Understanding Variation in Nature

This page delves into the causes of variation among organisms, focusing on genetic and environmental factors.

Genetic Variation Genetic variation arises from the inheritance of genes from parents. This explains why individuals look different, with less variation between family members than in the general population.

Example: Eye color, nose shape, and sex are determined by genetic information inherited from parents.

Environmental Variation Environmental factors also contribute to differences between individuals of the same species.

Example: Scars are a form of environmental variation.

Combined Causes of Variation Many characteristics are influenced by both genetic and environmental factors.

Example: Height and weight are affected by both genes and environment, such as the genetic tendency to be overweight.

Investigating Variation Scientists use various methods to study variation:

• Growing genetically identical plants in different conditions
• Studying groups of genetically similar animals
• Observing identical twins

Highlight: Studying identical twins separated by adoption provides insights into the relative influences of genetics and environment on human traits.

Evolution by Natural Selection This section introduces the concept of natural selection:

• Organisms compete within their species
• Those with advantageous traits are more likely to survive and reproduce

Mutation and Genetic Variation Mutations are changes in the DNA code that can introduce new variants into a species' gene pool.

Vocabulary: Phenotype - the observable characteristics of an organism resulting from the interaction of its genotype with the environment.

Highlight: While many mutations have no effect or are harmful, some can produce adaptations that make an organism better suited to its environment.

Selective Breeding

This page discusses the process of selective breeding and its implications.

Definition of Selective Breeding Selective breeding involves choosing desired characteristics and breeding animals or plants with these traits to produce offspring with enhanced desired characteristics.

Process of Selective Breeding:

1. Select organisms with desirable traits from a mixed population
2. Use these organisms as breeding stock
3. Select offspring with desired characteristics for further breeding
4. Continue this process over many generations

Example: Selective breeding is used to develop disease resistance, increase meat or milk production, and alter colors in plants and animals.

Results of Selective Breeding Centuries of selective breeding have led to dramatic changes in domesticated plants and animals, resulting in organisms with combinations of genes that wouldn't occur naturally.

Limitations of Selective Breeding While selective breeding has been responsible for significant agricultural progress, it has drawbacks:

• Reduces the number of alleles in a population
• Decreases variation between individuals
• Can make populations vulnerable to environmental changes due to lack of genetic diversity

Vocabulary: Alleles - alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

Highlight: The reduction in genetic variation caused by selective breeding can be problematic when environmental conditions change, as the lack of diversity may mean no individuals in the population can cope with the new conditions.