Question

which of the following might result in a human zygote with 45 chromosomes?
A) an error in either egg or sperm meiotic anaphase
B) failure of the egg nucleus to be fertilized by the sperm
C) fertilization of a 23 chromosome human egg by a 22 chromosome sperm of a closely related species
D) an error in the alignment of chromosomes on the metaphase
E) lack of chiasmata in prophase 1

Answer 1

A) in the anaphase an event known as nondisjunction can occur that results in the uneven separation of sister chromatids, if this occurs in meiosis 2, all resulting gametes will have abnormal number of chromosomes inside them. (Gametes like sperm and eggs) so when the fusion of abnormal sperm or egg occurs with another sperm/egg, the resulting zygote will have an abnormal amount of chromosomes

here's a link to an example about down syndrome that results from a nondisjunction event
http://www.biology.iupui.edu/biocourses/N100/2k2humancsomaldisorders.html

Answer 2

c