Sexual Reproduction

• Fertilization is the process where the male and female gametes come together and their nuclei fuse.

• In animals, fertilization occurs either internally (inside the female's body) or externally (outside the body, like in fish).

• In plants, fertilization occurs when a pollen grain (male gamete) reaches the ovule (female gamete), often through the process of pollination.

• Result of Fertilization:

  • The fusion of the gamete nuclei creates a zygote, which contains a complete set of chromosomes, half from each parent.

  • The zygote undergoes cell division and development to form a new individual.

3. State that nuclei of gametes are haploid and that the nucleus of a zygote is diploid:

• Haploid Gametes:

  • Gametes (sperm and egg) are haploid, meaning they contain half the number of chromosomes of a normal body cell. In humans, gametes have 23 chromosomes (half of the 46 chromosomes in normal body cells).

• Diploid Zygote:

  • When the male and female gametes fuse during fertilization, their haploid nuclei combine to form a diploid zygote, which has the full number of chromosomes (46 in humans).

  • This diploid state ensures that the chromosome number remains constant from generation to generation.

4. Discuss the advantages and disadvantages of sexual reproduction:

(a) To a population of a species in the wild:

• Advantages:

  • Genetic Variation: Sexual reproduction produces offspring with diverse genetic combinations, which is important for the survival of the species, as it increases the chances that some individuals will have traits suited to survive in changing environments.

  • Adaptation to Environmental Changes: Genetic variation allows populations to adapt more readily to new diseases, predators, or other environmental pressures.

• Disadvantages:

  • Energy and Time Consuming: Sexual reproduction requires finding a mate, which can take time and energy. This could be difficult in environments where mates are scarce.

  • Slower Reproduction Rate: Sexual reproduction typically occurs less rapidly than asexual reproduction, as it involves the production and fusion of gametes.

  • Risk of Harmful Genetic Combinations: While genetic variation is an advantage, it can also lead to the combination of harmful genes, resulting in genetic disorders or reduced fitness.

(b) To crop production:

• Advantages:

  • Genetic Diversity: Sexual reproduction in crops can result in new varieties with beneficial traits, such as improved resistance to pests, diseases, or changing weather conditions.

  • Improved Yield and Quality: The introduction of genetic variation may lead to crops with higher yields or better quality.

  • Long-Term Sustainability: Over time, crops produced through sexual reproduction may be more resilient to environmental changes or evolving threats.

• Disadvantages:

  • Slower Process: Sexual reproduction in crops can take longer, as it requires pollination and fertilization, making it slower than asexual reproduction (e.g., cloning or vegetative propagation).

  • Unpredictability: The genetic variation introduced by sexual reproduction can sometimes result in undesirable traits or unpredictable outcomes in crop characteristics.

  • Dependence on Pollinators: Many crops depend on external pollinators (e.g., bees), and their absence or decline can affect crop production.