Meiosis, Germ Cells, and Fertilization
Meiosis, Germ Cells, and Fertilization
Meiosis, Germ Cells, and Fertilization
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EGGS<br />
• once activated, it can give rise to a complete new individual<br />
• Activation is usually the consequence of fertilization (fusion of a sperm with<br />
the egg).<br />
• Some lizards’ eggs become activated in the absence of sperm<br />
(parthenogenetically).<br />
• Mammals cannot; because of genomic imprinting (they require both<br />
maternal <strong>and</strong> paternal genetic contributions).<br />
• The cytoplasm of an egg can even reprogram a somatic cell nucleus so that<br />
the nucleus can direct the development of a new individual.<br />
• Reproductive cloning has been used to produce clones of various mammals.<br />
• Less than 5% of them develop to adulthood
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