AP Bio Tri 2 exam
Create a linkage map for these genes, showing the map unit distance between loci j,k: 12% j,m: 9% k,l: 6% l,m: 15%
--------------15--------------m-----9------j------6------I------6------k--------------12------------
38. Describe how a polypeptide to be secreted is transported to the endomembrane system
1. Polypeptide synthesis begins on a free ribosome 2. An SRP binds to the signal peptide, halting synthesis momentarily 3. The SRP binds to a receptor protein in the ER membrane, part of the complex that forms a pore and has a signal-cleaving enzyme 4. The SRP leaves, and polypeptide synthesis resumes, with simultaneous translocation across the membrane 5. The signal-cleaving enzyme cuts off the signal peptide 6. The rest of the completed polypeptide leaves the ribosome and folds into its final conformation
8. explain how three processes unique to meiosis generate a great deal of genetic variation?
1. independent assortment in metaphase I - each pair of homologous pair lines up independent of each other pair at the metaphase plate, so a daughter cell of meiosis I randomly inherits either a maternal or paternal chromosome. 2. crossing over - each chromosomes is not exclusively maternal or paternal, but includes regions at the ends of the chromatid from a nonsister chromatid this provides much additional diversity in the form of new combinations of alleles. 3. random fertilization - any sperm of a large number containing many possible genetic combination can fertilize any egg of a similarly large number of possible combinations.
15. What is the probability that a phenotypically normal child produced by a mating of two heterozygotes will be a carrier?
1/2
14. What is the probability that a mating between two carriers will produce an offspring with a recessively inherited disorder
1/4
1. how many chromosomes are there in the somatic cells of an animal in which 2n=16? how many chromosomes are in its gametes?
16 chromosomes in the somatic cells. 8 in gametes
2. if n=16, how many chromosomes are there in diploid somatic cell? how many sets of homologous chromosomes are in the gametes?
32 chromosomes in diploid somatic cell. 1 set of homologous chromosomes
3. if 2n=32, how many chromatids are there in a cell after duplication has occurred prior to cell division? What is the difference between sister chromatids and non-sister chromatids?
64 before duplication. Sister chromatids are produced when a chromosome duplicates before cell division, they are joined at the centromere and attached along their lengths. Nonsister chromatids are found on different chromosomes of a homologous pair (homologs
46. Explain how the following statement is inaccurate: "Antibiotics have created drug resistance in MRSA."
An environmental factor such as a drug does not create new traits such as drug resistance, but rather selects for traits among those that are already present in the population.An environmental factor such as a drug does not create new traits such as drug resistance, but rather selects for traits among those that are already present in the population.
20. What is the difference between an organism with a trisomy and a triploid organism?
An organism with a trisomy (2n +1) has an extra copy of one chromosome, usually caused by a nondisjunction during meiosis. A triploid organism (3n) has an extra set of chromosomes, possibly caused by a total nondisjunction in gamete formation.
50. Describe the assumptions and limitations of molecular clocks
Assumptions: the number of nucleotide substitutions in the related gene is proportional to the time that has elapsed since the genes branched from their common ancestor.
26. Describe the structure of the DNA molecule
DNA molecule is made up of a phosphate, sugar and base A double Helix Strand.
Bacterial DNA
DNA of most bacteria exists in the form of a single circular bacterial chromosome DNA is aggregated in a dense area of cell called the nucleoid Many bacteria contain other nonessential pieces of DNA called plasmids
47. How does evolution account for the similar mammalian forelimbs with different functions
Even though they have become adapted for different functions, the forelimbs of all mammals are constructed from the same basic skeletal elements and are homology
57. Distinguish genetic drift from gene flow in terms of (a) how they occur and (b) their implications for future genetic variation in a population.
Genetic drift results form chance event that cause alleles frequencies to fluctuate at random from generation to generation; within a population., this process tend to decrease gen. variation over time. gene flow is the exchange of alleles between populations; a process that can introduce new alleles to a pop. and hence may increase its genetic variation.
27. Describe the enzymes involved in DNA replication
Helicase: unwinds the DNA helix Primate: synthesizes RNA primers to act as a template for future Okazaki fragments to build on to DNA Polymerase lll: synthesizes nucleotides onto the leading strand in the 5' to 3' direction DNA Polymerase l: synthesized nucleotides onto primers on the lagging strand Ligase: "glues" together Okazaki fragments Telomerase: catalyzes the lengthening of telomeres Nuclease: cuts out unwanted/defective segments of nucleotides Topoisomerase: relives the winding strand Single strand binding proteins: prevents rebinding of the dna strands
9. many species can reproduce either sexually or asexually. explain what you think might be the evolutionary significance of the switch from asexual to sexual reproduction that occurs in some organisms when the environment becomes unfavorable
In asexual reproduction you produce a genetic clone of the organism. Thus there is no genetic variability. All the genes are the same. Sexual reproduction and crossing over in metaphase II of meiosis will allow for genetic variability to be produced. This is important evolutionary since this genetic variability will confer selective advantages/disadvantages on different individuals and will drive evolution (survival of the fittest) to adverse environmental changes.
