Explain why sex-linked diseases are more common in human males.
- Since males have only one locus, the terms homozygous and heterozygous lack meaning for describing their sex-linked genes; the term hemizygous is used in such cases. Any male receiving the recessive allele from his mother will express the trait.
Describe the independent assortment of chromosomes during Meiosis I. Explain how independent assortment of chromosomes produces genetic recombination of unlinked genes.
- Independent assortment states that alleles are separate in the formation of gametes. This was applied in Meiosis I when the alleles were separated but since the two genes are located on different chromosomes and is thus unlinked. The random orientation of homologous chromosomes at metaphase I of meiosis, which leads to the independent assortment of the two unlinked genes
Distinguish between parental and recombinant phenotypes.
The parental phenotypes physical traits that are similar to their parents while the recombinant phenotypes have traits that aren't matched with their parents
Explain why linked genes do not assort independently. Explain how crossing over can unlink genes.
Because linked genes are within the same chromosome. In order for independent assortment to occur, the genes must be on different chromosomes.
Explain how nondisjunction can lead to aneuploidy.
Nondisjunction is a situation where a pair of homologous chromosomes fails to separate during meiosis I or meiosis II. Failure to separate causes aneuploidy which is a condition where a zygote will have an abnormal amount of chromosome.
Describe the structure of DNA. Explain the base-pairing rule and describe its significance.
Made out of two strands forming a double helix with the attachments of the sugar-phosphate backbones on the outside. There were also base pairings by following Chargaff's rule. There are also hydrogen bonds between the nitrogenous bases. Two H-bonds for A & T while G & C had three bonds.
Describe the semiconservative model of replication
This replication would contain two copies of one original strand and one new strand.
Describe the process of DNA replication, including the role of the origins of replication and replication forks.
1.) In the beginning, a site called origins of replication has short stretches of DNA that have specific sequence of nucleotides. 2.) Proteins that initiate DNA replication separates the two strands which opens a replication bubble. At each ends of the bubble there is the replication fork.
3.) The enzyme helicase untwists the double helix at the replication forks.
4.) Once separated single-strand binding proteins bind to the unpaired DNA allowing stabilization.
5.) The topoisomerase relieves the strain from the untwisting of the double helix.
6.) Primase starts an RNA chain from a single RNA nucleotide and adds more RNA nucleotides.
7.) In E.coli, DNA pol III adds a DNA nucleotide to the RNA primer and continues adding till it reaches to the RNA primer to the right where a Okazaki fragment is formed.
8.) DNA pol I comes in and replaces the RNA nucleotides with DNA nucleotides.
9.) Lastly, DNA ligase comes in and joins the sugar-phosphate backbones of all the Okazaki fragments into a continuous DNA strand.
Explain how RNA differs form DNA
a. RNA contains ribose as its sugar and DNA contains deoxyribose as its sugar
b. RNA contains the following nitrogenous bases: A, G, C, U
c. DNA contains the following nitrogenous bases: A, G, C, T
d. RNA is single stranded while DNA is double stranded
e. RNA is found in the nucleus but, unlike DNA, is also found outside of the nucleus
Briefly explain how information flows from gene to protein.
The sequence of nucleotides in DNA holds the instructions for making proteins but must first be transcribed into RNA nucleotides. RNA then takes the message out of the nucleus to the ribosomes, the site of protein synthesis. At the ribosomes, RNA is translated into amino acids to form a polypeptide that later folds to become a protein.
Distinguish between transcription and translation
Transcription is the copying of DNA nucleotides to RNA nucleotides. Translation is the conversion of RNA nucleotides (codons) into amino acids.
Compare where trancription and translation occur in eukaryotes
Transcription occurs in the nucleus and mRNA is transported to the cytoplasm, where translation occurs.
mRNA base triplets where there is an order of bases which codes for a amino acid.
Explain the relationship between the linear sequence of codons on mRNA and the linear sequence of amino acids in a polypeptide.
With 4 nitrogenous bases, there are 64 different possible
codons. Every 3 DNA nucleotides is transcribed into a mRNA codon. Because there are only 20 amino acids, more than one codon can code for a given amino acid but a codon can never be translated into more than one amino acid. There is one codon that translate to the amino acid methionine but is also the Start codon that signals the beginning of the translated region. There are also 3 Stop codons that signal the end of translation. The universal genetic code designates which codons translate to what amino acids.
Explain the evolutionary significance of a nearly universal genetic code.
