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29 Cards in this Set
- Front
- Back
Why is Drosophila useful as a model organism?
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-Simple and cheap breeding
-Short life cycle -High number of offspring -Polytene chromosomes |
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Polytene Chromosomes
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-large chromosomes in salivary glands of Drosophila
-many cell cycles w/o division -characteristic banding pattern -can see it during interphase |
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Life Cycle of Drosophila
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-Fertilization internal
-Female stores transferred sperm for several days -Male sexually mature in ~6hrs. -Female sexually mature in ~8 hrs. -Eggs deposited on surface of food source -1 day egg hatch and 1st larval stage -Arthropod - invertebrate having jointed limbs and a segmented body with an exoskeleton made of chitin -As grows sheds exoskeleton Review Slide egg --> 3 larval instars --> pupa --> imago --> adult fly |
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Calculate % Recombinance between 2 genes
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Example: Eye Color vs. Bristle Shape
White Straight --> 19+26+10+2 Red Curly --> 16+13+11+7 --> (104/523) x 100 = 19.9% --> linked *50% is the limit of the test |
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Calculate Interference
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I = 1 - Co
ex. --> I = 1 - .77 = .23 --> 23% of the time expected DCO's are not seen |
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Coefficient of Coincidence
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=(observed DCO/expected DCO)
expected DCO --> (freq. cross over between eye color & bristle shape)(freq. cross over between bristle shape & eye color)(total flies) ex --> observed/expected= 30/39 = .77 --> 77% of the time we see DCO when expected |
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How can you tell which loci are autosomal and which are X-linked
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-for X-linked loci, F1 males and F1 females have different phenotypes --> F1 males have same phenotype as mutant mother because he inherits his one X chromosome from her
-For autosomal loci, F1 males & females are both heterozygous & have the same phenotype |
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Polytene Chromosome Characteristics
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-Polytene chromosomes have undergone several rounds of DNA replication without cell division
-Polytene chromosomes are very large chromosomes that can be seen during interphase when cells are metabolically active -Polytene chromosomes are paired with their homolog in somatic cells (unusual) which makes them appear even larger -The banding pattern is specific to each chromosome which makes it easy to observe large chromosomal aberrations such as deletions, insertions, translocations and inversions -Each band spans about 30,000 bp – enough DNA to encode several genes |
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Why did we use Drosophila virilis for the polytene chromosome lab?
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Drosophila virilis is a larger fly & therefore has larger salivary glands that are easier to isolate
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Hyphae
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tiny filaments in fungi
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Mycelium
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interwoven mat of hyphae
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Ascospores
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form through meiosis in a sac called an ascus
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Why is studying a haploid organism useful?
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can see recessive mutations immediately
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Plasmogamy
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the union of cytoplasm of two gamete cells
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Karyogamy
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the union of the nuclei
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Dikaryon
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the state in certain fungi in which each compartment of a hypha contains two nuclei, each derived from a different parent
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Ascomyocytes
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-Karyogamy occurs within an ascus and the diploid nucleus divides by meiosis
-one mitotic division follows meiosis to produce 8 ascospores in each ascus |
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Spores
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-single cell
-haploid -resistant to harsh conditions |
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Antheridium
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-acts as male
-donates nuclei to ascogonium |
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Ascogonium
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acts as female
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Asexual Reproduction
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creates genetically identical spores
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When counting asci in Sordaria, which arrangements go together?
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-4:4 arrangement
-2:2:2:2 + 2:4:2 arrangements |
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Calculate freq. of recombinant asci
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ex. --> tan = (2:2:2:2 + 2:4:2)/total asci = 312/573 = .54 --> percentages of recombinant spores = .54/2 = 27%
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Polytene Chromosome Staining Procedure
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-place 3rd instar larva on slide with saline solution
-hold larva down and pull needle in head away from body to remove salivary glands -allow glands to soak in saline for 10 minutes (then blot it up) -place aceto-orcein stain on glands and let site for 15 mins -red nuclei appear -blot up old and place new drop of stain -squash to break open nuclei -observe chromosomes |
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Homologous Chromosomes Pair in what stage for polytene chromosomes
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prophase I of meiosis I
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Complementation Test
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-can determine if these mutations are alleles in the same gene or mutations in different genes
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Compensation Test
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-can determine which steps (enzymes) cn and v are related to in the biochemical pathway
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Importance of brown mutation in Drosophila
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The brown mutation is involved in making red pigment. Being homozygous for the brown mutation means there is no red pigment made. The brown pigment is easier to see in the absence of red pigment. With the brown mutation, one needs to distinguish between brown, peach, and white eyes. Without the brown mutation, one needs to distinguish between deep red & bright red eyes. Without the brown mutation, one might not be able to distinguish between the cinnabar & vermilion phenotypes.
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Are the mutations in the same or different gene pathways?
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-the phenotype of the cn/bw x v/bw F1 flies is brown eyes
-This means the mutations are in different genes in the pathway -Since the F1 flies habe one working copy of the gene to make E1 and one working copy of the gene to make E2, the F1 flies show the wild type phenotype of brown eyes indicating that the cn and v mutations are in different gene pathways |