Chapter 9 Web links and web activities

Germ cells, fertilization, and sex

Germ Cells migrate from their site of origin to the gonad 
The companion web site to the popular NOVA movie “Life’s Greatest Miracle” allows you to watch the entire movie; featuring the microimagery of Swedish photographer Lennart Nilsson tracking human development.

  • Explore the tutorial “How is Sex Determined?” What route do human stem cells take during their migration to the developing gonads? What crucial event occurs during the 6th week of development that specifies differentiation of male versus female gonads?
  • Explore the tutorial “How Cells Divide: Mitosis vs. Meiosis”. Compare and contrast mitosis and meiosis.

Some genes controlling embryonic growth are imprinted 
The phenomenon of genomic imprinting allows for certain genes in eggs and sperm to be specifically programmed to be switched off during development (see page 411 in Wolpert text). Visit this site developed by the Jirtle Laboratory at Duke University explore the following questions:

  • What disorders are associated with imprinted genes? Click on the “Genes” link at the top of the page; there you will find a long list of gene names. Copy one (any one!) and go to the Online Mendelian Inheritance in Man site (OMIM): . Enter the gene name in the search box at the top, and check out the resultant page for a wealth of information about the gene, including, in a surprising number of cases, a disease that is associated with the gene.
  • What are the implications for the use of assisted reproductive technologies (in vitro fertilization) in light of human imprinting patterns? Go to “Features” at the top of the page, and then “Assisted Reproductive Technology: Cautionary Signs ” in the “Feature Archives” at the right. For further explanation of the possible connection between ART and certain developmental problems, listen to the National Public Radio reports, using the link at the top of the article.