The universal genetic coding system lets the codon for similar amino acids; therefore, allowing similar changes in humans and animals similar.
Explain the general process of transcription and the molecules involved.
Initiation begins when RNA polymerase binds with a promoter region of DNA and the DNA unwinds. The polymerase begins to add RNA nucleotides that are base paired to the template
strand of DNA. Elongation continues as the polymerase moves downstream, unwinding the DNA as it goes and adding RNA nucleotides in a 5' to 3' direction. The DNA will reform the
double helix as the RNA polymerase passes. Termination occurs when the polymerase reaches the terminator sequence and the RNA transcript is released and the polymerase drops off the DNA.
Describe the function of tRNA
The tRNA is the interpreter which transfers amino acids from the cytoplasmic pool of amino acids to a ribosome. Each tRNA molecule is used repeatedly.
Describe the structure and functions of ribosomes.
- Ribosomes facilitate the specific coupling of tRNA anticodons with mRNA codons during protein synthesis.
- RIbosome is made up of two subunits; large and small subunits
- Each ribosome has three binding sites of tRNA
- P site: holds the tRNA carrying the growing polypeptide chain
- A site: holds the tRNA carrying the next amino acid to be added to the chain
- E site: is where the discharged tRNAs leave the ribosome
Describe the process of translation and explain which enzymes, protein factors, and energy sources are needed for each stage.
Initiation brings together the mRNA transcript, the first tRNA carrying the first amino acid of the polypeptide and the 2 subunits of the ribosomes. This establishes the reading frame from this point on. Elongation continues as new amino acids are added one by one to the growing polypeptide strand as codon matching occurs between the codons on the mRNA and the incoming tRNA molecules. Termination occurs when one of the 3 Stop codons is encountered and instead of an amino acid, a release factor binds to the Stop codon site and signals the
release of the polypeptide strand. The ribosomal subunits then break apart.
Define "point mutations". Distinguish between base-pair substitutions and base-pair insertions. Give an example of each and note the significance of such changes.
A point mutation is a single change in a nucleotide base. With a base pair substitution, the wrong base pair is present but the overall number of base pairs is correct. This change may or may not have a significant effect on the protein made. If the change is in the 3rd base of a codon, because of redundancy in the genetic code, there will be no change in the amino acidtranslated and the protein will be the same. If the change is in the 1st
or 2nd spot, the amino acid translated will be different. It depends on the particular protein and where the change occurs if
this will greatly affect the protein. This type of change is called a missense mutation when an amino acid is coded for but just not the correct one. If the change causes a premature Stop codon, this is a nonsense mutation and can have a dramatic effect on the protein. If the change is an insertion of an extra base or the deletion of one, the reading frame will shift from that point on and cause extensive missense or nonsense.
Why is an insertion or deletion more likely to be deleterious than a substitution?
Insertion or deletion of nucleotides may alter the reading frame of the genetic message. A mutation called the framshift mutation occurs whenever the number of nuleotides inserted or deleted isn't a multiple of three. This will result in an extensive missense which makes the protein that is translated to be nonfunctional.
Define evolution and adaption
- Evolution: descent with modification. Also be defined as change in the genetic composition of a population from generation to generation or change over time.
- Adaption: characteristics of organisms that enhance their survival and reproduction in specific environments
Explain what Darwin meant by "descent with modification".
- Summarized Darwin's perception of the unity of life
- He thought that descendants of the ancestral organism lived in various habitats over millions of years had accumulated diverse modifications, or adaptions.
Describe the four observations.
1. Members of a population often vary greatly in their traits.
2. Traits are inherited from parents to offspring.
3. All species are capable of producing more offspring than their environment can support
4. Owing to lack of food or other resources, many of these offspring do not survive.
Describe the two inferences.
1. Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals.
2. This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.
Explain why an individual organism cannot evolve.
This is because once an individual's genetic material is changed; the individual will then produce offspring that will carry these traits. Eventually a population of the selected trait will arise.
Explain why natural selection can act only on heritable traits.
This is because the traits that were affected is only through traits that were only to be passed from generation to generation.
Describe how natural selection favors the evolution of drug-resistant pathogens.
When fighting against HIV, scientists use the drug 3TC which is designed to interfere with reverse transcriptase. The drug will kill many of the HIV infected cells but there are some that are resistant to this drug. Eventually the ones that were resistant to 3TC will replicate at a rapid rate; therefore, creating a population of HIV infected cells that are resistant to 3TC.