16. incomplete dominance and epistasis are both terms that define genetic relationships. What is the most basic distinction between these terms
Incomplete dominance describes the relationship between two alleles of a single gene, whereas epistasis relates to the genetic relationship between two genes (and the respective alleles of each)
specific transcription factors
Increase the level of transcription in certain cell types or in response to signals
33. Describe the key steps of transcription as they occur in eukaryotes
Initiation: unwinds and unzips the DNA using the helicase elongation: RNA polymerase builds RNA and only adds nucleotides in the 5' to 3' termination: It separates from the DNA template.
35. Describe RNA processing in the eukaryotic cell
Introns are removed in the process of splicing by spliceosomes. In addition, a poly(A) tail is add to the 3' end and a 5' GTP cap is added to the 5' end. This process produces a final mRNA that is shorter than the transcribed RNA
31. In what three ways does RNA differ from DNA?
It forms a single strand sugar-phosphate chain. The sugar in its nucleotides is ribose. The base thymine is replaced by the base uracil.
53. If a population stopped reproducing sexually, how would its genetic variation be affected over time
Its genetic variation (whether measure at the level of the gene or at the level of nucleotide sequences) would probably drop over time. During meiosis, crossing over and the independent assortment of chromosomes produce many new combinations of alleles. in addition a population contains a vast numbers of mating combinations and fertilization of gametes of individuals with different genetic backgrounds. thus via crossing over, independent assortment of chromosomes, and fertilization, sexual reproduction reshuffled alleles into fresh combos each generation. without sexual reproduction new sources of genetic variation would be reduced, causing the overall amount of genetic variation to drop.
22. Why are males affected much more often than females by x-linked disorders?
Males only receive one X chromosome from the mother, while females receive one from each parent
39. Summarize the trp operon
Mechanism is continually "turned on" and is only "turned off" in the presence of high levels of the amino acid, tryptophan. Tryptophan is a product of the pathway that codes for the trp operon. Why tryptophan combines with the trp repressor protein, it causes the repressor to bind to the operator, which turns the operon "off," thereby blocking transcription. High levels of tryptophan acts to repress the further synthesis of tryptophan.
4. briefly describe the stages of meiosis 1 and meiosis 11
Meiosis 1: a. Interphase; Chromosome duplication; sister chromatids attached at centromere and by sister chromatid cohesion along their lengths b. Prophase I; Chromosomes condense, Synapsis of homologous pairs (held by synaptonemal complex); crossing over (exchange of corresponding DNA segments) is evident at chiasmata c. Metaphase I; Homologous pairs line up independently at metaphase plate d. Anaphase I; Homologous pairs of chromosomes separate and homologs move toward opposite poles; sister chromatids remain attached at centromere. e. Metaphase II; Haploid set of chromosomes, each consisting of two sister chromatids, aligns at metaphase plate; sister chromatids not identical due to crossing over. f. Anaphase II; Sister chromatids separate and move to opposite poles as individual chromosomes
5. compare mitosis and meiosis
Mitosis: - DNA replication occurs during interphase before mitosis begins, -one cell division, -synapsis of homologous chromosomes does not occur, -two (diploid) daughter cells produced which are genetically identical to parent cell, -enables multicellular adult to arise from zygote Meiosis: -DNA replication occurs during interphase before meiosis I begins, two cell divisions, -synapsis of homologous chromosomes occurs during prophase I along with crossing over between nonsister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion, -produces 4 (haploid) daughter cells, containing half as many chromosomes as parent cell, -genetically different, -produces gametes; reduces number of chromosome sets by half and introduces genetic variability
44. Summarize Darwin's mechanism of natural selection to explain observable patterns of evolution
Only those organisms most fit to survive will survive and reproduce. Observed: -each species produces more offspring than can survive -these offspring compete with one another for the limited resources available to them -Organisms in every population vary -The fittest offspring, or those with the most favorable traits, are the most likely to survive and therefore produce a second generation
24. Pedigrees; sex-linked dominant, sex-linked recessive, autosomal dominant and autosomal recessive
Pedigrees: A diagram that shows the occurrence of a genetic trait in several generations of a family. Sex-linked dominant: 1.) Both males and females are usually affected; often more females than males are affected 2.) affected fathers will pass the trait on to all their daughters and none of their sons 3.) affected mothers (if heterozygous) will pass the trait on to half of their sons and half of their daughters Sex-linked recessive: 1.) usually more males than females are affected 2.) affected sons are usually born to unaffected mothers; thus, the trait skips generations 4.) never passed from father to son 5.) all daughters of affected fathers are carriers 6.) all sons of affected mothers will be affected Autosomal dominant: 2.) both sexes transmit the trait to their offspring 4.) affected offspring must have an affected parent unless they possess a new mutation Autosomal recessive: 2.) tends to skip generations 3.) affected offspring are usually born to unaffected parents 4.) when both parents are heterozygous, approximately one-fourth of the offspring will be affected 5.) appears more frequently among the children of consanguine marriages
