ch 15 Genetics terms
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maize cytogeneticist that discovered transposable elements
Ds trnasposable element
Ds for dissocation. Helps cause breakage of the chromosome. Considered nonautonomous element, meaning they require other elements for mobility
Ac transposable element
Ac for Activator, as it activates the breakage of chromosome 9 at the Ds locus. Autonomous element as it requires no other elements for mobility
In Maize coloring, when Irreversible c paired with:
a) C gene (wild type)
b) c-m (Ds) (no Ac)
c) c-m (Ds) (+Ac)
- a) pigmented
- b) colorless
- c) spotted kernels
- d) spotted kernels
enzyme required for the movvement of IS elements from one site in the chromosome to another. Binds the ends of Ac and Ds elements
IS (insertion-sequence) elements
Segments of bacterial DNA that can move from one position on a chromosome to a different position on the same chromosome or on a different chromosome. When they appear in the middle of genes, they interrupt the coding sequence and inactivate the expression of that gene.
One of two types of bacterial tansposons/ Contain a variety of genese that reside between two nearly identical IS elemnts that are oriented in opposite direction, and thus form IR (inverted repeat) sequence.
One of two types of bacterial tansposons which are flanked by IR sequences, but these sequences are short and do not encode the transposase enzyme necessary for transposition. Encode their own transposase in addition to carrying bacterial genes.
Fused circle created in replicative transposition; the donor and target plasmid temporarily fuse together to form a double plasmid, which gets cut at the two ends of Tn3 and the target sequence, whose free ends are fused together to create the cointegrate circle. It is then turned into two smaller circles, leaving one copy of the transposable element in each plasmid
A new copy of the transposable element is generated in the transposition event, with one copy at the new site and one copy at the old site.
No replication; instead the elemnt is excised from the chromosome or plasmid and is integrated into the new site. AKA "cut and paste"
plasmids carrying genes that encode resistance to several antibiotics
Transposable elements that employ reverse transcriptase to transpose through an RNA intermediate. Ex is Ty elements in yeast, copia elements in Drosophila
single stranded RNA virus that employs a double stranded DNA intermediate for replication. The RNA is copied into DNA by the enzyme reverse transcriptase.
long interspersed elements; move like a retrotransposon with the help of an element encoded reverse transcriptase but lack some structural features of retrovirus like elements, including LTRs.
short interspersed elementes; no reverse transcriptase. Best described as nonautonomous LINEs, because same structure, but no reverse transcriptase encoded. The most abundant SINE in humans is Alu, which makes up over 10% of human genome
region of the genome where there are few genes; a successful transposable element increases copy number without harming its host, and one way in which an element safely increases copy number is to target new insertions into these safe havens
P element in Drosophila
Transposable elemnte that was discovered as the cause of hybrid dysgenesis, a phenomenon that occurs when females from lab strains of D. melanogaster are mated with males derived from natural populations. Used in the lab to tag genes for cloning, or as a vector to introduce genes
Reverse transcriptase is needed for transposition of
_____ contain genes such as antibitoic resistance in addition to the genese needed for transposition
Describe possible consequences on gene expression when: a LINE inserts into an enhancer of a human gene
In the simplest scenario, the inersetion prevents the binding of transcriptional activators that are reqd for the ultimate binding of RNA poly to the promoter. Thus, the gene will not be expressed, as no mRNA will be synthesized
Describe possible consequences on gene expression when: a transposable elemente contains a binding site for a transcriptional repressor and inserts adjacent to a promoter
The presence of the transposable element will provide a binding site for the transcriptional repressor to bind near the promoter and prevent the binding of RNA poly II
Describe possible consequences on gene expression when: an Alu element inserts into the 3' splice (AG) site of an intron
the Alu element will be transcribed into RNA with the rest of the gene sequences and will prevent the splicing of the intron that is has inserted into. The insertion will almost certainly result in a null allele as the Alu sequence and the intron will now be translated. The intro, Alu, or both will probably contain stop codons.
Describe possible consequences on gene expression when: a Ds element that was inserted into the exon of a gene excises imperfectly and leaves 3 base pairs behind in the exon
The insertion and excision will result in a 3 bp indel in the exon and slighlty alter the amino acid sequence of the protein, but it won't produce frameshift mutation. The minor change in the amino acid sequence may or may not affect the function of the encoded protein
Describe possible consequences on gene expression when: an excision by the Ds element leaves 2 base pairs behind in the exon
This insertion and excision will cause a frameshift mutation and is more likely to impair protein function
Describe possible consequences on gene expression when: a Ds element that was inserted into the middle of an intron excises imperfectly and leaves 5 base pairs behind in the intron
Will likely not affect gene expression an the intron will probably still be spliced correctly
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