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Diversity and Variation

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Diversity and Variation
Chapter 18 Outline: Diversity and Variation

18.1 The Species Concept

TAXONOMY- classifying organisms in ways that reflect relationships and help distinguish one type of organism from another.

SPECIES- group of organisms that is capable of breeding offspring, or mating, with another in nature to produce fertile offspring.

Individual members of a species may look very different from eachother.

Such differences among members of a species are known as variations

Natural selection acts on variation, resulting in changes in species or the evolution of new species

Figure 18.1- five breeds of dogs

Figure 18.2 geographic variation in the human species

Variations in a population- polymorphism, geographic variation, and individual variation

Figure 18.3- individual variation in a human population and in a sheep population

Members of related species may interbreed occasionally

Species is a population of individuals that breed and produce fertile offspring under natural conditions

Figure 18.4- two species of canines

Figure 18.5- two species of bears

18.2 Classification and homologies

Classification is important for both practical and scientific reasons.

Taxonomy plays a role in public health, ecology, key for understanding the unity of life

Figure 18.6- species that come in contact but do not interbreed

Figure 18.7- the male Krause with her two colts

Taxonomists use structure, biochemistry, behavior and genes to classify organisms

Classification focuses on structures that indicate a related evolutionary ancestry

These structural resemblances = homologies

Structures that are similar in appearance and function but are not the result of shared ancestry = analogies

Chemical homologies are also evidence of close evolutionary relationships

Figure 18.8- one way of classifying organisms

Table 18.1 nucleotide sequence of part of a gene in all apes and monkeys

Table 18.2 percent differences among

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