As the cells of an early female embryo divide they randomely inactivate one of the two X chromosomes. By chance, some cells end up with an active X from their mother, and others the X chromosome they received from their father. As the embryo develops, the descendants of the early dividing cells will inherit the same paternal or maternal active X chromosomes and the specific gene forms on those chromosomes. On average, half of the cells express their maternal X and half express their paternal X. The result of X inactivation is a mosaicism of expressed X-linked traits.
Certain genes, can reveal the mosaicism visually, for example in the case of tortoise shell cats. The gene for coat color is on the X chromosome. When the cat is heterozygous in coat color (black/orange) it is born with patches of different colored fur on its body.
X Inactivation Teaching Tips
The animations in this section have a wide variety of classroom applications. Use the tips below to get started but look for more specific teaching tips in the near future. Please tell us how you are using the animations in your classroom by sending e-mail to firstname.lastname@example.org.
Use the animations to make abstract scientific ideas visible and concrete.
Explain important scientific principles through the animations. For example, the biological clocks animations can be used to demonstrate the fundamentals of transcription and translation.
Make sure that students learn the material by repeating sections of the animations as often as you think necessary to reinforce underlying scientific principles. You can start, restart, and play back sections of the animations.
Urge students to use the animations in accordance with their own learning styles. Students who are more visually oriented can watch the animations first and read the text later, while others might prefer to read the explanations first and then view the graphics.
Incorporate the animations into Web-based learning modules that you create to supplement your classroom curricula.
Encourage students to incorporate the animations into their own Web-based projects.
X Inactivation Background
From Lecture 4 of the 2003 Holiday Lectures Series "Learning From Patients: The Science of Medicine."