As crossing over occurs when gametes are secreted, so when a zygote is formed after fertilization, the base pairs of DNA in the child should be different from that of the parents. So when gel electrophoresis occurs, the position of DNA fragments of the child shouldn't be the same as half of their father and mother. But why is this statement wrong? sorry for bad English.


1 Answer 1


Crossing over is an event that occurs during meiosis, which produces the gametes. This crossing over occurs between 2 homologous chromosomes, which are both from the parent. Hence, even though crossing over occurs, the recombinant chromosome that is passed down to the child will contain an allele that matches with the allele on one of the parent's chromosomes. Within the allele, the base pair sequence would not change.

  • $\begingroup$ So it means that the allele extracted from the child should be the same as the parents to attain the same base pair sequence? i.e. tandem repeat? Thank you very much $\endgroup$
    – Tony1300
    Commented Jun 28, 2019 at 14:16
  • $\begingroup$ Yes, the same allele should be targeted in the child as in the parent. This would ensure that the size of the DNA fragments obtained are the same, so the position of the DNA bands on the gel would also be the same. $\endgroup$
    – kainesu
    Commented Jun 29, 2019 at 10:37

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