Natural Selection & Gene Flow

Directional Selection

favors one extreme phenotype

Stabilizing selection

favors the intermediate phenotype

Disruptive selection

favors extreme phenotypes

Balancing selection

no single allele has a distinct advantage

Balancing selection has _____ advantage and _____ dependent selection

heterozygous, frequency

Directional selection ____ genetic variation

decreases

Stabilizing selection ____ genetic variation

decreases

Disruptive selection ____ genetic variation

increases

Balancing selection ____ genetic variation

maintains

Gene flow

the movement of alleles between populations

Gene flow causes allele frequencies in the two populations to be more ____

alike

Genetic drift

the change in allele frequencies in a population due to random chance

Genetic drift especially affects _____ populations

small

Founder effect

a change in allele frequencies when a new population is established from a small population immigrating to a new geographic area

Bottleneck effect

when a large population experiences a sudden reduction in size

The average depth of the beak in ground finches on one of the Galápagos Islands increased over the years. This change is thought to be correlated with availability of larger seeds only, due to a drought. What type of selection might have affected the beak depth in the ground finch?

directional

Toucans disperse seeds of key forest species such as juçara palms by eating the fruit and defecating the seeds in new locations, sometimes more than a kilometer away. 

If there are no toucans, is the genetic diversity of palms likely to increase or decrease within forests (and why)?

Decrease (due to decrease in gene flow)

In a​ bell-shaped curve, the x​-axis ​(horizontal direction) of the graph represents which of the​ following?

The value of a particular​ characteristic; characteristics of an organism can include such traits as size and color.

True or​ false? Heterozygote advantage refers to the tendency for heterozygous individuals to have better fitness than homozygous individuals. This higher fitness results in less genetic variation in the population

False

Long necks make it easier for giraffes to reach leaves high on​ trees, while also making them better fighters in​ "neck wrestling" contests. In both​ cases, which kind of selection appears to have made giraffes the​ long-necked creatures they are​ today?

Directional selection

Women often have complications during labor while giving birth to very large​ babies, whereas very small babies tend to be underdeveloped. Which kind of selection is most likely at work regarding the birth weight of​ babies?

Stabilizing selection

​Black-bellied seedcrackers have either small beaks​ (better for eating soft​ seeds) or large beaks​ (better for hard​ seeds). There are no seeds of intermediate​ hardness; therefore, which kind of selection acts on beak size in​ seedcrackers?

Disruptive selection

Small Aristelliger lizards have difficulty defending​ territories, but large lizards are more likely to be preyed upon by owls. Which kind of selection acts on the adult body size of these​ lizards?

Stabilizing selection

What is one main difference between Natural Selection and Genetic Drift?

Genetic drift is random and natural selection is not