Reproduction

Sexual Reproduction

Sexual reproduction is where genetic information from a mother and father is mixed together to form genetically different offspring. Each offspring will inherit different genes from their parents, giving them all different features and characteristics.

Genetic information from the mother and father is carried in sex cells called gametes which are formed in a process called meiosis. When the nuclei of the two gametes fuse together in fertilisation they form a zygote.

• Gametes in animals are called sperm cells (from father) and egg cells (from mother).
• Gametes in flowering plants are called pollen (from father) and egg cells (from mother).

Humans have 46 chromosomes and their gametes (sperm and egg cells) have 23 chromosomes. This is because when the nuclei of the gametes fuse, the genetic information combines together giving the offspring a full set of chromosomes.

Asexual Reproduction

Asexual reproduction is where offspring are created from one parent only. As there is no fusion of gametes or mixing of genetic information, offspring will be genetically identical to each other and their parent (clones).

This usually happens through mitosis, where a cell makes a copy of its genetic information and then splits into two. 

Bacteria and some plants and animals reproduce asexually. 

Sexual vs Asexual Reproduction

Humans often take advantage of natural selection and use selective breeding to increase food production. Animals with desirable traits (those who produce more milk or meat) are bred together to create offspring with these traits and produce more food.

Organisms that Reproduce Sexually and Asexually

Some organisms reproduce sexually and asexually, which method they use at a given time depends on certain circumstances.

Some examples include:

• Malarial parasites cause the disease malaria. Mosquitos act as a vector; they carry the parasite and spread the disease to humans by biting them. The parasite reproduces sexually when it is in the mosquito vector but reproduces asexually in the human host. 
• Fungi release spores that grow into new fungi if they land on a suitable surface. The spores are either produced sexually or asexually. The majority of the time they release asexual spores that produce offspring that are identical to the parent. However, sometimes they produce spores produced by sexual reproduction to introduce some variation to the population, particularly when conditions are unfavourable. 
• Strawberry Plants reproduce sexually, by producing gametes in their flowers but can also reproduce asexually by producing runners. Runners are stems that grow horizontally from the plant and new plants that are genetically identical to the parent grow at various points along them. 
• Daffodils reproduce sexually using gametes found in their flowers but can also reproduce asexually from their bulbs. Daffodil bulbs can form new bulbs that divide off and grow into new plants.