explain how a zygote could end up with an extra chromosome
please help my book does not explain
Although meiosis typically splits sex cells into the haploid number, every once in a while it is not balanced. One sex cell gets one less, while the other gets one more chromosome. If the cell with an extra chromosome is involved in fertilization, the zygote will have an extra chromosome.
However, since this is not my area of expertise, I searched Google under the key words "'extra chromosome'" to get these possible sources:
http://en.wikipedia.org/wiki/Down_syndrome
http://www.babycenter.com/404_what-does-it-mean-when-a-baby-has-an-extra-chromosome_5279.bc
http://biology.about.com/od/basicgenetics/a/aa110504a.htm
http://hmg.oxfordjournals.org/cgi/content/full/8/12/2205
More information might be available under "trisomy."
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.
I hope this helps. Thanks for asking.
Certainly! When a zygote is formed, it results from the union of sperm and egg during fertilization. Normally, each parent contributes one set of chromosomes to form a complete set in the zygote, with 23 chromosomes from both the mother and father. However, in some cases, errors can occur during the formation of the zygote, leading to an extra chromosome. This condition is known as a chromosomal disorder.
There are a few different ways that a zygote can end up with an extra chromosome:
1. Non-disjunction: Non-disjunction is the most common cause of chromosomal disorders. It occurs when pairs of chromosomes fail to separate properly during cell division, leading to one of the resulting cells receiving an extra chromosome. If this abnormal cell is involved in fertilization, it can result in a zygote with an extra chromosome.
2. Translocation: Translocation involves the exchange of genetic material between non-homologous chromosomes. Sometimes, during this exchange, a fragment of one chromosome may attach to another non-homologous chromosome. This can lead to the formation of a zygote with one extra chromosome.
3. Mosaicism: Mosaicism occurs when there is a mixture of cells with a normal number of chromosomes and cells with an extra chromosome. This can happen if an error in cell division occurs after fertilization, resulting in two distinct cell populations within the same individual. In this case, some cells of the zygote will have a normal chromosome count, while others will have an extra chromosome.
It's important to note that having an extra chromosome can result in various chromosomal disorders, such as Down syndrome (Trisomy 21), where there is an extra copy of chromosome 21. Chromosomal disorders often have significant effects on an individual's development and health.