Topic 17: Variation & Selection

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What is variation?

The differences between individuals of the same species.

What does continuous variation result in?

A range of phenotypes between two extremes; examples include body length and body mass.

What does discontinuous variation result in?

A limited number of phenotypes with no intermediates; examples include ABO blood groups, seed shape in peas and seed color in peas.

Discontinuous variation is usually caused by…?

Only genes.

Continuous variation is usually caused by…?

Both genes & the environment.

What is mutation?

Genetic change

Mutation is the way in…?

Which new alleles are formed.

What increase the rate of mutation?

Ionising radiation & some chemicals.

What is genetic mutation?

A random change in the base sequence of DNA.

What are the sources of genetic variation in populations?

Mutation, meiosis, random mating, random fertilization.

What is an an adaptive feature?

An inherited feature that helps an organism to survive and reproduce in its environment.

What are the adaptive features of hydrophytes to their environments?

The plants are adapted to live in extremely wet conditions having features such as:

1. Large air spaces in their leaves for flotation, keeping the leaves close to the water surface where there is more light for photosynthesis.

2. Small roots so they can extract nutrients from the surrounding water through their tissues.

3. Stomata is usually open all the time and mainly found on the upper epidermis of the leaf so it can exchange gases much more easily with the air.

What are the adaptive features of xerophytes to their environments?

The plants are adapted to live in extremely dry conditions having features such as:

1. Thick waxy cuticle - the cuticle cuts down water loss in two ways: it acts as a barrier to evaporation and the shiny surface reflects heat and lowers the temperature as a result.

2. Sunken stomata - stomata may be sunk in pits in the epidermis; moist air trapped here lengthens the diffusion pathway and reduces the evaporation rate.

3. Small leaves: many xerophytic plants have small, needle-shaped leaves which reduces the surface area and therefore the evaporating surface.

4. Extensive shallow roots - Allows for quick absorption of large quantities of water when it rains.

5. Thickened leaves or stems - Contain cells that store water.

What is natural selection?

When the individuals that have the best adaptive features are the ones most likely to survive and reproduce in any environment. Natural selection occurs because individuals in a population show genetic variation caused by differences in their alleles. Organisms produce more offspring than the environment can support, which leads to competition for resources such as food and space, resulting in a struggle for survival. Individuals with characteristics that are better adapted to the environment are more likely to survive and reproduce. As a result, these individuals pass on the alleles responsible for these advantageous characteristics to their offspring. Over time, these alleles become more common in the population, leading to a greater number of individuals with the better-adapted characteristics in the next generation.

What is adaptation?

The process, resulting from natural selection, by which populations become more suited to their environment over many generations.

What is an example of natural selection?

The development of strains of antibiotic resistant bacteria.

What is selective breeding?

A process in which humans select individuals with desirable characteristics and breed them together. These selected individuals are crossed to produce offspring for the next generation. Not all offspring will show the desired characteristics, so those that do are selected and bred together again. This process is repeated over many successive generations until the desired characteristics are consistently shown in the offspring, producing a new breed.

How has selective breeding by artificial selection improved crop plants?

Selective breeding in plants is carried out by humans choosing plants with desirable characteristics and breeding them together over many generations. Crop plants are selectively bred for features such as disease resistance, increased yield, tolerance to harsh weather conditions such as drought, improved taste, and large or unusual flowers.

How has selective breeding by artificial selection improved domesticated animals?

What are the differences between natural and artificial selection?

1. Natural selection occurs naturally while artificial selection happens only when humans intervene.

2. Natural selection results in the development of populations with features that are better adapted to their environment and survival while Artificial selection results in development of populations with features that are useful to humans and less to the survival of the indivindual.

3. Natural selection usually takes a long time to occur while Artificial selection takes less time as only individuals with the desired features are allowed to reproduce.