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Sperm also have only one set of 23 chromosomes and are therefore haploid. When an egg and sperm fuse at fertilization, the two sets of chromosomes come together to form a unique diploid individual with 46 chromosomes. [2] The sex chromosome in a human egg is always an X chromosome since a female only has X sex chromosomes.
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).
Early in female embryonic development, in cells other than egg cells, one of the X chromosomes is randomly and permanently partially deactivated: In some cells, the X chromosome inherited from the mother deactivates; in other cells, it is the X chromosome inherited from the father. This ensures that both sexes always have exactly one functional ...
This is an accepted version of this page This is the accepted version, checked on 12 January 2025. There are template/file changes awaiting review. DNA molecule containing genetic material of a cell This article is about the DNA molecule. For the genetic algorithm, see Chromosome (genetic algorithm). Chromosome (10 7 - 10 10 bp) DNA Gene (10 3 - 10 6 bp) Function A chromosome and its packaged ...
Sexual dimorphism is a term for the genotypic and phenotypic differences between males and females of the same species. Through the process of meiosis and fertilization (with rare exceptions), each individual is created with zero or one Y-chromosome. The complementary result for the X-chromosome follows, either a double or a single X.
Differences between gametes and somatic cells [ edit ] In contrast to a gamete, which has only one set of chromosomes, a diploid somatic cell has two sets of homologous chromosomes , one of which is a copy of the chromosome set from the sperm and one a copy of the chromosome set from the egg cell.
This and other factors result in the sex differences in humans. [9] The cells in females, with two X chromosomes, undergo X-inactivation, in which one of the two X chromosomes is inactivated. The inactivated X chromosome remains within a cell as a Barr body.
In female cells, random processes of X-inactivation "turn off" the extra X chromosome. As a result, females, but not males, are mosaics. 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 ...