Natural Selection and Selective Breeding 7th Grade Science

Natural Selection Natural Selection- a process by which organisms change over time as those with traits best suited to an environment pass their traits to the next generation.

Charles Darwin Scientist that observed and studied 13 species of finches on the Galapagos Islands. His main points Organisms produce more offspring than can survive. There is competition among offspring for food, space, and other resources.

Charles Darwin There is natural variety (difference) among the offspring of an organism. These variations are caused mainly by genetic differences. Individuals with certain traits are better suited to survive in their environment than those without the traits. Organisms that survive and reproduce pass the genes for their traits on to the next generation.

Natural Selection Natural selection is possible because of genetic variation among individual organisms within a population. Over generations, traits that enhance survival (i.e. are favorable in their environment) of a species are selected over those that do not. When all members of a population have the favorable trait, it is called an adaptation.

Natural Selection: Adaptations

Natural Selection Natural selection changes every species found on Earth. In the Galapagos Islands off the coast of Ecuador, the Galapagos Medium Ground Finch has developed a beak shape that is very different from other finches found in the same islands. Adaptations to the shape of a bird’s beak occur due to different food sources.

Darwin’s Finches

Natural Selection: The Peppered Moth When newly industrialized parts of Britain became polluted in the nineteenth century, smoke killed lichens growing on trees and blackened their bark. Pale colored moths which had been well camouflaged before when they rested on tree trunks became very conspicuous and were eaten by birds.

The Peppered Moth

Peppered Moth

Natural Selection: The Peppered Moth Rare dark moths, which had been conspicuous before, were now well camouflaged in the black background. As birds switched from eating mainly dark moths to mainly pale moths, the most common moth color changed from pale to dark. Natural selection had caused a change in the British moth population. The moths had adapted.

The Peppered Moth

Variation Variation- is a property of a population that occurs when individuals within a population differ in the characteristics.

Variation Variation can be observed by: External features- features are those traits that are easily observed. Behaviors- activities or actions that generally help an organism survive in its environment. Physiology- the study of the internal structures and functions of an organism.

Selective Breeding Selective Breeding- A form of artificial selection whereby deliberate breeding results in desired traits in plants and animals.

Dogs

Cats

Cattle

Pigeons

Teosinte and Corn

Chickens

Chicken Eggs

Apples

Selective Breeding Selective breeding of particular genes runs the risk of losing some of the other genes from the gene pool altogether, which is IRREVERSIBLE. This is INBREEDING DEPRESSION, where the exclusivity of the advantageous genes means that some other less desirable genes are phased out. Genetic diversity in the long term is reduced, because many organisms end up with similar genetic material due breeding with each other constantly.

Problems with Selective Breeding Bloodhounds develop loose skin around their eyes, increasing the potential unwanted small objects getting stuck in their eyes.

Problems with Selective Breeding Centuries of selective breeding has led to the creation of many different breeds of animal all inheriting very similar characteristics to the previous generation, which may include genetic diseases. (Many King Charles Cavaliers develop heart murmurs and other heart problems, cruelly cutting their lives short)

Problems with Selective Breeding Bulldogs develop oversized heads which result in many having to be born through caesarean section. Pekingese dogs have very short faces, making it hard for them to breathe or smell.

Labrador Retrievers Retrieve birds for hunters Sniff out drugs Sniff out bombs Sniff out people buried under rubble Sniff out deer antlers to use to make knife handles Seeing eye dogs Therapy dogs

Closing Task Create your own definition of natural selection. 1 COMPLETE SENTENCE Be prepared to share.

FRIDAY Engage: What are adaptations? Scholastic Study Jams: http://studyjams.scholastic.com/studyjams/jams/science/animals/animal-adaptations.htm

The Arctic Hare