<P> The idea that the X chromosome was named after its similarity to the letter "X" is mistaken . All chromosomes normally appear as an amorphous blob under the microscope and only take on a well defined shape during mitosis . This shape is vaguely X-shaped for all chromosomes . It is entirely coincidental that the Y chromosome, during mitosis, has two very short branches which can look merged under the microscope and appear as the descender of a Y - shape . </P> <P> It was first suggested that the X chromosome was involved in sex determination by Clarence Erwin McClung in 1901 after comparing his work on locusts with Henking's and others . McClung noted that only half the sperm received an X chromosome . He called this chromosome an accessory chromosome and insisted, correctly, that it was a proper chromosome, and theorized, incorrectly, that it was the male determining chromosome . </P> <P> Luke Hutchison noticed that a number of possible ancestors on the X chromosome inheritance line at a given ancestral generation follows the Fibonacci sequence . A male individual has an X chromosome, which he received from his mother, and a Y chromosome, which he received from his father . The male counts as the "origin" of his own X chromosome (F 1 = 1 (\ displaystyle F_ (1) = 1)), and at his parents' generation, his X chromosome came from a single parent (F 2 = 1 (\ displaystyle F_ (2) = 1)). The male's mother received one X chromosome from her mother (the son's maternal grandmother), and one from her father (the son's maternal grandfather), so two grandparents contributed to the male descendant's X chromosome (F 3 = 2 (\ displaystyle F_ (3) = 2)). The maternal grandfather received his X chromosome from his mother, and the maternal grandmother received X chromosomes from both of her parents, so three great - grandparents contributed to the male descendant's X chromosome (F 4 = 3 (\ displaystyle F_ (4) = 3)). Five great - great - grandparents contributed to the male descendant's X chromosome (F 5 = 5 (\ displaystyle F_ (5) = 5)), etc . (Note that this assumes that all ancestors of a given descendant are independent, but if any genealogy is traced far enough back in time, ancestors begin to appear on multiple lines of the genealogy, until eventually, a population founder appears on all lines of the genealogy .) </P> <P> 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 . Females have two X chromosomes, whereas males have one X and one Y chromosome . Both males and females retain one of their mother's X chromosomes, and females retain their second X chromosome from their father . Since the father retains his X chromosome from his mother, a human female has one X chromosome from her paternal grandmother (father's side), and one X chromosome from her mother . This inheritance pattern follows the Fibonacci numbers at a given ancestral depth . </P>

Where does a female get her x chromosome from
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