Bi 101 (Fall 2006)                How Organisms Evolve                            Dr. Dutton

 

Populations, Genes, & Evolution

 

Important Terminology

Allele: one of several alternative forms of a particular gene

Genotype: the genetic composition of an organism; the actual alleles of each gene carried by an organism

Phenotype: the physical characteristics of an organism; can be defined as outward appearance (e.g. flower color), as behavior, or in molecular terms (e.g., glycoproteins on red blood cells)

 

Evolution is a property of _________________________ - NOT individual organisms

 

 

All the _________________________ (functional segments of DNA located at particular places on chromosomes) in a population make up the

 

 

 _________________________ _________________________

 

 

     The relative frequencies of various _________________________ (alternative forms

 

 

of genes) in a population are the _________________________

 

 

_________________________

Changes in allele frequencies that occur in a gene pool over time is …

 

 

_________________________

 

The Hardy-Weinberg Principle

States: that under certain conditions, allele and genotype (the actual alleles of each gene carried by an organism) frequencies in a population will remain constant over time (I.e., evolution will not occur)

 

 

An _________________________ _________________________ is a hypothetical population in which evolution does NOT occur

Such an evolution-free population is an equilibrium population that will remain in

 

 

_________________________ _________________________ as long as:

 

Conditions for Hardy-Weinberg

 

 

1.  There is _________________________ _________________________

 

 

2.  There is _________________________ _________________________

 

 

_________________________ (migration) between populations

 

 

3.  The population is _________________________ _________________________

 

4. 

 

 

 

5.      There is _________________________ _________________________

 

 

_________________________ (all genotypes reproduce equally well)

 

How Many Natural Populations are in Genetic Equilibrium?

 

 

_________________________ _________________________!

 

So why use Hardy-Weinberg?

 

Provides a useful starting point for studying the mechanisms of Evolution

 

What Causes Evolution?

There are five major causes of evolutionary change:

 

 

_________________________,

 

 

_________________________ _________________________,

 

 

_________________________ population size,

 

 

_________________________ mating, and

 

 

_________________________ _________________________

 

 

_________________________ (changes in DNA sequence) are the ultimate source of genetic variability

 

Mutations

 

•         _________________________ (changes in DNA sequence) are the ultimate source of genetic variability

•         Mutations are rare –

–        1 out of every 100,000 to 1,000,000 human gametes carries a mutation for a given gene

•         Mutations are the source of new alleles upon which natural selection can work, possibly resulting in evolution

 

 

•         Mutations are _________________________ goal-directed

 

Gene Flow

 

 

Gene flow is the movement of _________________________ form one population to another

 

 

This is accomplished through the migration of individual _________________________ from one population to another

 

Population Size

Genetic Drift is a change in allele frequency due to chance (random) events in small populations - Figure 15.2

Causes of Genetic Drift

 

 

  1. A _________________________  _________________________ is the dramatic reduction of a population as a consequence of a specific event (e.g., natural catastrophe, overhunting) – Figure 15.3

 

 

  1. The _________________________  _________________________ occurs when new populations are formed by a small number of organisms

 

Mating

 

 

Mating within a population is almost _________________________  random

Non-random mating, by itself, will not alter allele frequencies in a population

 

 

However, it can have large effects on the distribution of different _________________________  , and consequently the _________________________  , within a population

 

 

Certain genotypes may become more common, which can affect the “_________________________  ” of natural selection

 

Four important points about natural selection and evolution are:

 

 

(1) natural selection does _________________________ cause genetic changes in individuals;

(2) natural selection acts on individuals (unequal reproduction) but evolution occurs in

 

 

_________________________;

 

 

(3) the _________________________ of an organism is a measure of its reproductive success; and

 

 

(4) evolutionary changes are not _________________________ in an absolute sense, just relative to the environmental circumstances present at any particular time and place

 

How Does Natural Selection Work?

 

 

_________________________ _________________________ is primarily an issue of differential reproduction:

- Organisms with favorable alleles leave more offspring (who inherit those alleles) than do other individuals with less favorable alleles

 

 

Natural selection acts on the _________________________, which reflects the underlying _________________________

 

Selection can influence populations in three major ways

 

 

_________________________ selection shifts character traits in a specific direction:

it favors individuals at one end of a distribution range for a trait and selects against average individuals and those at the opposite extreme of the distribution

 

 

_________________________ selection acts against individuals who deviate too far from the average:

it favors individuals having an average value for a trait and selects against individuals with extreme values due to opposing environmental pressures

 

 

_________________________ selection adapts individuals within a population to different habitats:

it favors individuals at both ends of the distribution of a trait and selects against average individuals

Figure 15-8 (Selection Summary)

 

 

Opposing environmental pressures may produce _________________________

 

 

_________________________, in which two or more alleles are maintained in a population because each is favored by a separate environmental force

 

 

A variety of processes can cause natural selection

 

 

Organisms with reproductively successful _________________________ have the best

 

 

_________________________ (characteristics that help an individual survive and reproduce) to their particular environments

 

 

_________________________ for scarce resources favors the best-adapted individuals

When two species compete, as seen with predators and their prey, each exerts strong selection pressure on the other

 

When one evolves a new feature or modifies an old one, the other typically evolves new adaptations in response, a constant mutual feedback situation called

 

 

_________________________

 

 

_________________________ includes any situation where one organism (the predator) eats another (the prey)

 

 

_________________________ (individuals of different species live in direct contact for long periods) leads to the most intricate coevolutionary adaptations

 

 

_________________________ selection favors traits that help an organism mate

 

 

_________________________ selection favors altruistic behaviors

 

 

_________________________ is any behavior that endangers an individual or reduces its reproductive success but benefits other members of the species

If the altruistic individual helps relatives who possess the same alleles, this is called kin selection

 

 

Why Does Altruistic Behavior Exist?

If a mutation arose that caused altruistic behavior, wouldn’t that individual die (sacrifice itself)?

Perhaps, but what is “passed on?”

 

 

_________________________! 

 

Inclusive Fitness of an Individual

Is determined by the individual’s success at contributing its own genes to the next generation

It has two components:

 

 

1.  A _________________________ contribution from producing offspring, and

 

 

2.  An _________________________ contribution gained by helping relatives produce more offspring than would otherwise have been possible

 

Summary

This Chapter Has Covered:

1) The major forces causing evolution (mutation, migration, small population size, nonrandom mating, and natural selection)

2) The three ways that natural selection acts on populations (stabilizing, disruptive, and directional)

3) The results of natural selection