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14 - C THE NUCLEUS CHROMOSOMES AND EXPRESSION OF THEIR...

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C THE NUCLEUS, CHROMOSOMES, AND EXPRESSION OF THEIR GENES Genomic DNA in most of the animals of interest to the reader consists of approximately 3-4 billion base-pairs of nucleotides arranged as linear polymers, in a variable number of chromosomes. Somatic cells (i.e. non-gametes) have a pair of sex chromosomes along with characteristic numbers of paired autosomes where each chromosome within the pair is derived from each of the two parents. In mammals where the sire's gamete determines sex of the offspring, males possess an X and a Y chromosome, the Y being paternally- derived. Female offspring result from the sire contributing an X chromosome to the X present in the oocyte, resulting in an XX karyotype. Avian sex determination is the responsibility of the female parent and the non-autosomal chromosomes are called WZ in females and ZZ in the homogametic males. 2007 version – page 99
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