Genes, inheritance and selection Study Guide

Reproduction is a fundamental biological process by which new individual organisms are produced. There are two main types: asexual and sexual reproduction, each with distinct advantages and disadvantages that influence an organism's survival and evolution. Asexual reproduction involves a single parent producing genetically identical offspring, commonly seen in organisms like bacteria, some plants, and certain animals (e.g., starfish regeneration). A key advantage is its speed and efficiency, allowing rapid colonisation of stable environments without the need to find a mate. All desirable traits are passed directly to offspring. However, the lack of genetic variation means that a sudden change in the environment, such as a new disease or climate shift, could wipe out an entire population because no individual has a unique genetic makeup to offer resistance.

Sexual reproduction, conversely, involves two parents contributing genetic material to produce offspring that are genetically diverse. This usually involves the fusion of male and female gametes. Most animals and many plants reproduce sexually. The primary advantage of sexual reproduction is the genetic variation it introduces into a population, which enhances the species' ability to adapt to changing environments. If a new disease emerges, some individuals in the population may have resistance due to their unique genetic combination, increasing the chance of survival for the species. The disadvantage is that it is often a slower process, requiring more energy to find a mate, court, and reproduce, making it less efficient in rapidly colonising new areas. Also, only half of an individual's genes are passed on to each offspring, which can be a disadvantage if the parent possesses highly beneficial genes that might be 'diluted' or combined with less advantageous ones. Understanding these trade-offs helps explain the prevalence of each reproductive strategy in different ecosystems.

Evolution describes the process by which the inherited characteristics of a population of organisms change over successive generations. This fundamental biological concept explains the diversity of life on Earth. The primary mechanism driving evolution is natural selection. Natural selection occurs because individuals within a population have variations in their traits, some of which are inherited. In any given environment, resources are often limited, leading to competition. Individuals with inherited characteristics that make them better adapted to their environment are more likely to survive and reproduce. These successful individuals then pass on their advantageous traits to their offspring. Over many generations, these advantageous traits become more common in the population, while less advantageous traits become less common or disappear. This gradual shift in the genetic makeup of a population is evolution. If this process continues over a very long time, and populations become reproductively isolated (meaning they can no longer interbreed), it can lead to the formation of entirely new species, a process called speciation. Evolution is not about individual organisms changing during their lifetime, but rather about changes in the proportion of different characteristics within a population over many generations.