1. Ch. 23 Thought Questions
AP Biology – Ms. Whipple

2. 12. What is Genetic Variation
12. What is Genetic Variation? How does this provide a platform for evolution?
Variations in individual genotypes leads to variation in individual phenotypes. Each individual of a species has a unique combinations of genes and will therefore be more/less adapted for their environment.

3. 13. In describing genetic variation, what is meant by the term Average Heterozygosity?
Population geneticists measure polymorphisms in a population by determining the amount of heterozygosity at the gene and molecular levels
Average heterozygosity measures the average percent of loci that are heterozygous in a population

4. 14. Describe Geographic Variation. How is a cline an example of this?
Geographic Variation refers to the differences in the genetic composition of various populations of the same species that are separated geographically.
A cline is a graded change in character along a geographic axis. This can be impacted by an environmental variable, such as temperature in Mummichog Fish on the East Coast.

5. 14. Describe Geographic Variation. How is a cline an example of this?

6. 15. What are the four sources of Genetic Variation within population
15. What are the four sources of Genetic Variation within population? Make sure you understand each.
Mutation causing the formation of new alleles for a gene. (substitution, frame shift)
Mutation altering gene position (translocation, inversion) or number of genes (gene duplication can be beneficial as it does not have severe effects but these genes may later be used for new functions)
Rapid Reproduction (i.e. bacteria & viruses) can cause an increase in mutation and genetic recombination causing rapid changes in a population.
Sexual Reproduction creates a unique organism with a unique combination of alleles causing genetic variation in a population.

7. 1. What is the smallest scale of evolution and why is this important to understand?
Microevolution is a change in allele frequencies in a population over generations
This is important to study because it is easily observable (Compared to macroevolution) and gives us insight into how populations relate to their environment from one generation to the next.

8. 2. Define the following terms:
Microevolution is a change in allele frequencies in a population over generations
Population is any group of the same species that live together and interbreed.
Population Genetics is the study of the genotypic and phenotypic ratios within a population, looking at allelic frequency.
Gene Pool is all the alleles for every locus in all members of a population.

9. 3. What is the Hardy-Weinberg Theorem and why does it appear to be an apparent contradiction to evolution?
The Hardy-Weinberg theorem describes the gene pool of a non- evolving population – DOES NOT EXIST IN NATURE but provides a baseline for us!!
This theorem states that the frequencies of alleles and genotypes in a population’s gene pool will remain constant over generations unless acted upon by agents other than Mendelian segregation and recombination of alleles.
The shuffling of alleles by meiosis and random fertilization has no effect on the overall gene pool of a population.

10. 4. What is Hardy-Weinberg equilibrium?
Hardy-Weinberg equilibrium describes the constant frequency of alleles in the gene pool of a non- evolving population.

11. 5. What are the five conditions for H-W equilibrium to be maintained?
The Hardy-Weinberg theorem describes a hypothetic population that is not evolving. However, real populations do evolve, and their allele and genotype frequencies do change over time.
That is because the five conditions for non-evolving populations are rarely met for long in nature.
A population must satisfy five conditions if it is to remain in Hardy-Weinberg equilibrium:
Extremely large population size. In small populations, chance fluctuations in the gene pool can cause genotype frequencies to change over time. These random changes are called genetic drift.
No gene flow. Gene flow, the transfer of alleles due to the migration of individuals or gametes between populations, can change the proportions of alleles.
No mutations. Introduction, loss, or modification of genes will alter the gene pool.
Random mating. If individuals pick mates with certain genotypes, or if inbreeding is common, the mixing of gametes will not be random.
No natural selection. Differential survival or reproductive success among genotypes will alter their frequencies.

12. 6. How can the H-W equation be used to today in terms of human health?
In such cases, we can use the Hardy-Weinberg equation to estimate genotype and allele frequencies.
We can use the theorem to estimate the percentage of the human population that carries the allele for the inherited disease phenylketonuria (PKU).
About 1 in 10,000 babies born in the United States is born with PKU, a metabolic condition that results in mental retardation and other problems if left untreated. The disease is caused by a recessive allele.
Is the U.S. population in Hardy-Weinberg equilibrium with respect to the PKU gene?
The U.S. population is very large.
Populations outside the United States have PKU allele frequencies similar to those seen in the United States, so gene flow will not alter allele frequencies significantly.
The mutation rate for the PKU gene is very low.
People do not choose their partners based on whether or not they carry the PKU allele, and inbreeding (marriage to close relatives) is rare in the United States.
Selection against PKU only acts against the rare heterozygous recessive individuals.

13. 6. How can the H-W equation be used to today in terms of human health?
From the epidemiological data, we know that frequency of homozygous recessive individuals (q2 in the Hardy-Weinberg theorem) = 1 in 10,000, or
The frequency of the recessive allele (q) is the square root of = 0.01.
The frequency of the dominant allele (p) is p = 1 ? q, or 1 ? 0.01 = 0.99.
The frequency of carriers (heterozygous individuals) is 2pq = 2 × 0.99 × = , or about 2%.
Thus, about 2% of the U.S. population carries the PKU allele.

