
Concept explainers
BPA and Abnormal Meiosis In 1998, researchers at Case Western University were studying meiosis in mouse oocytes (germ cells) when they saw an unexpected and dramatic increase of abnormal events (FIGURE 12.6). Improper segregation of chromosomes during meiosis is one of the main causes or human genetic disorders.
The spike in abnormal meiosis began right after the mouse facility started washing the animals' plastic cages and water bottles in a new, alkaline detergent. The detergent had damaged the plastic, which as a result was leaching bisphenol A (BPA). BPA is a synthetic chemical that mimics estrogen, the main female sex hormone in animals. Though it has since been banned for use in baby bottles, BPA is still widely used to manufacture other plastic items and epoxies (such as the coating on the inside of metal cans of food). BPA-free plastics are often manufactured with a related compound, bisphenol S (BPS), that has effects similar to BPA.
FIGURE 12.6 Abnormalities in meiosis that occurred after exposure to BPA.
Top, the most abnormal meiosis events occurred in mice that were housed in damaged plastic caging with damaged plastic bottles. Damaged plastic releases BPA.
Bottom, fluorescent micrographs show the chromosomes (red) and spindle (green) in nuclei of mouse germ cells in metaphase I. A Normal metaphase; B–D abnormal metaphase.
What percentage of mouse oocytes displayed abnormalities of meiosis with no exposure to damaged caging?

To determine: The percentage of the mice that had the most abnormalities in their oocytes with no exposure to damaged caging.
Introduction: A synthetic chemical called bisphenol A (BPA) imitates the female sex hormone—estrogen that is found in the animals. Bisphenol A is used in the manufacturing of different plastics including polycarbonate plastics such as dental sealants, baby bottles, and food and drink containers. Research studies show that these chemicals possess the capability to disrupt the meiotic division and then damage the reproductive function of the organism (experiments conducted in the mice oocytes).
Explanation of Solution
In the given experiment, researchers had found that a changed alkaline detergent caused damage to the plastic and resulted in the leaching of BPA chemical. BPA that mimics as estrogen hormone induces meiotic abnormalities in the mice oocyte.
The experiment was conducted with a plastic damaged cage and a new cage as the control. Along with that, they used glass bottles as control with the damaged one. The study showed the following:
- Abnormalities in mice oocyte placed in a new cage with glass bottle were 1.8%.
- Mildly damaged cage with glass bottles were 8.7%, and severely damaged cage with glass bottles was 20.1%.
- The abnormalities associated with damaged plastic bottles alone were 26.9%.
- In the damaged cages with the damaged plastic bottles, it was observed that the abnormality rates were 41.4%.
Out of 271 mice oocytes, only 5 out of them showed the abnormalities. When this was converted to a percentage, it accounts for about 1.8%. Hence, the researchers concluded that the mice oocytes that had most abnormalities of meiosis with no exposure to the damaged cage were about 1.8%.
About 1.8% of mice oocytes that were exposed to damaged cages had most abnormalities of meiosis.
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