In: Biology
A single, non-disjunction event involving chromosome 1a occurs during cell division. Describe how this event would affect the chromosomal complement of the specified cells in the following situations:
a) Daughter cells if non-disjunction occurs during Mitosis.
b) Gametes if non-disjunction occurs during Meiosis I.
c) Gametes if non-disjunction occurs during Meiosis II.
a) In mitosis, there is a separation of sister chromatids into newly formed daughter cells. When non disjunction occurs, atleast one pair of sister chromatids fail to separate from each other in the anaphase. This results in aneuploidy of cells - (2n+1) in some and (2n-1) in others.
b) In meiosis I there is separation of homologous chromosomes. If non disjunction occurs during anaphase I of meiosis I, this means that at least one pair of homologous chromosomes did not separate. This results in two daughter cells carrying an extra chromosome and two daughter cells with one less chromosome. And after meiosis II of the four gametes formed, two will be having an extra chromosome (n+1) and the remaining two will have one chromosome less(n-1).
c) In meiosis II, there is separation of sister chromatids. If non disjunction occurs during anaphase II of meiosis II, it means that atleast one pair of sister chromatids did not separate.Of the four gametes formed, two will have normal haploid number of chromosomes(n), one will have an extra chromosome (n+1) and one will be missing a chromosome (n-1).