Explain how the existence of homologous and vestigial structures can be explained by Darwin's theory of natural selection.
- Homologous structure: anatomical resemblances that represent variations on a structural theme that was present in their common ancestor.
- Vestigial Structure: Remnants of features that served important functions in the organism's ancestors.
Explain the problem with the statement that Darwinism is "just a theory". Distinguish between the scientific and colloquial use the word "theory".
- The problem is that Darwinism has been proved with great deal of evidence
- In scientific terms, theory is a term where evidence has to back up. IN colloquial terms, theory means a hypothesis.
Explain the statement "It is the population, not the individual, that evolves."
This statement explains why a single individual of a species cannot evolve by itself because the individual will mate with its own kind and reproduce and this will occur until the population will carry the heritable traits.
Explain why the majority of point mutations are harmless
- The redundancy of genetic information prevents these mutations to be harmless.
- A point mutation in an area where the genome doesn't code for protein is usually harmless
- If there were a point mutation on the genome that codes for protein, it still wouldn't have any effect on the protein's function only if the amino acid composition isn't changed.
- Even if there was a change in the amino acid, this still wouldn't affect the protein's shape and function
Explain why mutation has little quantitative effect on allele frequencies in a large population.
Most mutations are not heritable because they do not effect any cell line leading to gametes and are thus preserved solely in the individual.
Define the terms population, species, and gene pool.
- Population: is a group of individuals of the same species that live in the same area and interbreed, producing fertile offspring.
- Species: individuals that are capable of interbreeding
- Gene Pool: consists of all the alleles for all the loci in all individuals of the population
List the five conditions that must be met for a population to remain in Hardy-Weinberg equilibrium.
- No mutations
- Random mating
- No natural selection
- Extremely large population size
- No gene flow
Explain the following statement: "Only natural selection leads to the adaptation of organisms to their environment."
Because natural selection is a process in which it takes existing traits that are effective in an environment and allows passing to next generations, the traits are then inherited which allows adaption to the environment for the offspring.
Explain the role of population size in genetic drift.
In genetic drift(chance events which fluctuates allele frequency unpredictably from one generation to the next), a smaller population is preferable because it will have a greater impact on the small population by allowing a higher percentage of successful inflictions towards the population vs. a larger population where the chance events would have less effect.
Distinguish between the bottleneck effect and the founder effect.
- Founder effect: Few individuals become isolated from a larger population and the outliers might create a new population whose gene pool differs from the larger population.
- Bottleneck effect: A sudden change in the environment, such as a fire or flood may drastically reduce the size of a population. This severe drop in population size causes this effect. The population may contain individuals who have certain alleles that are overrepresented, underrepresented, and maybe absent.
Describe how gene flow can act to reduce genetic differences between adjacent populations.
Gene flow takes place when alleles transfer between populations. This, in essence, blends the two populations together (over the generations) and reduces the genetic difference between them.
Define relative fitness.
Relative fitness is the relative chance of successful reproduction for any particular variant in the population.
Distinguish between intrasexual selection and intersexual selection.
Intrasexual selection is competition within a single sex. For example - a male competing against other males for mating privileges by fighting off other potential mates for a specific female. Intersexual selection occurs between different sexes. This is, in essence, mate choosing. Females often choose to mate with the flashiest or showiest males, for example.
Define Ernst Mayr's biological species concept.
Species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but don't produce viable, fertile offspring with members of other such groups.
Distinguish between prezygotic and postzygotic reproductive barriers.
A prezygotic barrier prevents mating between two species, or at least prevents fertilization of the egg. A postzygotic barrier impedes the hybrid from developing or becoming fertile.
Describe five prezygotic reproductive barriers and give an example of each.
1. Habitat Isolation: when species do not mate because they do not come into contact with each other (because they live in different habitats).
2. Temporal Isolation: when species do not mate with each other because they're mating seasons are in different times of the year, or they mate in different times of the day.
3. Behavioral Isolation: when an integral part of mating is the performance of a particular behavior that is unique to within the species.
4. Mechanical Isolation: when morphological differences prevent mating - such as different appearances between the species.
5. Gametic Isolation: when there is a physical barrier to egg fertilization - such as the sperm cannot penetrate the egg's membrane, or cannot survive in the reproductive tract of the other species.
Describe some limitations of the biological species concept.
The biological species concept cannot determine reproductive barriers in the fossil record, nor for a-sexual organisms like prokaryotes. It is also difficult to apply this concept to sexual organisms that we do not know very much about concerning reproductive behaviors, mechanics, etc.
