Suppose you read in the newspaper that a genetic engineering laboratory has developed a procedure for fusing two gametes from the same person (two eggs or two sperm) to form a zygote. The article mentions that an early step in the procedure prevents crossing over from occurring during the formation of the gametes in the donor's body. The researchers are in the process of determining the genetic makeup of one of their new zygotes. Which of the following predictions do you think they would make? Justify your choice, and explain why you rejected each of the other choices.
a. The zygote would have 46 chromosomes, all of which came from the gamete donor (its one parent), so the zygote would be genetically identical to the gamete donor.
b. The zygote could be genetically identical to the gamete donor, but it is much more likely that it would have an unpredictable mixture of chromosomes from the gamete donor's parents.
c. The zygote would not be genetically identical to the gamete donor, but it would be genetically identical to one of the donor's parents.
d. The zygote would not be genetically identical to the gamete donor, but it would be genetically identical to one of the donor's grandparents.

Verified step by step guidance

1. Step 1: Understand the concept of gametes and zygotes. Gametes (sperm and egg cells) are haploid cells, meaning they contain half the number of chromosomes (23 in humans). A zygote is formed when two gametes fuse, resulting in a diploid cell with 46 chromosomes. In this scenario, the gametes are from the same individual, and crossing over is prevented during gamete formation.
2. Step 2: Analyze the implications of preventing crossing over. Crossing over is a process during meiosis where homologous chromosomes exchange genetic material, increasing genetic diversity. If crossing over is prevented, the gametes will contain chromosomes that are exact copies of the donor's original chromosomes, without any recombination.
3. Step 3: Consider the genetic makeup of the zygote formed by fusing two gametes from the same individual. Since the gametes are from the same person and crossing over is prevented, the zygote will inherit chromosomes that are a combination of the donor's maternal and paternal chromosomes. However, the arrangement of chromosomes in the zygote will depend on how the chromosomes segregated during meiosis.
4. Step 4: Evaluate each choice based on the information provided: (a) The zygote would not be genetically identical to the gamete donor because the zygote is formed by combining two gametes, which may have different combinations of the donor's maternal and paternal chromosomes. (b) This choice is plausible because the zygote could have a mixture of chromosomes from the donor's parents, but the exact combination is unpredictable due to random segregation during meiosis. (c) The zygote would not be genetically identical to one of the donor's parents because it contains chromosomes from both parents. (d) The zygote would not be genetically identical to one of the donor's grandparents because it does not directly inherit chromosomes from the grandparents.
5. Step 5: Conclude that the most likely prediction is choice (b). The zygote could be genetically identical to the gamete donor, but it is much more likely to have an unpredictable mixture of chromosomes from the donor's parents due to random segregation during meiosis. This choice aligns with the biological principles of gamete formation and zygote development.

Key Concepts

Gametes and Zygotes

Gametes are the reproductive cells (sperm and eggs) that carry half the genetic information of an organism. When two gametes fuse during fertilization, they form a zygote, which contains a complete set of chromosomes, half from each parent. In this scenario, the zygote is formed from two gametes from the same individual, leading to a unique genetic outcome.

Crossing Over

Crossing over is a process that occurs during meiosis, where homologous chromosomes exchange genetic material. This process increases genetic diversity by creating new combinations of alleles. The article mentions that crossing over is prevented, meaning the gametes will retain the same genetic information as the donor, which is crucial for understanding the genetic makeup of the resulting zygote.

Genetic Identity

Genetic identity refers to the genetic similarity between individuals. In this case, since the zygote is formed from two gametes of the same donor, it will have a complete set of chromosomes from that single individual, making it genetically identical to the donor. This concept is essential for predicting the genetic outcome of the zygote in the context of the question.