromosome, it is part of the XY sex-determination system, in which the Y is the sex-determining chromosome because the presence of the Y chromosome causes offspring produced in sexual reproduction to be of male sex.
Females normally have two X chromosomes while males typically have an X and a Y chromosome. The X chromosome is more active and encodes more information than the Y chromosome, which has been shown to affect behavior. [14] Genetic researchers theorize that the X chromosome may contain a gene influencing social behaviours. [15] [better source needed]
Female cells may express higher levels of some genes. [29] [30] [31] Sex differences at the chromosome and molecular level exist in all human cells, and persist life-long, independent of sex hormones in the body. [5] Sex-linked genetic conditions that differ in males and females may reflect the effects of genetic damage on an X chromosome. In ...