14. 7. What are the two broad processes that make evolution possible?
Mutation & Sexual Reproduction

15. 8. What is the impact of the following:
Point Mutation is a change of a single base in a gene. The effects of point mutations can vary:
Mutations that result in a change in protein production are often harmful
Mutations that result in a change in protein production can sometimes increase the fit between organism and environment

16. 8. What is the impact of the following:
Gene Duplication
Duplication of large chromosome segments is usually harmful
Duplication of small pieces of DNA is sometimes less harmful and increases the genome size
Duplicated genes can take on new functions by further mutation

17. 8. What is the impact of the following:
Sexual Recombination: Sexual reproduction can shuffle existing alleles into new combinations (crossing over)
In organisms that reproduce sexually, recombination of alleles is more important than mutation in producing the genetic differences that make adaptation possible

18. 9. What is the relationship between mutation rates and generation span?
Mutation rates vary from organism to organism.
Mutation rates are low in animals and plants, averaging about 1 mutation in every 100,000 genes per generation.
In microorganisms and viruses with short generation spans, mutation rates are much higher and can rapidly generate genetic variation.

19. 10. Define the following:
Genetic drift describes how allele frequencies fluctuate unpredictably from one generation to the next.
Genetic drift tends to reduce genetic variation through losses of alleles
Founder effect is a type of Genetic Drift and occurs when a few individuals become isolated from a larger population
Allele frequencies in the small founder population can be different from those in the larger parent population
Bottleneck effect is a type of Genetic Drift and is a sudden reduction in population size due to a change in the environment
The resulting gene pool may no longer be reflective of the original population’s gene pool

22. 10. Define the following:
Gene flow is a change in the allele frequency due to transfer of alleles into or out of the pool

23. 11. Why would we discuss adaptive evolution and what role does natural selection play?
Of all the factors that can change a gene pool, only natural selection leads to adaptation of an organism to its environment.
Natural selection brings about adaptive evolution by acting on an organism’s phenotype
Natural selection accumulates and maintains favorable genotypes/phenotypes in a population.
Most populations have extensive genetic variation.

24. 12. Give examples of phenotypical variation that is not inheritable.
Not all variation is heritable. For example, body builders alter their phenotypes but do not pass on their huge muscles to their children.
Only the genetic component of variation can have evolutionary consequences as a result of natural selection.

25. 13. Explain the terms phenotypic polymorphism and genetic polymorphism in common terms giving an example from your own experience.
Genetic polymorphism means a gene existing in many forms in which at least two have high frequency (conventionally of1% or more). i.e having multiple alleles. For example, I have attached earlobes while my sister does not. Attached earlobes make up about 10% of the population.
Phenotypic polymorphism means that there are many different ways of expressing the same genotype, or that the phenotype takes more than one form. For example, two animals of the same species with the same genotype may look slightly different because they live in different habitats. Twins with the same genotypes will have varying phenotypes based on environmental (or epigenetic?) factors.

26. 14. How do we measure genetic variation?
To measure genetic variation you determine average heterozygosity of a gene within a population.

27. 15. How can very small differences in nucleotide sequences lead to such diversity in the human population?
Since nucleotide sequences are crucial for identification of an organism, a small change in one sequence can alter every generation after that specific mutation. If the nucleotide change leads to a phenotypic change that is noticeable and not bad/beneficial for the population then this phenotypic change may be allowed to survive in the species and is expressed. The more of these types of changes, the more diverse the population!
This leads to such diversity in the human population because of all the different traits and possible combination of traits in our gene pool.

28. 16. What is different about the terms fitness and relative fitness?
Fitness is the reproductive success according to a lifestyle which makes that particualr organism thrive.
Relative fitness is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals
Selection favors certain genotypes by acting on the phenotypes of certain organisms

29. 17. Why is it said that evolution acts on phenotypes and not genotypes?
Evolution is said to act on the phenotype first because it is the phenotype that is selected to survive and reproduce (although it is the genes of an organism that control the expression of a phenotype). For example., female deer chose their males based on the size (phenotype) of their antlers!

30. Three modes of selection:
18. Use the diagram below to differentiate between the modes of selection.
Three modes of selection:
Directional selection favors individuals at one end of the phenotypic range
Disruptive selection favors individuals at both extremes of the phenotypic range
Stabilizing selection favors intermediate variants and acts against extreme phenotypes

31. Frequency of individuals
Fig
Original population
Frequency of individuals
Phenotypes (fur color)
Original
population
Evolved
population
Figure Modes of selection
(a) Directional selection
(b) Disruptive selection
(c) Stabilizing selection

32. 19. Why does diploidy preserve genetic variation?
It allows recessive and dominant traits to continue to exist and be passed on. If both parents give a recessive trait, the trait will persist. Even if a heterozygote is born, the heterozygote has potential pass on the trait if matched another who is heterozygote or homozygous for the recessive trait. This increases genetic variation in a population.

33. 20. How does balancing natural selection relate to the term balanced polymorphism?
Balancing natural selection occurs when natural selection keeps stable frequencies of phenotypic forms. This state is called balanced polymorphism.

34. 21. Define and give an example of the following:
Heterozygote advantage: ​This is when heterozygotes having greater fitness levels than homozygotes. An example is that heterozygotes are more resistant to the severest effects of malaria.
Frequency dependent selection: This is the fitness of one morph declines because it is too common. When a type of moth becomes too common, jays learn to prey on it more quickly.
Neutral variation​: This is variation that has little to no impact of reproductive success. Half of the amino-acid changing mutations in Drosophilia have no selective effect.

35. 21. Define and give an example of the following:
Sexual dimorphism​: This is marked differences between sexes in secondary sex characteristics. An example is how males are generally the showier sex in a species.
Intrasexual selection​: This is selection within the same sex. An example is when a male monitors a group of females to make sure no other males express interest.
Intersexual selection: ​This type of selection is when individuals of one sex are picky in selecting mates. An example is how females select their male based on the male's showiness.

36. 22. What are the limitations to Natural Selection?
It is limited by time constraints
adaptations are often compromises that don’t bring about best benefit for the species
chance and anatural selection interact
It can only edit existing variations