Cloning and Selective Breeding

Question

Dolly the sheep was the first mammal cloned from a somatic cell (any body cell that is not a sperm or egg cell). This was done by removing the nucleus of an egg cell and replacing it with the nucleus of a somatic cell from the mammary gland of another sheep. The donor of the egg cell had a black face, while the donor of the somatic cell had a white face. Since Dolly had a white face, it was assumed that Dolly had the genetic makeup of the somatic cell donor. DNA testing verified that Dolly was, indeed, of the same genetic makeup as the somatic cell donor. Dolly had the identical genetic makeup of the somatic donor and did not share any genetics of the egg donor.

Another way that humans have been able to manipulate the characteristics of organisms is through artificial selection (selective breeding). Through selective breeding, different dog breeds are created with desired characteristics. One such dog is the English bulldog. Over the years, this animal has been bred to be larger and to appear more intimidating. However, because of the excess in selective breeding over many generations, today’s English bulldogs can suffer from a variety of health problems. In general, they have a high incidence of cancer, skin problems, arthritis, and will likely have a short life span.

Constructed Response Question
Does selective breeding increase or decrease the diversity of a species over time? Provide an explanation.

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Answer 1

Selective breeding generally decreases the genetic diversity of a species over time. This process involves choosing specific individuals with desired traits to reproduce, which often leads to breeding within a narrow gene pool. As a result, the frequency of certain alleles may increase while others diminish or disappear entirely.

For example, in the case of the English bulldog mentioned in the prompt, selective breeding has resulted in a breed with specific physical characteristics, such as a characteristic flat face and stocky build. While these traits may be desirable for aesthetic or functional reasons, the limited genetic diversity that emerges from such focused breeding practices can predispose the breed to a range of health problems. This reduction in genetic variety can reduce the population's ability to adapt to environmental changes or resist diseases, making the population more vulnerable in the long run.

In summary, while selective breeding may achieve specific desired traits, it tends to narrow the genetic diversity within a species, leading to potential long-term risks for the health and resilience of the population.