1. PowerPoint to accompany CONCEPTS IN BIOLOGY
TWELFTH EDITION
Enger • Ross • Bailey
CHAPTER 12
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. Populations vs. species
A species is all the organisms potentially capable of naturally breeding among themselves and having offspring that could successfully interbreed.
A population is a group of organisms in the same species in the same geographical area.

3. Population genetics and gene pools
Population genetics is the study of the kinds of genes (alleles) within a population.
Also accounts for the numbers of alleles in a population
Predicts and observes how those numbers will change over time
This data is used to classify organisms and study evolutionary change.

4. Population genetics and gene pools
In a population
Each individual has a set of alleles.
Diploid organisms have 2 alleles at most.
The population may contain more different alleles than any one individual.
The human population has 3 alleles for blood type.
All of the alleles in a population make up the gene pool.

5. Genes, populations and gene pools

6. Biological species concept
According to the biological species concept species is a group of organisms
that share a common gene pool.
that are reproductively isolated from other populations.
Do not exchange genetic information with them.
Local populations of a single species may have slightly different allele combinations.

7. Gene and allele frequencies
Differences in gene frequencies reflect genetic differences between populations.
Allele frequency is a measure of how often an allele is found in a population.
Expressed as a decimal or percentage
# of times an allele appears in a population/the total number of alleles in the population

8. Allele frequencies differ in the human population.

9. Allele frequencies, dominance and recessiveness
Allele frequencies are unrelated to whether the allele is dominant or recessive.
There are many instances where a recessive allele is more frequent in a population.
Blue eyes & light hair are recessive traits that are more frequent in European regions.

10. Subspecies, breeds, varieties, strains and races
These all describe different forms of organisms that are all members of the same species.
Dogs have different breeds.
Plants have different varieties.
Bacteria have different strains.
Humans have different races.
All of these are types of subspecies.

11. Subspecies of water snakes

12. How genetic diversity comes about
Genetic diversity describes genetic differences among members of a population.
High genetic diversity implies that many different alleles exist in a population.
Low genetic diversity implies that all of the individuals in the population have the same alleles.
A gene pool with greater diversity is likely to contain combinations of alleles that will allow the individuals to adapt to a changing environment.

13. Mutations Mutations are changes in the base sequence of DNA.
Mutations are the source of new alleles.
All alleles originated with mutations.
Most mutations are harmful.
Occasionally a mutation will change a gene so that the protein works differently or better.
Example: insecticide resistance in mosquitoes

14. Sexual reproduction
Sexual reproduction generates new genetic combinations.
New combinations of alleles in individuals
May not necessarily change the frequency of alleles in a population
But the new combination of alleles in an individual may create a combination of traits that allows the individual to survive and reproduce more successfully than other individuals.
Example: Corn plants that inherit resistance to corn blight and resistance to insects

15. Migration
The migration is the movement of individuals into and out of populations.
Results in alleles being added or subtracted from a population
May change allele frequencies in the population
Artificial migration is used in zoos to generate genetic diversity.
Inbreeding has reduced genetic diversity in small zoo populations.
Zoos are exchanging animals for breeding to introduce new alleles into their populations.

16. The importance of population size
Population size is directly related to genetic diversity.
The smaller the population, the less genetic diversity a population can contain.
Mutations, migrations and death can have dramatic effects on the genetic make-up of a population.
Frequently, random events will significantly change the gene pool.
This is called genetic drift.

17. Genetic drift

18. Why genetically distinct populations exist
Many species have wide geographic distribution with reasonable distinct subspecies.
This occurs for several reasons.

19. Adaptation to local environmental conditions
Genetic diversity allows populations to adapt to their specific environments.
Some individuals will have combinations of alleles that allow them to survive and successfully reproduce in hostile conditions.
Death and migration remove or reduce the alleles that do not contribute to survival.
Example: Lizards in the desert have lighter coloration than those that live in other environments.

