Evolution Test 4 Study Questions

What is the function of genes that affect longevity? Explain why selection acting on these genes has caused the evolution of senescence in multicellular animals.

The function is to allocate resources to reproduction and early life fitness Fitness gain in early life exceeds fitness loss from accumulation of damage. Pleiotrophic effects of genes involved are indirectly selected and expressed to show senescence.

Give three different reasons for why a point mutation might be neutral, or nearly so

1. Redundancy in genetic code 2. Some of amino acids in most proteins serve to connect proteins which can be done by many different proteins. Some amino acids just fill space and serve no purpose. 3. Some or perhaps majority of DNA can be changed without affecting organism in any detectable way.

What is meant by an "evolutionary species concept"?

A species is the present manifestation of an independent evolutionary lineage. Each species exist through different paths of evolution.

Molecular Clock

Constant rate that different amino acids and nucleotides sequences evolve. Used to estimate species divergence.

Explain why the allele that causes cystic fibrosis is not completely recessive.

Heterozygote for gene offers normal function as well as resistance to typhoid fever so there is a slight heterozygote advantage.

Age-Specific Mortality

Mortality rate of a specific age group

Rate of neutral evolution does not depend on population size.

Based of gene copies in genome so rate is proportional no matter number of organisms in population.

Why is selection acting on mutations affecting early-life fitness stronger than selection acting on mutations affecting late-life fitness?

Because not as many members of the population make it to the late-life. There is direct selection for early-life fitness which in turn lowers the selection on late-life fitness

Define and contrast the following evolutionary species concepts: biological species, ecological species

Biological Species Concept - A species is a collection of actually or potentially interbreeding individuals. Gene flow is responsible for cohesion of populations. Ecological Species Concept - A species is a collection of individuals who occupy the same ecological niche. Natural Selection is cohesive force for populations.

What do we call an individual who is heterozygous for a recessive, deleterious allele?

Carriers

Why do mice become geriatric after only two years of life?

Cells stop repairing itself and deterioration accumulates. Mice often die in first year of life from predators, accidents, and disease.

What is the cost of sex and why does it exist? In what types of organisms is the cost the highest, and in what types of organisms is there no such cost?

Cost of Sex - The selective disadvantage to sex from lower reproductive rate and success. Costs is highest when P<S and it is exaggerated. No such costs in asexual species.

Provide an example of a hereditary disease in humans that is caused by a completely recessive allele

Cystic Fibrosis Tay-Sachs Disease Spinal Muscular Atrophy Sickle Cell Anemia

What types of cells undergo senescence?

DNA, membranes, and other cellular components

For an asexual population, how high does the genomic rate of deleterious mutation have to be in order for deleterious mutations to accumulate faster than they can be eliminated by natural selection? What is the resulting evolutionary process called?

Deleterious mutations accumulate in asexual species over time. The critical mutation rate for asexual species is about one new mutation per genome per generation. Mutations accumulate until mean absolute fitness drops below 1 which is called mutational meltdown and the species rapidly goes extinct.

Allopatric

Describes population that is geographically separated and genes are not exchanged. Genetic drift leads to speciation.

Evolutionary Trajectory

Direction of evolution. Two species have the same evolutionary trajectory if they share the same evolutionary heritage or branch on the tree of life.

Neutral Theory of Molecular Evolution

Each gene copy has an equal chance of becoming mutated so the last unmutated copy will be pass down its info. The expected number of neutral mutations is two times the neutral mutation rate.

Reproductive Isolation Mechanism

Factors that prevent gene flow through the populations. Can be either Post-zygotic or Pre-zygotic.

Suppose that µf is the rate of mutation from a functional gene to a non-functional gene, and µb is the rate of mutation from a non-functional gene to a functional gene. What are the relative magnitudes of these two mutation rates, and why?

Functional to nonfunctional rate higher because there are more nonfunctional forms than functional terms. Harder to mutate to functional form cause mutation is specific.

Survivorship

Graph showing proportion of survivability at different ages within a population.

Why is it the case that most mutations that destroy the function of a protein-coding gene are recessive?

