Sexual Reproduction: The Recipe for Diversity

 

What is Sexual Reproduction?

Definition:

• Sexual reproduction is a process involving the fusion of the nuclei of two gametes (sperm and egg in animals or pollen and ovule in plants) to form a zygote.
• Gametes are haploid (contain half the genetic material).
• Zygote is diploid (contains a full set of genetic material).

 

Gametes

• Gametes are specialised sex cells (e.g., sperm and egg in animals, pollen and ovule in plants)
• One of the ways they are specialised is they have a haploid nucleus (contain half the genetic material), so have one copy of each chromosome.
• In humans each cell is supposed to have 46 chromosomes, so gametes will have 23.
• This allows the two gamete cells (sperm and egg) to combine they're genetic material and create a zygote (fertilised egg cell) with the correct number of chromosomes.

 

Key Characteristics

Feature	Description
Number of Parents	Two parents contribute gametes.
Offspring	Genetically different from each other and from the parents (variation).
Gametes	Specialized sex cells (e.g., sperm and egg in animals, pollen and ovule in plants).
Fertilisation	Fusion of male and female gametes to form a zygote.

 

 

Haploid vs Diploid

 

Term	Definition
Haploid (n)	Gametes have half the chromosome number of normal body cells (e.g., sperm, egg).
Diploid (2n)	Zygote has a full set of chromosomes after fertilization.

 

Advantages and Disadvantages of Sexual Reproduction - Extended

 

Advantages
Advantages	Why It’s Good
Genetic Variation	Offspring are unique, increasing adaptability to environmental changes.
Survival Advantage	Some individuals may survive disease or predators due to genetic diversity.
Evolution	Variation allows species to evolve over time.
Disadvantages
Disadvantages	Why It’s Challenging
Slower Process	Requires time and energy to find a mate.
Uncertainty	Fertilisation may not always happen.
Dependent on Two Parents	Both parents must contribute for reproduction to occur.

 

 

Fertilisation: The Key Event

Definition:
Fertilisation is the fusion of the nuclei of gametes (e.g., sperm and egg in animals) to form a zygote.

Step-by-Step Process:

1. Male and female gametes are produced.
2. Gametes meet during mating or pollination.
3. Nuclei of gametes fuse, creating a zygote.
4. The zygote divides and develops into an embryo.

 

 

Sexual Reproduction in Nature

Example	Gametes Involved	Fertilisation
Humans	Sperm (male) + Egg (female)	Internal fertilisation in the female body.
Plants	Pollen (male) + Ovule (female)	Pollination, followed by fertilisation inside the ovary.