Define phylogenetic species concept.
The phylogenetic species concept utilizes our newfound knowledge of DNA to classify species. The classification, more specifically, has to do as much with genetic history as with current genetic sequence. Both physical and molecular characteristics are used in this manner. Sometimes using DNA can reveal things that were unnoticeable with other species concepts, allowing us to separate incredibly similar species and relate incredibly different species. However, one disadvantage to this is it cannot be applied to most fossils, since it is hard to retrieve in tact DNA from them.
Distinguish between allopatric and sympatric speciation.
- Allopatric Speciation: Gene flow is interrupted when a population is divided into separate subpopulations.
- Sympatric Speciation: Speciation occurs in populations that live in the same geographic area
Describe the four stages of the hypothesis for the origin of life on Earth by chemical evolution.
1. Abiotic synthesis of small organic molecules
2. The joining of small molecules into macromolecules
3. Packaging of these molecules into "protobionts," droplets
4. Origin of self-replicating molecules that eventually made inheritance possible
Describe the contributions that Stanley Miller and Harold Urey made toward developing a model for the abiotic synthesis of organic molecules.
They were able to from amino acids with the addition of lightning to a reducing atmosphere
1. Some organic compounds from which the first life of Earth arose may have come from space
2. Carbon compounds have been found in some meteorites
Describe the evidence that suggests that RNA was the first genetic material. Explain the significance of the discovery of ribozymes.
1. RNA is central to information transfer in cells
2. RNA can be copied abiotically
3. Ribozymes have a variety of catalytic functions; pre-date enzymes
Describe the key events we talked about in class about the major events in the history of life on Earth
Explain the endosymbiotic theory for the evolution of the eukaryotic cell. Describe the evidence that supports this theory.
Explain the characteristic of Binomial nomenclature
• The two-part scientific name of a species is called a binomial
• The first part of the name is the genus to which the species belongs
• The second part, called the specific epithet, is unique for each species within the genus
• Both parts together name the species (not the specific epithet alone)
Explain the characteristics of Heirarchical classification
The first grouping is built into the binomial: species that appear closely related are grouped in to the same genus(this is usually done by finding the similar genus or first names)
- There are 8 classifications:
1)Domain 2)Kingdom 3)Phylum
4) Class 5)Order 6)Family
the named unit at any level
represents a hypothesis about evolutionary relationships
represents the divergence of two species
groups that share an immediate common ancestor
includes a branch to represent the last common ancestor of all taxa in the tree
a branch from which more than two groups emerge
Describe the structure, composition, and functions of prokaryotic cell walls.
- contains peptidoglycan, covered by a capsule, and has fimbriae sticking out
- maintains cell shape, provides physical protection, and prevents cell from bursting in hypotonic environment
Distinguish between the structure and staining properties of gram-positive and gram-negative bacteria
- Gram-positive: Simpler walls with many peptidoglycan
- Gram-negative: More complex walls with less peptidoglycan and has lipopolysaccharide layer
List the factors that give rise to high levels of genetic diversity in prokaryotes
- Rapid reproduction
- Genetic recombination
Explain rapid reproduction
Reproduce by binary fission
Although mutation rates are low during binary fiission, rapid reproduction increases the accumulation of mutations
Explain Genetic Recombination
Process where the prokaryotic DNA can be brought together by transformation, transduction, and conjugation
In general terms, describe the role of prokaryotes in the cycling of chemical elements between the biological and chemical components of ecosystems.
- Chemoheterotrophic prokaryotes function as decomposers
- Nitrogen-fixing prokaryotes add usable nitrogen to the environment
The use of organisms to remove pollutants from the environment
Explain why the kingdom Protista is no longer considered a legitimate taxon.
Some organisms that were formerly classified as protists have been found to be more closely related to organisms in other kingdoms.
Describe the different nutritional strategies of protists.
Protists can exhibit autotrophy, heterotrophy, or both in some cases (known as mixotrophy).
Name the five "supergroups" of eukaryotes. Which supergroups include multicellular kingdoms?
Describe the defining characteristics of each of the five supergroups.
1. Excavata - "excavated" groove along the body
2. Chromalveolata - membranous sac under plasma membrane; includes brown algae such as kelp
3. Rhizaria - contains most species of amoebas that have thread-like pseudopodia
4. Archaeplastida - red and green algae, along with land plants
5. Unikonta - amoebas with lobe or tube-shaped pseudopodia
Explain the significance of primary production by protists in aquatic communities.
