Chapter 6

Question 1

conditions of the hardy-weinberg equilibrium

Answer 1

The hardy-weinberg equilibrium= a situation in which allele and genotype frequencies in an ideal population do not change from one generation to the next. This equilibrium occurs when there is no selection, no mutation, no migration, no genetic drift and when random mating occurs.

Question 2

conclusions of the hardy-weinberg equilibrium

Answer 2

1 Conclusion 1 states the allele frequency in a population will not change generation after generation. Conclusion 2 states if the allele frequencies in a population are given by p and q, the genotype frequencies will be given by p2, 2pq and q2

Question 3

violation of hardy-weinberg equilibrium

Answer 3

Violation of the Hardy-weinberg equilibrium occurs when there is selection, there are mutations, there is migration, there are chance events, mates are not chosen at random

Question 4

what do the violations of the hardy weinberg equilibrium cause

Answer 4

Selection will cause the alleles at a certain point to comprise a larger portion of the total in the offspring generation than would be predicted. Mutations cause a change in gene frequency (new alleles are added) and act as a source for variation for selection and drift to act. Migration causes alleles to leave the population and enter a new population so gene frequency can either increase or decrease. Chance events such as weather changes, disease etc can wipe out individuals and decrease the genetic frequency, this may cause selection to occur. Mates not chosen at random means the genetic diversity will decrease and certain traits favorable to a mate will become more apparent in a population.

Question 5

when are heterozygotes favored?

Answer 5

Heterozygotes are favored in selection when negative-frequency dependent selection occurs. The heterozygotes are able to maintain allelic variation so when the fitness of one phenotype decreases, more offspring of the other phenotype can be produced. Furthermore, the AS genotype in Nigeria is beneficial because it prevents against malaria, but the SS genotype is harmful and causes sickle-cell anemia. In environments where malaria is not common

Question 6

when are homozygotes favored?

Answer 6

1 homozygous AA genotype is most common because there will be no risk of sickle-cell anemia without the A allele

Question 7

what is fixation and when does it occur?

Answer 7

Fixation occurs when all of the alternative alleles have disappeared so no genetic variation exists at a fixed locus within a population because all individuals are identical at that locus. Commonly occurs in small populations

Question 8

what is heterozygote superiority?

Answer 8

1 Heterozygous superiority is when a heterozygous individual is better able to survive than either homozygous individual. Ex. AS gene in Nigerians

Question 9

What is negative frequency-dependent selection?

Answer 9

Negative frequency dependent selection-rare genotypes have higher fitness than common genotypes. This process can maintain genetic variation within a population

Question 10

examples of neg frequeny selection

Answer 10

Orchids have 2 distinct morphologies to trick pollinators into coming and pollinating them when the pollinator learns the flowers have no nectar available, they quit pollinating them. Therefore, the flowers with the least common color are the most successful because pollinators do not recognize them

Question 11

what impact do mutations alone have on mutation?

Answer 11

Mutations inject new alleles into gene pools and change the allele frequency. Once a new mutation arises, drift and selection may begin to act on them

Question 12

Are mutations usually deleterious, beneficial, or neutral?

Answer 12

1 Mutations are normally neutral. If a mutation is deleterious, selection will act to decrease its frequency

Question 13

What is the relationship between population size and mutation impact?

Answer 13

1 Mutation rates for any given gene are low, but the rate at which mutations arise in the population is not. Considering the genome consists of 3.5 billion base pairs even a low mutation rate will be guaranteed to produce some mutations. There are about 9.8 billion new mutations arising in humans per year. mutations in a smaller population are more influential

Question 14

What is genetic drift? What are the important nuances of genetic drift with respect to evolution?

Answer 14

Genetic drift is a change in frequencies of allele copies in populations resulting from sampling error in drawing gametes from gene pool to make zygotes and from chance variation in the survival and/or reproductive success of individuals; resulting in non-adaptive evolution. Genetic drift is a NON-selection, RANDOM form of evolution. Genetic drift does NOT lead to adaptation. Small populations are most greatly influenced by genetic drift and results in a loss of heterozygosity.

Question 15

What are the differences between Selection and Genetic Drift and under what condition will each be important?

Answer 15

1 Selection is differential reproductive success that happens for a reason (in response to current environment). Selection is more common in large populations because small advantages in fitness can lead to large changes over the long term. Genetic drift is differential reproductive success that just happens resulting from random sampling error. Small populations are most greatly influenced and can cause a genetic bottleneck

Question 16

Not only be able to define sampling error, but understand its interaction with genetic drift, population size.

Answer 16

1 Sampling error means that the smaller the population there is, you are more likely to observe large deviations from the original frequency. In genetic drift, sampling error is very common because a small population changes frequently from the original.

Question 17

What is founder effect? What is its relationship with sampling error, genetic drift, population size, and conservation issues?

Answer 17

1 Founder effect is a new population started by a small number of individuals. the founder effect causes genetic drift because the new population is small and the frequency of alleles is not the same as a larger population.

Question 18

What are the problems and benefits of inbreeding? What can happen as a result of inbreeding? Under what conditions does inbreeding have a minimal impact?

