Genetic Variation and Selective Breeding

Genetic Variation

• Definition: Genetic variation refers to the differences in genetic information among individuals within a population.

  • Source: Mutations are the primary source of genetic variation; they are permanent changes in the DNA sequence.

Types of Mutations

• Neutral Mutations:

  • Effect: Provide neither benefit nor harm to the organism.

• Harmful Mutations:

  • Effect: Decrease reproductive success.

  • Example: Huntington’s disease.

• Beneficial Mutations:

  • Effect: Improve an organism's chance of survival and reproduction.

  • Example: Sickle-cell allele carriers have increased resistance to malaria.

Visibility of Mutations

• Observation: Some mutations are easily seen while others may not be visible but still affect the organism.

Selective Breeding

• Definition: The process of domestication alters species qualities to match human needs.

• Method: Conducted through captive breeding or artificial selection.

• Example:

  • The domestication of wolves into modern dogs illustrates artificial selection, where traits are selected for usefulness or appearance.

  • A mutation that causes dwarfism led to breeds like basset hounds and dachshunds.

Case Studies on Domestication

• Silver Fox Experiment: Conducted by Dmitry Belyaev to study domestication traits using foxes.

• Tomato Domestication:

  • Tomato plants show significant variability in size, fruit production, and taste.

  • Farmers selectively bred the best-performing seeds over multiple seasons to produce desired traits.

Consequences of Artificial Selection

• Benefits: Creation of desirable traits for agriculture and domestic animals.

• Drawbacks: Reduces genetic diversity, which can lead to vulnerability in populations.

  • Examples:

  • Large corn cobs may attract pests.

  • Certain dog breeds may exhibit higher susceptibility to diseases, such as cancer.

Limitations of Artificial Selection

• Key Principle: Artificial selection cannot generate entirely new traits; it can only select from existing variations.

• Mutation Role: New traits arise only through new mutations, while beneficial or neutral mutations persist across generations, and harmful or unattractive mutations are typically eliminated.

Connection to Evolution

• Inquiry: If we can transform a population of wolves into diverse dog breeds over a few thousand years through artificial selection, what changes could occur naturally in species over millions of years?

Homework Assignment

• Read pages 282-287.

• Answer questions 1-4 on page 287.