• Many protists are important producers that obtain energy from the sun
• In aquatic environments, photosynthetic protists and prokaryotes are the main producers
• The availability of nutrients can affect the concentration of protists
Describe the characteristic that defines members of the kingdom Plantae.
- photoshynthetic autotrophs
- brown, red green
- cell walls made out of cellulose
Describe four characteristics that distinguish land plants from charophyte algae. Explain how these features are adaptive for life on land.
- First, the complexes that produce cellulose are rose shaped in both charophyceans and land plants.
- Next both have peroxisome enzymes that help minimize the loss of organic products from photorespiration.
- Third, the structure of their flagellated sperm is very similar.
- Finally, both form a phragmoplast during cell division.
Define and distinguish between the stages of the alternation of generations life cycle.
There is the haploid and diploid stage. The haploid stage starts as a single spore, which undergoes mitosis to form a gametophyte. The gametophyte produces gametes, which fuse during fertilization to form a diploid zygote. This starts the diploid stage. The diploid zygote undergoes mitosis to form a multicellular sporophyte - which releases spores.
Briefly describe the characteristics of the bryophytes.
Explain why most bryophytes grow close to the ground.
Bryophytes must grow close to the ground because they contain no vascular tissue to transport nutrients very far. Thus, every cell must be near water and nutrients to survive.
Briefly describe the characteristics of the seedless vascular plants.
Explain why seedless vascular plants are commonly found in damp habitats.
Gametophores in seedless vascular plants are fragile and can easily be destroyed in arid environments.They also have flagellated sperm which must swim to the female gametangia
Explain how vascular plants differ from bryophytes.
Vascular plants have vascular tissue which allows nutrients, water, and organic materials to be conducted to other cells. Bryophytes, on the other hand, must live near the ground to obtain their nutrients
Describe terrestrial adaptations that contributed to the success of seed plants.
Compare the size and independence of the gametophytes of bryophytes and seed plants.
Seedless vascular plants have tiny gametophytes that are visible to the naked eye. The gametophytes of seed plants are microscopically small and develop from spores in the sporangia of the parental sporophyte. The gametophytes of seed plants obtain nutrients from their parents, while the gametophytes of seedless vascular plants must fend for themselves.
Contrast homospory and heterospory.
Describe the ovule of a seed plant.
An ovule of a seed plant consists of the megasporangium, megaspores, and integuments.
Contrast the gametophytes of bryophytes and seed plants.
Male gametophytes travel long distances as pollen grains. The sperm of seed plants, unlike bryophytes, lack flagella and do not require a film of water, as they rely on the pollen tube to reach the egg cell within the ovule.
Explain why pollen grains were an important adaptation for successful reproduction on land.
Pollen grains were an important adaptation because the evolution of pollen allowed for pollination and contributed to the diversity of seed plants
Explain how a seed can be said to include contributions from three distinct generations.
Seeds can survive harsh conditions through dormancy, are distributed far from their parent sporophyte, and are multicellular.
Compare spores and seeds as dispersal stages in plant life cycles.
Moss spores can survive even if the local environment is too cold, too hot, or too dry for the moss plants themselves to survive. Because of their tiny size, the spores themselves can be dispersed in a dormant state to a new area.
The seed represents a different solution to resisting harsh environments and dispersing offspring. A multicellular seed is
more complex and resistant. After being released, a seed may remain dormant for days or years. Under favorable conditions, it germinates and the sporophyte embryo emerges as a seedling.
Describe the life history of a pine. Indicate which structures are part of the gametophyte generation and which are part of the sporophyte generation.
In most conifer species, each tree has both ovulate and pollen cones. The pine tree is the sporophyte. Each ovulate cone contains megasporangium. Microsporangium undergoes meiosis, producing haploid micropsores that develop into pollen grains. A pollen grain enters through the micropyle and germinates, forming a pollen tube that digests through the megasporangium. By meiosis, four haploid cells are produced. One survives as a megaspore. Female egg develops. Fertilization occurs as sperm and egg nuclei unite. The ovule becomes a seed.
Explain the process and function of double fertilization.
Double fertilization is a mechanism of fertilization in angiosperm in which two sperm cells unite with two cells in embryo sac to form the zygote and endosperm. One hypothesis for the function of double fertilization is that it synchronizes the development of food storage in the seed with development of the embryo.