.

TOR

If

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propose aging is programmed

Hydra

Hydra

Hydra

Figure 2)

Figure 2

Hydra

can't

([link]

After speciation,

Summary

Polyploidy is a condition in which a cell or organism has an extra set, or sets, of chromosomes. Scientists have identified two main types of polyploidy that can lead to reproductive isolation of an individual in the polyploidy state. Reproductive isolation is the inability to interbreed. In some cases, a polyploid individual will have two or more complete sets of chromosomes from its own species in a condition called autopolyploidy (Figure 6.5.76.5.7\PageIndex{7}). The prefix “auto-” means “self,” so the term means multiple chromosomes from one’s own species. Polyploidy results from an error in meiosis in which all of the chromosomes move into one cell instead of separating.

Scientists have documented numerous cases of allopatric speciation taking place. For example, along the west coast of the United States, two separate sub-species of spotted owls exist. The northern spotted owl has genetic and phenotypic differences from its close relative: the Mexican spotted owl, which lives in the south (Figure 6.5.46.5.4\PageIndex{4}).

that interbreed

Link to discussion of self-incompatibility in plants.

064

The Hardy-Weinberg principle assumes conditions with no mutations, migration, emigration, or selective pressure for or against genotype, plus an infinite population; while no population can satisfy those conditions, the principle offers a useful model against which to compare real population changes.

, is called the founder effect. Natural selection, random drift, and founder effect

soil)

Some

disease

Culex quinquefasciatus

16.4.1

) H

: 16.5

Here x is the size of the population at a given time, r is inherent per-capita growth rate, and K is the carrying capacity. At low population densities, x(t) is much smaller than K and so the main determinant for population growth is just the per capita growth rate. However, as N(t) a

by fighting for scarce resources.

he thre

parts of this article.

need not

parthenogenesis

This 50% cost is a fitness

t as every young organism created can bear its own young.

secondary sexual characteristics that do not benefit the individual’s likelihood of surviva

The result of this type of selection is increased genetic variance as the population becomes more diverse.

migration

in a population

​​​​​Processes and Patterns of Evolution

Pangaea (about 200 million years ago) are distributed worldwide. Groups that evolved since the breakup appear uniquely in regions of the planet, such as the unique flora and fauna of northern continents that formed from the supercontinent Laurasia and of the southern continents that formed from the supercontinent Gondwana. The presence of members of the plant family Proteaceae in Australia, southern Africa, and South America is best by their presence prior to the southern supercontinent Gondwana breaking up

Other

18.1.6

Figure 18.1.5)

Equus ferus

Equus

Echinacea purpurea

Liatrus spicata

Sexual reproduction also leads to genetic diversity: when two parents reproduce, unique combinations of alleles assemble to produce the unique genotypes and thus phenotypes in each of the offspring

fitness

Scientists still do no know how these cold-blood animals are able to move in the cold (10 to 15°C) temperatures of the Andean night

Potamites montanicola

Carnegiea gigantea