Answer: sex chromosoem found in human males but not females
y chromosome
In humans the Y chromosome spans about 58 million base pairs (the building blocks of DNA) and represents almost 2% of the total DNA in a male cell. The human Y chromosome contains over 200 genes at least 72 of which code for proteins.
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The Y chromosome is one-third the size of the X chromosome and contains about 55 genes while the X chromosome has about 900 genes. In genealogy the male lineage is often traced using the Y chromosome because it is only passed down from the father.
The X and Y chromosomes also known as the sex chromosomes determine the biological sex of an individual: females inherit an X chromosome from the father for a XX genotype while males inherit a Y chromosome from the father for a XY genotype (mothers only pass on X chromosomes). The presence or absence of the Y chromosome is critical because it contains the genes necessary to override the biological default - female development - and cause the development of the male reproductive system.
The Y chromosome is one of the two sex chromosomes in humans (the other is the X chromosome ). The sex chromosomes form one of the 23 pairs of human chromosomes in each cell. The Y chromosome spans more than 59 million building blocks of DNA (base pairs) and represents almost 2 percent of the total DNA in cells.
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