Looking at the “natural” population below: Long neck Short neck

Looking at the “natural” population below:


Long neck

Long neck Short neck


Which will eat?

Which will live?

Which will have kids?

Long neck

Long neck Short neck

1.Will the population be exactly the same the next year?

2. What determines neck length?

3. Can the individual giraffes change their DNA if they want to/try? Explain

4. What process is being demonstrated here?

no

DNA

No, can’t change their DNA

Natural Selection/ Survival of the Fittest

True/False

5. Giraffes got long necks by stretching for leaves.

6. An individual organism (a giraffe) can change if it wants to.

7. Individuals adapt to their environment and pass the adaptations on to their offspring.

8. Individuals evolve.Populations

Natural Selection

1.Variation

L = long neck, l = short neck(simplified- may be polygenic – multiple

genes): LL, Ll, ll gene pool – all alleles (genes) in the population

2. Struggle to Survive LL, Ll, ll

3. Most fit survive and reproduce LL x Ll offspring: LL or Ll

Can cause a population to change

What Causes Evolution?

1. NATURAL SELECTION – organisms with the best FIT to the environment survive and reproduce.

2. GENETIC DRIFT -

a. Bottleneck

b. Founder Effect

Change in the gene pool of a small population due to chance



2. GENETIC DRIFT -

Bottleneck

Founder Effect

Change in the gene pool of a small population due to chance

2. GENETIC DRIFT - Change in the gene pool of a small population due to chance.

Gene pool – all the genes in a population at any one time. Each person has two alleles for each trait.

a. Genetic Bottleneck • Occurs when

species numbers are low

• Results in little genetic variety

• Everyone has very similar genes in population

2. GENETIC DRIFT - Change in the gene pool of a small population due to chance.

a. Genetic Bottleneck - something (disaster) reduces population size, killing randomly (unselectively). Survivors genetic make up unlike original population.

Elephant seal pop. 1890 = 20 (due to extensive hunting), now = 30,000.

Problem: very little genetic variation.

Genetic bottlenecks are often caused by human activities

• At the low point in their population, California sea otters . have numbered a few dozen.

• Since 1972, after their Marine Mammal Protection, how much genetic variation could have occurred?

The Story of Cheetahs

Figure 13.22

Approximately 10,000 years ago, at the end of a time called the Pleistocene Epoch also known as the Great Ice Age (a geographical time period from approximately 2 million to 10,000 years ago), the world's environment underwent drastic changes in climate.

Over a few thousand years, 75 percent of the mammal species in North America, and Europe died.When mammals began to die, so did all the cheetahs in North America and Europe and most of those in Asia and Africa.

Cheetahs may have migrated to more suitable environment as ice covered a large part of the northern hemisphere and sea levels fell.

The Story of Cheetahs (continued)

The cheetah survived the mass extinction of the Pleistocene Epoch, but its numbers were greatly reduced. Brothers were left to reproduce with sisters and parents with siblings, which led to the founding of the next generation, and inbreeding took place.

This occurrence - a severe reduction in population - is called a "bottleneck." Every cheetah alive today appears to be so inbred that genetically they are as closely related as twins (two offspring, or individuals born at the same birth).



2. GENETIC DRIFT -

a. Bottleneck

b. Founder Effect - few individuals colonize isolated area, island/ lake. Genetic make up unlike original population. Have limited genetic diversity. Accounts for high frequency of inherited disorders in populations.


1. NATURAL SELECTION

2. GENETIC DRIFT -

a. Bottleneck

b. Founder Effect

3. MUTATIONS – Changes in an organism’s DNA. Very rare. Original source of genetic variation. Raw material for natural selection.

4. MIGRATION

Patterns of Evolution

Geographic history of Earth helps explain the current distribution of species.

Shifting continents = mass extinctions (Pangaea), climate change, habitat destruction, change in ocean currents, adaptive radiations, isolation, volcanoes, earthquakes etc

Currently North America and Europe are drifting apart by 2 cm per year.

Continental Drift

Divergent Evolution

Organisms become so different they can no longer interbreed and become a new species

New Species share common ancestor

Species A

Ancestral Species

Species B

Evolution & Speciation

Species A

Species B

Species C

Species A is separated into 2 isolated populations, each affected by different environmental conditions

Divergent evolution is the basis of new species creation

• It requires reproductive isolation or geographic isolation of the new group from the old.

• New traits forms based on the demands of the new environment

Adaptive Radiation

• When several species evolve from an ancestor each to fill a different niche of the environment

HoneyCreepers - Hawaii

Convergent Evolution

Convergent Evolution

• When groups that are NOT closely related both change in the same direction due to similar environmental pressures

• Species A

Similar Structures

Species B

Convergent evolution of unrelated species in similar environments

• Cactus is a New World plant (Americas)

• Euphorbia is an old world (African) plant

• Both adapted to desert conditions of heat and dry climates

• What traits do both plants share in common?

15. Analyzing Graphs The following graph shows drug resistance that develops over time in the virus that causes AIDS. Use the graph to answer the questions below.

a. What trend appears in all the patients by the end of the third week?b. Explain what happened to the virus population over the ten weeks of exposure to the drug.c. How do these data reflect a problem in treating patients with the virus?

Documents

Looking at the “natural” population below: Long neck Short neck