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Sex chromosomes (also referred to as allosomes, heterotypical chromosome, gonosomes, heterochromosomes, [1] [2] or idiochromosomes [1]) are chromosomes that carry the genes that determine the sex of an individual. The human sex chromosomes are a typical pair of mammal allosomes. They differ from autosomes in form, size, and behavior.
The first complete telomere-to-telomere sequence of a human autosomal chromosome, chromosome 8, followed a year later. [72] The complete human genome (without Y chromosome) was published in 2021, while with Y chromosome in January 2022. [3] [4] [73] In 2023, a draft human pangenome reference was published. [8]
In the germ-line (the sex cells) the chromosome number is n (humans: n = 23). [4] [5] p28 Thus, in humans 2n = 46. So, in normal diploid organisms, autosomal chromosomes are present in two copies. There may, or may not, be sex chromosomes. Polyploid cells have multiple copies of chromosomes and haploid cells have single copies.
The human Y chromosome showing the SRY gene which codes for a protein regulating sexual differentiation. Sexual differentiation in humans is the process of development of sex differences in humans. It is defined as the development of phenotypic structures consequent to the action of hormones produced following gonadal determination. [1]
Of these 23 pairs of chromosomes, 22 are autosomes, and one is a sex chromosome. [1] There are two kinds of sex chromosomes–X and Y. In humans and in almost all other mammals, females carry two X chromosomes, designated XX, and males carry one X and one Y, designated XY. [1] A human egg contains only one set of chromosomes (23) and is a ...
The human Y chromosome is composed of about 62 million base pairs of DNA, making it similar in size to chromosome 19 and represents almost 2% of the total DNA in a male cell. [54] [55] The human Y chromosome carries 693 genes, 107 of which are protein-coding. [56]
The X chromosome in humans spans more than 153 million base pairs (the building material of DNA). It represents about 800 protein-coding genes compared to the Y chromosome containing about 70 genes, out of 20,000–25,000 total genes in the human genome. Each person usually has one pair of sex chromosomes in each cell.
Genome size ranges (in base pairs) of various life forms. Genome size is the total amount of DNA contained within one copy of a single complete genome.It is typically measured in terms of mass in picograms (trillionths (10 −12) of a gram, abbreviated pg) or less frequently in daltons, or as the total number of nucleotide base pairs, usually in megabases (millions of base pairs, abbreviated ...