BIOA01 Midterm

Evolution

changes in the genetic make-up (due to changes in allele frequency and genotype frequency) of populations over time

Natural selection

when there are inheritable variation in organisms, variants best suited for growth and reproduction in the given environment will occur in greater amounts in following generations

Inheritable variation

variations that can be passed on from the parents to the offspring because they impact gametes

Environmental variation

variation among individuals due to differences in their environment; for examples, apples on the same tree being different colours depending on how much sunlight they received

Genetic variation

differences in genotype among individuals of a population transmitted from parents to offspring that stem from mutations during DNA replication or environmental factors

The tree of life

the full set of evolutionary relationships among all organisms; makes predictions about the order that life appeared on earth

Descent with modification

evolutionary changes that have accumulated over time since the split of two lineages

How does evolution account for both the unity and the diversity of life?

Evolution suggests that all living things share the same common ancestor, meaning that all life is united because we all had the same starting point. Evolution also accounts for the diversity of life because of the genetic differences and changes that have differentiated species and life forms from each other.

How might heavy-handed use of antibiotics result in the increase of antibiotic resistant cells in bacterial populations?

Antibiotic resistant bacteria exists in low numbers in the absence of antibiotic use. Using antibiotics results in a selective pressure (i.e., natural selection will favour) for these bacteria, meaning that they are more likely to survive and reproduce and pass on their genes (horizontal gene transfer), meaning that the amount of antibiotic resistant bacteria will increase.

how is gene regulation expressed?

hierarchal; genes expressed at different stages in developmental processes control the expression of later acting genes

segmentation

the formation of discrete repeating parts or segments in the developing body of many animal embryos

oocyte

an unfertilized egg cell in animals produced by the mother, it is a developing female gamete

maternal-effect genes

those that are expressed by the mother that affect the phenotypes of the offspring, typically through composition or organization of oocyte

Would development happen normally if the mother has normal bicoid function, but the embryo does not? Why or why not?

yes, bicoid is a maternal-effect gene so the mother's phenotype affects the offspring's phenotype

loss of function mutation

genetic changes that inactivated the normal gene function

gain of function mutation

genetic change where a gene is expressed in the wrong place or at the wrong time

Phenotype

observable traits that can be influenced by genotype and the environment (for example, height, colour of butterfly wings)

Genotype

the set of alleles possessed by an individual

Population genetics

the study of patterns of genetic variation in natural populations

Populations

interbreeding groups of organisms of the same species living in the same area

Species

a group of individuals that are capable, through reproduction, of sharing alleles with one another

Gene pool

all the alleles present in all individuals in a population or species; individuals represent different combinations of these alleles

Mutation

changes in DNA sequencing that generate new variations in genotype; can be somatic or germ-line; necessary for genetic variation and evolution

Recombination

a process where pieces of DNA are broken and recombined to produce new combinations of alleles; shuffles mutations to produce new DNA sequences

Genetic drift

the random change in allele or genotype frequencies from generation or generation that occurs by chance; leads to evolution but not adaptation

Fixation

when an allele is present in 100% of a population; the change from a situation where there are at least two alleles to a situation where only one of the alleles remains

Somatic mutations

mutations that occur in somatic cells (nonreproductive cells); only affects the cell in which it originally occurred

Germ-line mutations

mutations that occur in reproductive cells and can be passed on from parents to offspring

Neutral mutations

have little to no effect on the organism, or do not effect their survival or reproduction

Deleterious mutations

mutations that are harmful to the organism

Advantageous mutations

mutations that improve chances of survival or reproduction

Speciation

when a group within a species separates from other members of its species and develops its own unique characteristics

Why are germ-line mutations more important in evolution than somatic ones?

