Question

A hammerhead shark that gave birth in a Nebraska aquarium reproduced without mating, ….Instead, the female shark’s own genetic material combined during the process of cell division that produces an egg. A cell called the secondary oocyte, which contains half the female chromosomes and normally becomes the egg, fused with another cell called the secondary polar body…. Now assume that more than one gene is heterozygous. Looking at the two scenarios in the questions above what would be the genetic evidence to support one or the other (what would you expect in terms of genotypes over many genes compared to the mother in either scenario)?

Answer 1

For this we have to be clear on what a secondary oocyte is, and we also have to be clear on what exactly happens in each meiotic division stage. But there seems to be an issue with this question, your teacher is making some mistakes that actually lead to making no sense. The secondary polar body is created when the secondary oocyte has already undergone Meiosis II, thus there is no more secondary oocyte but a mature functional egg. Also, the 2 scenarios are actually not really clear stated there.

We are going to work with the 2 main different parthenogenic processes and their different result in heterozygosity/homozygosity.

These are the 2 scenarios:

1.- The resulting baby shark is heterozygous for one or more traits. The genetic evidence indicates that this parthenogenic event occurred when the secondary oocyte went through Meiosis II and produced a mature egg and a secondary polar body, then these 2 fused and formed the baby shark. Another possibility is that a primary oocyte (before undergoing Meiosis I), never entered Meiosis, and it just started to develop as a new baby shark

2.- The resulting shark baby is homozygous for every trait. The genetic evidence indicates that this parthenogenic event ocurred when a secondary oocyte went through Meiosis II and produced a mature egg and a secondary polar body, then the mature egg replicated its genome to gain diploidy and then developed into a new baby shark. Since this shark made its diploidy by replciating an haploid genome, it will be homozygous for every trait