Lesson 3 Essay Questions: 1. Compare and contrast directional selection and disruptive selection and provide an example of each.

Both directional and disruptive selection is a type of natural selection. Natural selection is the differential survival and/or reproduction of organisms as a function of their physical attributes. (phenotype) This results in evolution over many generations. Each mode of selection alters the mean or variance of a phenotypic trait in a population or species. These distributions can be represented in bell curves. Both selection processes can be influenced by human interaction.

Directional Selection occurs when an extreme phenotype at one end of a population distribution is favored over all other phenotypes and over many generations it will lead to one distinct form.
An example of directional selection is resistance to antibiotics. When an antibiotic is administered a few of the bacteria survive because they are genetically resistant. The surviving bacteria will pass on this phenotype (resistance) to the next generation. Over time the bacteria will be completely resistant to the initial antibiotic.

Disruptive selection is an outcome of natural selection in which both extreme phenotypes at the end of a population distribution are favored over the average phenotype. This type of selection favors polymorphism, the occurrence of two different forms in a population of the same species. It can also lead to specification and form two or more different species in areas of drastic environmental changes. Disruptive selection is the rarest form of the three types of natural selection. Environmental pollution can drive disruptive selection to choose different coloring in animals/insects for survival. As in one of the most studied examples of disruptive selection - London’s Peppered Moths. It was noted that most of the moths found in rural areas were almost always a light color. These same moths in industrial areas tended to be a darker color. Very few medium colored moths were seen at either location. The darker colored moths blended in better to the polluted area and survived better from predators. The reverse was true in the rural areas. The medium colored moths stood out in both environments making them easier prey, therefore very few of them survived after disruptive selection.

2. Many pathogenic bacteria species are becoming resistant to antibiotics. Explain how such adaptations can develop through the process of natural selection?
When an existing population of bacteria is introduced to an antibiotic, natural selection starts. The beginning population of bacteria have different characteristics/traits. When the antibiotic is given some of the bacteria will survive due to these different characteristics/traits. The bacteria that survive have these traits. The surviving bacteria reproduce. They pass on the surviving traits. Each generation that passes will weed out the nonessential traits and keep the survival traits. Each generation produce more offspring then will actually survive, thus refining the survival traits. Over time the bacteria will evolve into a new super bacteria. This process will occur every time a new antibiotic is introduced. The only difference is the amount of time it takes to get to the new super bacteria. 3. What are the major evolutionary trends that developed among major vertebrate groups, specifically those that allowed for the transition from aquatic to terrestrial life?

Vertebrate evolution is most often thought of as going from water to land, Once on land they continue to evolve to occupy diverse habitats. Vertebrates are actually a sub phylum with in the phylum Chordata. Chordates have four characteristics. A dorsal supporting rod called a notochord, a dorsal tubular nerve cord, pharyngeal pouches, and a tail. As embryos, vertebrates have these four characteristics.
Fishes were considered the first vertebrates. Today there are three living classes of fish, Jawless fishes, Cartilaginous fishes, and Bony fishes. Fishes with endoskeletons of cartilage and some bone in their scales were the first to have jaws. Jaws are believed to evolved from the first pair of gill arches. The presence of jaws permits a predatory lifestyle. Early bony fishes or lobed finned fishes had lungs.
Amphibians were the first group to have jointed appendages and to invade land. Amphibian means living both on land and in water. Besides the jointed limbs they have other features that are not seen in the fishes. Eyelids that keep the eye moist, sound producing larynx, and ears adapted to pick up sound waves. Amphibians have a great variety of reproductive strategies. This variety as well as the adaptations noted above made them successful colonizers of the land environment.
Reptile are the next step in the evolutionary tree of chordates. The most outstanding adaptation of reptiles is that they have a means of reproduction suitable to a land existence, Fertilization is internal and the female lays leathery , flexible shelled eggs. The amniotic egg made development on land possible and eliminated the need for a water environment during development.
Birds are considered feathered reptiles. They share a common ancestor with the crocodile. Nearly every anatomical feature of a bird can be related to its ability to fly. Birds lay a hard shelled amniotic egg rather than the leathery egg of other reptiles.
Mammals are amniotes as well and share a common ancestor with the reptiles. However they represent a different evolutionary lineage from the reptile lineage that led to birds, Some of the earliest mammalian groups are still represented by the monotremes (mammals like bird that have a cloaca, they also lay hard shelled amniote eggs spiny anteater and duck billed platypus) and marsupials (young develop inside the females body, born in a very immature condition, crawl into a pouch on t he mother abdomen where it attaches to a nipple on the mammary glands and continues to develop. Opossum, koala bear, kangaroo)). The two chief characteristics of mammals are hair and milk producing mammary glands. All mammals are endoderms and generate internal heat, Many of their adaptations are related to temperature control.

4. Providing examples, explain how sexual reproduction in plants has evolved to become less dependent on water?

There are 5 specific events is the evolution of land plants.
Protection of the embryo.
Evolution of vascular tissue.
Evolution of leaves (microphylls and megaphylls)
Evolution of seeds.
Evolution of flowers.

All of these changes have helped plants become less dependent on water. Seed bearing vascular plants, gymnosperms and angiosperms have adapted tissue structures for life in dryer climates. They produce seeds, a seed contains an embryo and stored organic nutrients within a protective coat. A seed plant produces two types of microscopic gametophytes, a male and female gametophyte. The male is the pollen grain and produces sperm. The female is the ovule. The process of pollination occurs when the pollen lands on the female reproductive structure. Once there, the pollen will grow a pollen tube and the sperm migrates toward the egg. This alleviates the sperms need for water to swim to the egg.

Gymnosperm means naked seed. In these plants ovules and seeds are exposed to the surface of a cone scale (modified leaf). Pollination of these types of plants is mostly done by the wind dispersal of the dry pollen grains. This group of plants include Conifers, Cycads and ginkgo.

Angiosperm means covered seeds. Flowers are the reproductive structure found in angiosperms. The produce seeds enclosed by fruit, Most flowers have certain parts in common. No matter what plant they are on. Flowers also have both male and female reproductive structures . The male part is called a stamen. The stamen has a stalk called a filament and an anther where pollen is produced. In most flowers the anther is positioned in such a way that the pollen can be carried away by the wind or a pollinator. The female part is the carpel. The carpel has three sections. The swollen base is called the ovary and holds from 1 to hundreds of ovules. The style elevates the third part, the stigma which is sticky and adapted for the collection of pollen grains. By the ovary there ae glands that produce nectar. This nectar is a nutrient that is gathered by the pollinators as they go from flower to flower. Most angiosperms coevolved with pollinators such as bees and other insects. These pollinators allow the pollen grains from one plant to reach the reproductive parts of another plant at another location.
Once pollination occurs, it will germinate.
The pollen tube carries two sperm into a small opening in the ovule. This alleviates the sperms need for water to swin to the egg, as in the above mentioned example.
During double fertilization one sperm comes together with and egg nucleus forming a diploid zygote and the other sperm form with other nuclei forming a triploid or endosperm. In angiosperm the endosperm is stored food.