MEIOTIC MISHAPS

Meiosis consists of two cell divisions that ultimately result in four haploid daughter cells. The reduction of genetic material from diploid to haploid takes place in meiosis I when maternal and paternal members of homologous pairs separate. The second division of meiosis occurs very much like mitosis.

When producing gametes through meiosis, it is imperative that the genetic material be replicated and appropriately partitioned to daughter cells. If the genetic material is not distributed correctly, gametes with the wrong number of chromosomes are produced. The causes and consequences of these errors are the focus of this activity.

ACTIVITY

First you will utilize a portion of an online tutorial about chromosome errors. The University of Illinois College of Medicine provides the tutorial as part of a medical genetics course. Next, you will access medical genetics information provided by Lucile Packard Children’s Hospital.

Part 1.

Use your browser to go to the M1-Medical Genetics page at http://www.med.uiuc.edu/m1/genetics/. Click the "Tutorials" link, then the "Chromosomal Errors" link, then the link to the meiotic errors portion of the tutorial.

Go through the tutorial, then use what you have learned to answer the following questions:

  1. How does the frequency of errors vary between the two meiotic divisions?
  2. What is the effect of maternal age on the frequency of meiotic errors during each division? What could account for this?
  3. What are cohesins and what is their role in meiosis?
  4. How can researchers determine whether an error occurred during meiosis I or meiosis II?

Part 2.

Use your browser to go to the Chromosome Abnormalities page on the Lucile Packard Children’s Hospital site at http://www.lpch.org/DiseaseHealthInfo/HealthLibrary/genetics/chromhub.html.

Focus your attention on the information in the link entitled "How Chromosome Abnormalities Happen: Meiosis, Mitosis, Maternal Age, Environment."

Use the information in this section to answer the following questions:

  1. Define the terms "trisomy" and "monosomy."
  2. How common are chromosome abnormalities among first trimester miscarriages? Among stillbirths?
  3. What evidence is there that environmental factors cause chromosome abnormalities?