Homozygote of mutant allele lacks protein entirely so there is significantly reduced fitness. Heterozygote mutation still allows for enough of the protein to support normal metabolism.

What is inbreeding depression, and what causes it?

Inbreeding Depression - Elevated probability of homozygous recessive deleterious alleles that cause abnormalities due to similar DNA of parents.

Neutral Evolution us a result from what?

Interaction between mutation and genetic drift.

Provide an example demonstrating that natural populations possess genetic variation for longevity.

Life span of rats changing dramatically over short period of time. Different alleles and genes have been identified for senescence

Explain why different species have different maximum life spans.

Lifespan evolves from environmental aspects of predation and survivability where organisms put just enough energy into cell repair to stay alive and reproduce before they succumb to aspects of the environment. So if an organism has high risk of death then less energy will be put into cell repair and cells will begin to deteriorate sooner shorting lifespan.

Are the offspring of a sexual parent more or less genetically diverse than the offspring of an asexual parent?

More genetically diverse due to the mix of DNA from the parents.

Coadapted Gene Complex

Multi-locus genotype that produces a phenotype of high fitness as a result of interactions between genes that compose the complex.

Why is the DNA replicated prior to meiosis?

Must duplicated DNA before cell splits into two.

Deleterious Mutation

Mutation that negatively impacts the organisms ability to survive and reproduce.

How is it possible for a protein to have a different amino acid sequence in two different species even though it performs exactly the same function in both of those species?

Neutral mutations don't change the function of the protein formed from the sequence.

Is senescence an adaptation? Explain.

No, Senescence is not directly selected for but rather indirectly selected due to pleiotrophic effects of the genes involved. The direct selection is to increase early life fitness.

If an animal does not senesce, will it live forever? Why or why not?

No, it will eventual succumb to accidents, violence, or disease.

Is it common for animals living in the wild to die of old age? Why or why not?

No, many causes of death such as predation and disease.

Sympatric

Populations that are not geographically separated. Mating practices and dispersal may lead to speciation.

Positive Assortative Mating

Pre-zygotic isolation that prevents formation of hybrid zygote.

Explain the DNA repair hypothesis for the origin of intrachromosomal recombination. Describe four observations that support this hypothesis.

Proposes that meiotic crossing over original evolved as a mechanism to repair double stranded DNA. 1. Crossing-over occurs at site of repair. 2. Recombinational repair always occurs after replication where damage occurs. 3. Sometimes only very little portion is repair suggesting that main function is to replicate and crossing over is a by-productof meiosis. 4. When mutation rate goes up, so does the rate of recombination.

Explain why molecular data (DNA and protein sequences) are more useful than morphological data for the reconstruction of phylogenies.

Proteins formed by genetic info have molecular clocks that can tell when divergence occurs. More accurate than morphology studies of fossil record. Also, not every species is in fossil record.

18. Be able to estimate the mutation rate to a recessive, lethal allele if you are given data on the incidence at birth of homozygotes for that allele.

R*S

Mutation Rate

Rate at which mutation occurs over unit of time.

Rank the following four proteins according to the rate at which their amino acid sequences evolve: alpha-hemoglobin, cytochrome-C, fibrinopeptide, histone IV

Rate of sequence evolution is high for weakly constrained molecules. 1. Fibrinopeptide 2. Hemoglobin 3. cytochrome c 4. Histone IV

What is the mitochondrial theory of aging?

Says that the accumulation of damage in mitochondria over time leads to increased production of reactive oxygen species which cause cell damage. Suggests that repairing mitochondria can reduce rate of cellular damage or rate of senescence.

Describe the phylogenetic distribution of eukaryotes that reproduce exclusively asexually. What does this distribution suggest about the relative short-term and long-term advantages of sex and asex?

Sexual species give rise to asexual species which are usually short lived branches on a geologic timescale in eukaryotes. This suggests an advantage for sexual selection over the majority of history. Also that asexual may be favored in some situations on smaller time scale.

In the context of evolution by natural selection, what do we mean by a 'short-term advantage' versus a 'long-term advantage'?

