Review the “BPA disrupts human egg maturation” published in a press release by B

Question

Review the “BPA disrupts human egg maturation” published in a press release by Brigham and Women’s Hospital: https://www.eurekalert.org/pub_releases/2013-07/bawh-bed073013.php

In summary, BPA (Bisphenol-A), a compound that was routinely used in plastics including reusable water bottles, food containers, and cash receipts, was found to hinder the ability of chromosomes to separate into four haploid cells during meiosis, thus resulting in complications of egg maturation. Keeping in mind what you have learned this week in terms of meiosis and nondisjunction, what might be the effects seen in offspring resulting from those eggs? In your response, please briefly summarize the process of meiosis, define nondisjunction, and explain the resulting genetic anomalies that may be possible.

Explanation / Answer

Answer: - Meiosis is the specialized version of cell division that occurs only in the testes and ovaries; the organs that produce sperms and eggs respectively. It is a  form of eukaryotic cell division that produces haploid sex cells or gametes from diploid cells. In meiosis, a single cell divides twice to produce four cells. It can be divided into nine stages comprising meiosis 1 and meiosis 2. Meiosis I segregates homologous chromosomes and changes the ploidy of cells from diploid to haploid, therefore known as reduction division. Meiosis II is an equational division similar to mitosis, in which the sister chromatids are segregated, giving rise to four haploid daughter cells.

If the normal separation of chromosomes during meiosis 1 and sister chromatids during meiosis 2 occurs then it is known as disjunction and if somehow this segregation is not normal it is known as nondisjunction. This ultimately results in the production of gametes with an imbalance of chromosomes. Loss of a single chromosome (2n-1) will result in monosomy and gain of a single chromosome (2n+1) will result in trisomy. Turner syndrome is an example of monosomy and Down syndrome is an example of trisomy.

In the example given in the question if the compound hinders the ability of chromosomes to separate into four haploid cells during meiosis then it will either result in monosomy or trisomy and offsprings born will not be viable except in some cases/ Down syndrome is one such example which is a trisomy of the smallest chromosome (chromosome no. 21). Offspring born with such syndromes have severe developmental disorders.

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