Evolution requires changes to be inheritable, and only germ-line mutations can be passed along from generation to generation

Why is recombination critical to generating genetic variation?

recombination shuffles mutations, allowing for the creation of new alleles

Allele frequencies

the rate of occurrence of a specific allele in a population; provides information to make inferences about evolutionary processes based on patterns of genetic variation

How do you calculate allele frequency of allele X?

of allele X in population / total # of alleles

Fixed

When a population exhibits only one allele for a particular gene

Genotype frequency

the proportion in a population of each genotype (ex. Aa, AA, aa) of a particular gene or set of genes

Gel electrophoresis

separates segments of DNA according to their size; the proteins being studied move through a gel when an electrical charge is applied. The rate that they move through the gel depends on their charge and size

what are limitations to gel electrophoresis?

it only studies enzymes and can only detect mutations that resulted in amino acid substitutions that change the protein's mobility in gel

DNA sequencing

allows for population geneticists to find differences in DNA sequence; population samples are collected and the number of occurrences of a mutation is counted

What is genetic variation, and how is it measured?

the differences that exist between individuals within the nucleotide sequences of their genomes; measured by counting the number of individuals with observable differences (phenotypes) for a given trait, using gel electrophoresis to detect differences in the properties of enzymes encoded by variable nucleotide sequences, or performing direct sequencing of regions of DNA

Data on genetic variation in populations have become ever more precise over time, from phenotypes determined by a single gene to results obtained through gel electrophoresis that looks at variation among genes that encode for enzymes, to data generated directly from the DNA sequence. Has this increase in precision resulted in the discovery of more genetic variation or less?

More

What does it mean to say that an allele is "fixed" in a population?

the allele present is the only allele in the population; its frequency is 1 (100%)

can evolution occur if allele frequencies do not change?

yes, for example, genotype frequencies can changes although allele frequencies do not

What are the Hardy-Weinberg conditions?

There are no differences in the survival and reproductive success of individuals, the population is sufficiently large to prevent sampling errors, populations are not added to or subtracted from by migration, there is no mutation, individuals mate at random

selection

retention or elimination of mutations in a population

genetic drift

A change in the allele frequency of a population as a result of chance events rather than natural selection.

nonrandom mating

when mates are selected based on genotype or relatedness, affecting genotype frequency (but not allele frequency) from generation to generation

What does the Hardy-Weinberg principle predict?

the expected genotype frequencies from allele frequencies, so long as all conditions are met

What is the Hardy-Weinberg equation?

p^2 + 2pq + q^2 = 1

what are the primary mechanisms of evolution?

selection, genetic drift, migration, mutation, nonrandom mating

What can you conclude about a population whose allele frequencies are not in H-W equilibrium? What can you not conclude?

a population is undergoing evolution, but you do not know by which mechanism(s)

natural selection

the process that filters deleterious mutations out of a population in favour of advantageous ones and results in allele frequencies changing from generation to generation according to the allele's impact on survival and reproduction of individuals in the population; results in populations that are better suited for their environment

why do most populations, rather than expanding geometrically, remain stable in size from generation to generation?

the resources they rely on are limited, so members need to compete for survival and not all members can reproduce

competitive advantage

the result of how well an organism is adapted to their environment making them more likely to survive and reproduce

fitness

a measure of how much an individual's genotype is represented in the next generation

modern synthesis

combination of Darwin's theory of natural selection and Mendelian genetics, it is the current theory of evolution that was formed on Ronald Fisher's insight

positive selection

natural selection that increases the frequency of a favourable (advantageous) allele in a population

negative selection

natural selection that reduces the frequency of a deleterious allele

balancing selection

natural selection that maintains (at an intermediate frequency between o and 1) two or more alleles of a given gene in a population

heterozygote advantage

a form of balancing selection where the fitness of heterozygotes is higher than that of either homozygotes, resulting in selection that maintains both alleles at an intermediate frequency

stabilizing selection

a form of selection that selects against the extremes and maintains the "status quo"

directional selection

a form of selection that results in a shift of the mean value of a trait over time

artificial selection

a form of directional selection similar to natural selection, however it is done intentionally by humans, usually with a specific goals in mind

disruptive selection

selection the operates in favour of the extremes and agains intermediate forms (ie., against the average)

sexual selection

a form of selection that promotes traits that increase an individual's reproductive opportunities; can be intrasexual or intersexual

intrasexual selection

sexual selection where individuals of one sex (usually males) compete with one another for access to the other sex (usually females). Since competition is usually amongst males, they usually have the physical features such as large size and horns, fighting ability, etc.