Answer 18

1 In large populations, rare recessive alleles can be preserved in large populations, even if they’re deleterious b/c more common dominant alleles overshadow them. In inbreeding populations, rare deleterious alleles can become unmasked in homozygotes. That’s because parents are more likely to share the same allele than 2 random people. Inbreeding has minimal effect when there is a dominant allele present to mask the deleterious recessive allele

Question 19

What is inbreeding depression? Be able to define it. Know how to interpret value in figures

Answer 19

1 Inbreeding depression is a reduction in the average fitness of individuals relative to that of outbred individuals. it arises because rare, recessive alleles become expressed in a homozygous state when they can detrimentally affect the performance of individuals.

Question 20

In the book, section 6.7: the collapse of a dynasty is particularly interesting as problems associated with inbreeding. Be familiar with this example.

Answer 20

1 The Hapsburgs tended to marry within their extended family. It was common for 1st cousins to marry. Charles II was so inbred that he suffered from combined pituitary hormone deficiency and renal tubular acidrosis. The inbreeding also prevented Charles II to be infertile and unable to produce an heir. As the Hapsburg family became more inbred, only half of their children survived past age 1.

Question 21

What is coefficient of inbreeding (F)?

Answer 21

1 The coefficient of inbreeding is the probability that 2 alleles in an individual at a locus will be identical by descent. As F increases, fitness decreases.

Question 22

What is a selection coefficient? What do selection coefficient values tell you?

Answer 22

1 The selection coefficient is a measure of fitness. If S=0, fitness is the same between 2 genotypes. If S=1, one genotype is completely lethal.

Question 23

what is an extinction vortex?

Answer 23

1 Extinction vortex is the process a declining species undergoes when population size is driven down to extinction

Question 24

When dealing with conservation issues, what are the relationships between habitat fragmentation, population size, gene flow, inbreeding, homozygosity fitness, reproductive success, inbreeding depression, and extinction?

Answer 24

1 Habitat fragmentation gene flow because it prevents certain individuals from mating and reproducing. In turn, gene flow decreases within the population because similar/related individuals are forced to start reproducing. When inbreeding occurs, homozygosity fitness decreases because deleterious mutations can occur. When these harmful mutations occur, the reproductive success of the population declines, eventually resulting in extinction.

Question 25

With respect to in class discussion of conservation of Missouri collared lizards and Illinois prairie chickens, what were some of the actions taken prevent extinctions? Also, what were the genetic problems faced by both populations?

Answer 25

1 In the case of the collard lizards and greater prairie chickens, conservation biologists brought in collard lizzards and chickens from a separate population to reproduce with the endangered population. This was done to increase the genetic variation in the dying population and prevent genetic bottleneck.

Question 26

genetic locus

Answer 26

1 the specific location of a gene on a piece of DNA sequence on a chromosome. When mutations modify the sequence at a locus, they generate new alleles (variants of a particular gene or DNA region) alleles are mutually exclusive alternative states for a genetic locus

Question 27

population genetics

Answer 27

the study of the distribution of alleles within populations and the mechanisms that can cause allele frequencies to change overtime

Question 28

theorem

Answer 28

a mathematical statement that has been proved based on previously established theorems and axioms. Theorems use deductive reasoning and show that a statement necessarily follows from a series of hypotheses-the proof. Theorems are not the same as theories.

Question 29

genetic bottlenecks

Answer 29

events in which the number of individuals in a population is reduced drastically. Even if this dip in numbers is temporary, it can have lasting effects on the genetic variation of a population

Question 30

founder effect

Answer 30

a type of genetic drift describing the loss of allelic variation that accompanies founding of a new population from a very small number of individuals. this effect can cause the new population to differ considerably from the source population

Question 31

fitness

Answer 31

the success of an organism at surviving and reproducing. Thus contributing offspring to future generations

Question 32

relative fitness

Answer 32

the success of a genotype at producing new individuals standardized by success of other genotypes in the population

Question 33

average excess of fitness

Answer 33

the difference between the average fitness of an individual bearing the allele and the average fitness of the population as a whole

Question 34

pleiotrophy

Answer 34

the condition when a mutation in a single gene affects the expression of many different phenotypic traits. Considered to be antagonistic if a mutation with beneficial effects for one trait also causes detrimental effects on another trait

Question 35

negative selection

Answer 35

selection that decreases the frequency of alleles within a population. Occurs whenever the average excess for fitness of an allele is less than 0

Question 36

positive selection

Answer 36

selection that increases the frequency of alleles within a population. Positive selection occurs whenever the average excess for fitness of an allele is greater than 0

Question 37

epistasis

Answer 37

occurs when the effects of an allele at one genetic locus are modified by alleles at one or more other loci

Question 38

additive allele

Answer 38

an allele that yields twice the phenotypic effect when 2 copies are present at a given locus than when only a single copy is present. Additive alleles are not influenced by the presence of other alleles (e.g. there Is no dominance)

Question 39

negative frequency dependent selection

Answer 39

Negative frequency-dependent selection-rare genotypes have higher fitness than common genotypes. This process can maintain genetic variation within populations.

Question 40

inbreeding depression

Answer 40

a reduction in the average fitness of inbred individuals relative to that of outbred individuals. it arises because rare, recessive alleles become expressed in a homozygous state where they can detrimentally affect the performance of individuals