Strategies In Animals Inbred Lines And Selective Breeding

In animal studies there are two fundamental strategies to determine whether a trait is under the influence of genetic variation. The first one is the comparison of inbred strains. An inbred strain is generated by repeatedly mating close relatives. Since these relatives (usually brothers and sisters) are approximately 50% genetically alike (counting only those genes for which their parents had different genotypes), individuals of the same sex will be almost genetically identical after 20 generations of inbreeding. Within an inbred strain, nearly all trait variability will be caused by the environment, whereas differences among strains will be virtually genetic in origin. Therefore, when in a controlled testing environment multiple strains are compared for a specific behavior, the extent to which inter-strain differences exceed the pooled within-strain variability provides a test of the existence of genetic influence. A good illustration of the variation in inbred strains is the data collected on aggressive behavior in the laboratory of Pierre Roubertoux in Orleans, France (Table I). As can be observed in the table, levels of aggressiveness vary enormously among strains. NZB mice always attack (20 of 20 animals; 100%), whereas C57BL/6J males almost never attack (1 of 20; 5%).

Inbred strains are generally stable over time and across laboratories. For instance, NZB mice have been demonstrated to be aggressive in several laboratories on different continents since they were first tested. However, certainly the most important advantage of inbred strains is that they are the conditio sine qua non for the recently developed high-tech molecular-genetic techniques, such as the creation of knockouts and transgenics. A disadvantage of the use of inbred strains is that they do not represent natural populations in which heterozygosity is the rule rather than an exception.

Another useful technique to show that a specific trait is genetically influenced is selective breeding or artificial selection. This method has been used throughout recorded history, even long before people understood how it actually worked, and is currently still being applied extensively. It is based on the fact that the offspring of animals with a desired quality are more likely to demonstrate that quality than the progeny of random individuals. For centuries, farm animals and pets have been bred for desired characteristics, some of them behavioral (e.g., in dogs: hunting dogs, shepherd

Table I

Proportion of Attacking Males in Seven Inbred Mouse Strains

Table I

Proportion of Attacking Males in Seven Inbred Mouse Strains

Strain

% attacking males (N=20)

Understanding And Treating Autism

Understanding And Treating Autism

Whenever a doctor informs the parents that their child is suffering with Autism, the first & foremost question that is thrown over him is - How did it happen? How did my child get this disease? Well, there is no definite answer to what are the exact causes of Autism.

Get My Free Ebook


Post a comment