intersexual selection

sexual selection involving interactions between males and females, where females choose a male. The males do not fight with other males for female attention, instead, they compete to attract females' attention with bright colours and displays (ex., the peacock's feather colours). Natural selection would work to get rid of these traits if not for sexual selection

population bottleneck

occurs when a large population is reduced to just a few individuals, perhaps resulting in marked loss of genetic diversity, and therefore genetic drift; usually temporary

founder event

a type of genetic drift that occurs when a few individuals of a population establish a new population; may be caused by change in allele frequencies of in a generation when those individuals arrive to and colonize a new land

does selection determine the fate of neutral mutations?

no, so they can cause genetic drift

migration

the movement of individuals from one population to another that results in gene flow; can be maladaptive

gene flow

the movement of alleles from one population to another through the interbreeding of populations; can result in homogenization of populations

interbreeding depression

a reduction in fitness resulting from mating between close relatives; causes homozygosity

homozygosity

the possession of two identical forms of a gene

Why, of all the evolutionary mechanisms, is selection the only one that can result in adaptation?

it is the only mechanism that acts in relation to the environment, since it changes allele frequencies based on how they contribute to the success of an individual's survival and reproduction

A female lizard floats on a log to an island where she lays her previously fertilized eggs and starts a new population on the island, where there are no other lizards. How do you think the genetic variation and allele frequencies of the island population will compare to those of the mainland population? Which mechanism of evolution is at work here?

it will likely be less extensive on the island, this is a founder event (genetic drift)

molecular evolution

evolution that occurs at the DNA level, which will result in genetic divergence of populations

genetic isolation

when genetic differences are too great for organisms to exchange genetic material

molecular clock

the correlation between the time for which two species have been evolutionarily separated and the amount of divergence between them

histone genes

genes that encode proteins that DNA warps around to form chromatin

what genes have the slowest molecular clock? why?

histone genes; negative selection has been effective at eliminating histone mutations that change amino acid functions (since many of these mutations are fatal)

pseudogenes

genes that are no longer functional

what genes have the fastest molecular clock? why?

pseudogenes; they are neutral so all mutations are seen as neutral

species

generally refers to a group of individuals that can exchange genetic material through interbreeding and produce fertile offspring

what does migration allow between populations?

gene flow; mutations from one population can spread to another population of the same species

closed gene pool

genes that can be shared among a species, but not with others

hybrid offspring

offspring produced through interbreeding through, typically closely related, different species

morphospecies

species that can be distinguished by morphology

hybridization

the interbreeding of two different species

incomplete reproductive isolation

when two individuals from different species are able to successfully mate, usually because boundaries between closely related species are not as strict; common in plants

niche

the combination of traits (i.e., nutritional and water needs, etc.) and habitat in which they exist

the ecological species concept (ESC)

species can be categorized by their ecological niche; there is a one-to-one correspondence between a species and its niche

the phylogenetic species concept (PSC)

members of a species all share a common ancestry and fate (since it is species that go extinct, not individuals)

pre-zygotic isolating factors

act before the fertilization of the egg; prevent fertilization and cause reproductive isolation in most species

post-zygotic isolating factors

act after the fertilization of the egg; result in failure of fertilized egg developing into fertile individual and typically involve genetic incompatibility

behavioural isolation

individuals only mate with others based on specific courtship rituals, songs, or behaviours

gametic isolation

the incompatibility between gametes of different individuals who typically belong to different species

mechanical incompatibility

the structural configuration of the genitalia that prevents individuals from one species from mating with individuals of another