Short-term Advantage- Increases fitness for time being but may be hurtful in long run. Long-Term Advantage - Best for long term survivability but may not be best for present.

Explain the mutation accumulation hypothesis for the evolution of senescence. Is there evidence to support this hypothesis?

States that nearly-neutral mutations accumulate over time and a subset of these drift into fixation. These genes only become expressed late in life and individuals in the wild rarely reach this point.

Explain the antagonistic pleiotropy hypothesis for the evolution of senescence. Is there evidence to support this hypothesis?

States that senescence is caused by alleles that increase reproductive success early in life at a cost for reproductive success later in life This hypothesis is favored by data.

Senescence

The deterioration of cells and tissues with age resulting in a late-life decline in fertility and survival probability. (Aging)

How large is the cost of sex for a species in which males are complete deadbeats (no paternal care) and they constitute 50% of the reproductive adults?

Two fold advantage for asex. (P=0,S=1/2)

Reproductive Isolation

Two population can no longer reproduce between each other. (Speciation) Determines speciation occurs or not.

Is it possible (in theory) for humans to avoid aging? Explain.

Yes, if germ-line cells can naturally divide without senescing through natural biochemical processes than it is possible.

2. List as many biological processes as you can in which mutation plays an important role.

junk dna

Provide an equation for the equilibrium frequency of a completely recessive, deleterious allele. Define all quantities in the equation

p^ = Square root of U/s p^ is Equilibrium frequency U is total rate of mutation s affect of mutation on fitness

Equation for Rate of Neutral Evolution

r= (2Nun NewMutantAlleles?Generation) x (1/2N Fixations/NewMutantAllele) N= Number of gene copies Un= Fixations per generation r= Rate of neutral evolution

Neutral Mutation

Changes in DNA sequence that are neither beneficial nor detrimental to the ability of an organism to survive and reproduce

Explain why the amino acid sequences of different proteins evolve at different rates.

Highmutation rate if sequence mutation doesn't affect function very much. Low evolution rate if sequence mutation is very deletrious. Depend on selection and constraints.

Reactive Oxygen Species

Reactive chemical containing oxygen. These are made by mitochondria and affect the rate of senescence.

Neutral Mutation Rate

Results from relationship between mutation and genetic drift This rate is independent of population size.

Speciation

The evolution of reproductive isolation between two populations.

What kind of organism was the last common ancestor of all living eukaryotes, and how did it reproduce? How do we know?

The first single celled common ancestor for all eukaryotes was sexual. We know through DNA and phylogenetic trends.

Why do most sexual species possess mechanisms that prevent mating between close relatives?

The inbreeding depression causes homozygous deleterious mutations witch significantly reduces fitness.

Describe three important features of eukaryotic sexual reproduction.

1. Alternation of fertilization and reductive division. 2. Interchromosomal recombination 3. Crossing-over between homologs 4. The repair of the double stranded DNA damage.

Provide four examples of cell lines that are immortal

1. Cancer cells 2. Germ line cells in animals 3. Meristematic cells in plants 4.

Provide three possible short-term advantages that sex may have over asex

1. Diverse genome is more adaptable to variable environment. 2. Parent produces offspring with fewer deleterious mutation than they have. 3. Repair of double stranded DNA

Provide two possible long-term advantages that sex may have over asex

1. Faster rate of evolutionary change that allows for more genetic diversity to withstand environmental change. 2. Helps get rid of deleterious mutations that can accumulate in asexual species.

Describe two approaches that are being taken to develop pharmaceuticals that will decrease the rate at which humans age.

1. Up-regulate repair mechanisms to an efficient rate of 100% 2. Slower the rate of accumulation of damage therefore slowing the rate of aging.

• Pre-zygotic reproductive isolation between sympatric species. • Post-zygotic reproductive isolation between sympatric species. • Pre-zygotic reproductive isolation between allopatric species. • Post-zygotic reproductive isolation between allopatric species.

1. prevent the formation of a hybrid zygote

12. Calculate the expected number of recessive lethal alleles carried by an average individual if you know the number of genes in the genome and rate of lethal mutation per gene, assuming that all lethal mutations are completely recessive.

80*lethal/indvidual