34. What is a promoter?
Site where RNA polymerase attaches to start transcription
10. a tall tea plant is crossed with a recessive dwarf pea plant. What will the phenotypic and phenotypic ratio of offspring be if the tall plant was TT? What if the plant was Tt?
TT x tt : All Tt and tall. Tt x tt: 1/2 Tt 1/2 tt 1/2 Tall 1/2 Dwarf
28. Contrast the leading and lagging strand
The leading strand is continuously synthesized in the direction of the replication fork in the 5'-3' direction. The lagging strand works away from the fork and is synthesized in Okazaki fragments with multiple RNA primers. They are both strands of DNA read in the 3'-5' direction, and they both become one strand in a new DNA molecule after being separated by helicase. The two new DNA molecules are identical.
17. If a man with type AB blood marries a woman with type O, what blood types would you expect in their children? what fraction would you expect of each type?
Type A: 1/2 Type B 1/2
51. Explain why genetic variation within a population is a prerequisite for evolution
Within a population, genetic differences among individuals provide the raw material on which natural selection and other mechanisms can act. Without such differences, allele frequencies could not change over time - and hence the population could not evolve.
18. with unlinked genes, an equal number of parental and recombinant offspring are produced. With linked genes, are more or fewer parental than recombinants produced? Explain your answer
You would expect that more parentals than recombinants, because linked genes have their loci on the same chromosome . Recombinants are the result of crossing over between non-sister chromatids of homologous chromosomes.
43. Describe the lytic and lysogenic cycles of viruses
after entering the bacterial cell and circulating, the phage DNA can immediately initiate the production of a large number of progeny phages (lytic cycle) or integrate into the bacterial chromosome (lysogenic cycle)
42. What characteristic does viruses share with cells?
both have genetic material, DNA, and both have nucleic acids and proteins, though in different forms
7. describe the process of crossing over
exchange of genetic material between homologous chromosomes that results in recombinant chromosomes during sexual reproduction.
6. how are the chrosomes in a cell at metaphase of mitosis similar to and different from the chromosomes in a cell at metaphase 11 of meiosis?
in mitosis they are in a vertical line down the center of the cell. In meiosis, they are in a horizontal line across the cell
48. Describe convergent evolution
independent evolution of similar features in different lineages
36. Contrast between introns and exons
introns are coding regions in mRNA. Exons are noncoding regions of mRNA and will be removed
52. Of all the mutations that occur in a populations why do only a small fraction become widespread?
many do not have a phenotypic affect on which natural selection can act others have a harmful affect, and are thus unlikely to increase in frequency because they decrease the reproductive success of their bearers. Since most mutations are at least slightly harmful, they do not benefit the organisms and it will not produce enough offspring to pass it on.
21. what do we mean by the wild type when studying population genetics?
most common phenotype seen in a wild population
49. Why is it important to distinguish homology from analogy to infer phylogeny?
phylogenic trees are based entirely on evolutionary relationships
41. What is apoptosis?
programmed cell death. Cannot stop once it has begun, so it is a highly regulated process. It is an important part of normal cell turnover in multicellular organisms
29. Chromosomes
structures found in the nucleus which contain all of the cell's DNA
25. Hershey and Chase
they found that when the bacteriophages infected bacteria only when the phosphorus entered and reproduced other viruses with phosphorous
23. Why are specific alleles of two genes that are farther apart more likely to show recombination than those of two closer genes
those that are close together on same chromosome - travel together during meiosis and do not usually sort independently
37. Describe the process of translation
turning mRNA into a protein. The mRNA attaches to the ribosome to initiate translation and "waits" for the appropriate amino acids to come to the ribosome. free-floating amino acids are piced up by and shuttled over to the ribosome by tRNA. tRNA carries and anticodon that binds with the codon on mRNA. Initiation: