The Sex Chromosome ( X And Y ) Originates From A Pair Of Autosomes Essay

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INTRODUCTION:
The Sex chromosome(X and Y) originates from a pair of autosomes (H.J. Muller, 1914) about 350million years ago in reptile-like ancestors (Charlesworth, 1991; Graves, 1995). Environmental factor like temperature determines sex in some species e.g. crocodiles and turtles (Bull et al, 1975). In humans, there are 22 pairs of chromosomes called the Autosomes and one pair of sex chromosome (X-Y) which makes a total of 23pairs of chromosomes. These 23pairs (46) chromosomes are contributed by female and male gamete. Females have 22pairs of autosomes and one sex chromosome (X) while males have Y sex chromosome in addition to the 22pairs of autosomes. This means that, the Y chromosome can only be inherited paternally (Lahn & Page, 1999).
The X-chromosome is about a 165mega base in size and contains about 1000 functional genes (Ross et al, 2005) while Y chromosome is about 65mega base in size with about 178genes (Skalestsky et al; 2003).The Mammalian Y-chromosome contains 86 genes which code for specific proteins with peculiar functions in sex fertility (Lahn & Page, 1997). The Y chromosome is the most evolving part of the human and chimpanzee genome. ‘’The Y chromosome is far superior in the evolutionary progress than the entire human genetic code combined’’ (Dr Page, 2001). The Y chromosome is said to be the smallest chromosome in humans and contain more genes with mutation (Heinkchen, 2005).
“The Primitive Y chromosome was found in Papaya” (Liu et al, 2004) and the Y

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