Question

The cell shown above is a diploid cell (2n = 8) in the testes of a laboratory fish. This laboratory species has been engineered such that there is no crossing over during gamete formation.

Two sperm, that formed independently from the same male laboratory fish, were fused together to form a zygote. (sperm + sperm --> zygote).

A. Which of these is true about the zygote based on the information above?

B. The zygote would have 8 chromosomes, all of which came from the male fish, so the zygote would be genetically identical to the adult male fish.

C. The zygote would not be genetically identical to the adult male fish, but it would be genetically identical to one of the male fish’s parents.

D. The zygote could be genetically identical to the adult male fish, but it’s much more likely to have an unpredictable mixture of chromosomes from the male fish’s parents.

Answer 1

As the gametes of are formed without crossing over in the testes of the laboratory fish, the sperms of the same laboratory fish are being fused to form a zygote. This zygote will be the same as the adult male fish and will be genetically identical to it as the two copies of the chromosomes of the male fish are being fused to form the diploid number of the parent. Hence the correct option will be:

The zygote would have 8 chromosomes, all of which came from the male fish, so the zygote would be genetically identical to the adult male fish.

The other two options which are :

The zygote would not be genetically identical to the adult male fish, but it would be genetically identical to one of the male fishs parents is false as the sperms are each one copy of the chromosome and only one parent is present so this statement is false.

The zygote could be genetically identical to the adult male fish, but it’s much more likely to have an unpredictable mixture of chromosomes from the male fish’s parents. To be unpredictable mixture of chromosomes, the fusion should have recombination event but it doesn't have any recombination event. Hence this statement is also false.

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