20. Founder effect
The founder effect is a type of genetic drift that occurs when a new population is established by a few colonizing individuals.
The small colonizing group may have different allele frequencies than the original population.
When the colonizing individuals mate and multiply, their allele frequencies will tend to persist, making the new population different from the parent population.

21. Genetic bottleneck
Genetic bottleneck is another form of genetic drift.
Occurs when there is a dramatic reduction in population size
Usually due to some chance event like a natural disaster
Could be due to over-hunting by humans
The remaining members of the population will mate and pass on their alleles, limiting their genetic diversity.
Many endangered species are undergoing genetic bottlenecks.

22. Barriers to movement
When migration is limited, populations become geographically and reproductively isolated.
Perpetuates the effects of genetic drift caused by founder effect and bottleneck
Limits genetic diversity and generates subspecies

23. Genetic diversity in domesticated plants and animals
Domesticated plants and animals are populations maintained by humans for human purposes.
Several techniques are used to produce plants and animals with specific characteristics.
High productivity, disease resistance, etc.
Low genetic diversity is an undesirable side effect.

24. Cloning
Cloning is the process of reproducing organisms asexually so that they are all genetically identical.
Generates clones
In plants, cuttings are used for this process.
Animals have recently been cloned by somatic cell nuclear transfer.

25. Cloning plants from cuttings

26. Selective breeding
Humans can bring together certain desired alleles by selective breeding.
Involves the careful selection of individuals with specific desirable traits and their controlled mating
Selective breeding has been used to
generate chicken breeds that grow quickly and generate a lot of meat or lay a lot of eggs.

27. Selective breeding
Intraspecific hybrids result from the crossing of two different varieties of the same species.
Interspecific hybrids result from the crossing of two species.
Tangelos come from crosses of tangerines and oranges.
Mules come from crosses between horses and donkeys.

28. Genetic engineering
Recombinant DNA technology has given us the ability to introduce alleles and modify the characteristics of domesticated species.
This has allowed agricultural scientists to engineer specific, valuable characteristics into certain species.
Generates genetically modified organisms (GMOs)

29. The impact of monoculture
Generates domesticated populations that are all similar with specific desirable traits.
Necessarily limits genetic diversity
Planting large crops of identical plants is called monoculture.
These are easy to maintain until a new disease comes along.
It may kill the entire crop because they are all identical.

30. Monoculture

31. The impact of monoculture
As a solution, scientists have generated gene banks.
These contain populations of primitive ancestors of domesticated species.
If a disease eliminated a given domesticated variety, then the ancestor could be used to regenerate the domesticated variety.

32. The banking of genes

33. Is it a species or not? The evidence
Testing the biological definition of a species may not be practical.
We cannot test each individual by breeding it with another.
Fossils cannot be tested.
Organisms that reproduce asexually cannot be tested.

34. Is it a species or not? The evidence
Therefore, we employ other species concepts to identify species.
The morphological species concept uses physical traits to identify species.
Behavioral differences can be used to differentiate species.
Differences in metabolism can be used to help distinguish among species.
The most precise way is to analyze differences in DNA sequences.

35. Human population genetics
All humans belong to the same species, but races and regional differences exist because our ancestors were more geographically isolated.
We are more mobile now, but non-random mate selection still occurs.
We tend to mate with people who are like us.
This means that certain diseases are prevalent in certain people groups.
Tay-Sachs disease and Ashkenazi Jews
Sickle-cell anemia and African ancestry

36. The frequency of the Tay-Sachs allele

37. Normal and sickle-shaped cells

38. Ethics and human population genetics
Understanding inheritance patterns has led to both bad and good human responses.
Eugenics (bad)
A movement motivated to purge the “bad” genes from society
Based on a fundamental misunderstanding of the power of inheritance
Disease treatment (good)
Understanding genetic diseases has allowed us to develop treatments.
PKU does not have to lead to mental retardation, if foods with phenylalanine are avoided.