#3) A person with trisomy 21 has an extra copy of chromosome 21. What happened during meiosis that caused the person to get three, instead of two, copies of chromosome 21?
A) nondisjunction
B) genetic recombination
C) Binary fission
D) Crossing Over
I'm thinking that sounds like C... but I'm not one hundred percent sure.
Trisomy 21 (47,XX,+21) is caused by a meiotic nondisjunction event.
oh... okay, thanks
The correct answer is A) nondisjunction.
During meiosis, which is a specialized cell division process that produces gametes (eggs or sperm), two rounds of division occur. In the first round of division, called meiosis I, homologous chromosomes pair up and separate, resulting in two daughter cells with half the number of chromosomes as the original cell. In the second round of division, called meiosis II, the sister chromatids of each chromosome separate, resulting in four daughter cells with half the number of chromosomes as the original cell.
Nondisjunction is an error that can occur during meiosis I or meiosis II, where the homologous chromosomes or sister chromatids fail to separate correctly. In the case of a person with trisomy 21, nondisjunction occurred during meiosis, leading to an extra copy of chromosome 21 being present in one of the resulting gametes (egg or sperm). If this gamete is involved in fertilization, the resulting embryo will have three copies of chromosome 21 instead of the usual two.
To determine the correct answer to this question, it is important to understand the process of meiosis and the consequences of different meiotic errors. In this case, nondisjunction is the specific error that causes the individual to have three copies of chromosome 21. Incorrect answers such as genetic recombination, binary fission, and crossing over are not directly related to the specific error of having an extra chromosome.