Genes and Genomes Flashcards
Definition of a genome.
The totality of genetic information belonging to a cell/organism (particularly the DNA that carries this info).
What is a chromosome?
The entire complement of genetic material in a chromosome set. Chromosome set = 1 copy of each unique chromosome.
What is the chromosome composition for females?
22 autosomes + X chromosome.
What is the chromosome composition for males?
22 autosomes + X + Y chromosomes.
True or false: Females have more DNA, males have bigger genomes.
True
Explain the C-value paradox.
C-value paradox = general trend of bigger genomes in more complex organisms, not a very good correlation.
Genetic diversity between species.
Diff orgs have diff genome sizes, etc. C-value paradox = that bigger orgs have bigger genomes. This is contested with the drosiphilia (fly) that has a MASSIVE genome.
What the definition of a gene?
Region of DNA transcribed as a single unit.
What is the function of a gene?
- Carries information for a discrete hereditary characteristic.
- Corresponds to a single protein/single functional RNA (gene products).
- Requires a promoter/some kind of regulatory DNA as a part of the gene.
Compare Prokaryotic and Eukaryotic Genes:
Prokaryotic:
- more simple.
- transcription and then translation.
- can have polycistronic genes with multiple gene products.
Eukaryotes:
- primary transcript
- 5’ capping
- RNA splicing
- 3’ polyadenylation
- exportation from nucleus into the cytoplasm
- translation
Define the term ‘exon’.
Expressed gene sequences.
Parts of the gene that are expressed/present in the FINAL, mature RNA form.
Define the term ‘intron’.
Intervening sequences.
Parts of a gene that are removed by splicing.
What are the two types of pseudogenes?
- Conventional
- Processed
Describe what a conventional pseudogene is. Use an example.
- B-globin is an example.
- Gene duplication occurs, creating two copies of the B-globin gene.
- 1st B-globin gene is still functioning. Therefore, the 2nd B-globin gene can undergo changes/mutations WITHOUT selection.
- Mutations affect promoter (affecting expression), coding sequence (e.g. nonsense and missense mutations), splicing sites, etc.
- Dysfunctional copy = pseudogene.
Explain what processed pseudogenes are.
- Processed pseudogenes = no longer have introns.
- Reverse transcriptase makes DNA copy of mRNA instead of the original a DNA.
- Double-stranded DNA version inserts somewhere else in the genome.
- Processed pseudogene = non-functional.
What are gene fragments?
Non-functional genes are broken up by chromosomal rearrangements into gene fragments.
Are pseudogenes common or uncommon?
Common throughout the genome.
What are the two different types of repetitive elements?
- Tandem repeats.
- Transposons.
What are tandem repeats?
- repeated end to end copies of short DNA sequences.
What two components make up Tandem Repeats?
- Microsatellites: tandem repeats of very short (1.6 bp) DNA sequence total array size approx. 10-150 bp. Known as: Short Tandem Repeats/Simple Sequence Repeats.
- Minisatellites: tandem repeats of short (7-100 bp) DNA sequence total array size approx. 100-20,000 bp.
What are transposons?
- Known as Jumping Genes!
- Parasitic genetic elements that can move about the genome.
What are the two types of transposition?
- Conservative Transposition (cut and paste).
- Transposons excised from the original position (leaving a characteristic mark) and inserted at a new location.
- DNA transposons move conservatively. - Replicative Transposition (copy and paste).
- Transposon inserts at a new location, BUT, an original copy remains.
- Retrotransposons move replicatively.
Can transposons cause disease? Provide two examples.
If a transposon inserts into a gene – affect the genes expression.
Example:
Haemophilia –> insertion of the retrotransposon L1 into the factor IX gene.
Muscular dystrophy –> L1 insertion into the dystrophin gene.
Explain the movement process of DNA transposons.
- Transposase gene transcribed and translated to make transposase protein.
- Transposase enzyme binds to the ITRs (inverted terminal repeats).
- Transposase enzyme catalyses excision of the DNA transposon from original site.
- Transposons moves and recognises specific sequence and the transposase enzyme catalyses the insertion of the transposon into a new site (into the TSD).
