The correct option for the question "At fertilization" is
C. the male nucleus fuses with the female nucleus.
Detailed Explanation
- Understanding Fertilization:
-
Fertilization is the process where a male gamete (sperm) and a female gamete (egg) unite to form a zygote. This is a crucial step in sexual reproduction, leading to the development of a new organism.
-
Nuclear Fusion:
-
During fertilization, the sperm enters the egg, and the nuclei of both gametes come together. This fusion of the male and female nuclei is what creates a diploid zygote, which contains genetic material from both parents. This is a key event in fertilization, as it combines the genetic information from both the male and female.
-
Chromosome Contribution:
- Each gamete contributes one set of chromosomes. In humans, for example, the sperm contributes 23 chromosomes, and the egg contributes another 23 chromosomes. When these nuclei fuse, the resulting zygote has a total of 46 chromosomes (23 pairs), which is the normal diploid number for humans.
Why the Other Options are Incorrect
- Option A: One chromosome from the male joins another from the female:
-
This statement is misleading because it implies that individual chromosomes are joining rather than the entire nuclei. Fertilization involves the fusion of nuclei, not just the joining of single chromosomes. Therefore, this option does not accurately describe the fertilization process.
-
Option B: One gene from the male combines with another from the female:
-
This option is also incorrect because it oversimplifies the process. While genes do combine during fertilization, the primary event is the fusion of the nuclei, which contains all the chromosomes and genes. Saying that one gene combines with another does not capture the complexity of genetic contribution from both parents.
-
Option D: One set of chromosomes combines with another set from the female:
- While this statement is partially true, it is not as precise as option C. It suggests that the sets of chromosomes are merely combining rather than emphasizing the critical event of nuclear fusion. The focus should be on the fusion of the male and female nuclei, which is the defining characteristic of fertilization.
Summary of Key Points
- Fertilization involves the fusion of the male and female nuclei, leading to the formation of a zygote.
- Each gamete contributes one set of chromosomes, resulting in a diploid organism.
- The process is more complex than simply combining individual chromosomes or genes.
- Understanding the role of nuclear fusion is crucial for grasping the fundamentals of sexual reproduction.
Revision Summary
- Fertilization is the fusion of male and female gametes, resulting in a zygote.
- The male and female nuclei combine, contributing genetic material from both parents.
- Each gamete contributes one set of chromosomes, leading to a diploid zygote.
- The focus of fertilization is on nuclear fusion, not just the joining of chromosomes or genes.