Human molecular genetics Flashcards
Natural selection requirements (4)
Variation
Inheritance
Selection
Time
Outline how natural selection lead to evolution
- Population with varied inherited traits
- Elimination of individuals with certain traits
- Reproduction of survivors
- Increasing frequency of traits that enhance survival
Components needed for DNA sequencing (5)
Known DNA template strand Primer DNA polymerase Deoxyribonucleotides Dideoxyribose nucleotides (ddNTPs)
What is dideoxyribose nucleotide
Terminating nucleotide
It is a modified nucleotide with an H attached to the 3rd carbon instead of OH which prevents the formation of phosphodiester bonds
What are the 4 dideoxyribose nucleotides
ddA
ddC
ddG
ddT
Outline the dideoxy chain termination method for sequencing DNA
A template DNA strand with known sequence is used. Primer is added to the template strand and extended by DNA polymerase by adding vv complementary deoxyribonucleotides. DNA synthesis will be terminated every time it encounters a dideoxynucleotide and asa result, DNA fragments of different sizes are generated. The DNA fragments are then passed through a capillary to be separated by size, shortest strand will travel the furthest and the longest strand will travel the least distance
Sequence is then read by a detector which sees the fluorescent tags and should be complimentary to the DNA we started with
Summarise the challenges face when large genomes are sequenced
- Mistakes can occur (in DNA replication) so the entire genome is sequenced several times over. Information about variation is retained
- assembling short sequences require a huge amount of computing power
- confusing parts such as repetitive regions can be resolved by comparing to a ‘reference genome’ or maps
Outline how a combination of DNA sequencing, recombinant DNA technology and computational method for aligning DNA sequence fragments enable large genome sequencing
Many copies of large chromosomal DNA is broken into overlapping chunks using ultrasound waves.
Recombinant DNA technology uses DNA ligase enzymes which are linkers, to ligate known sequence to each end of the unknown sequence
Then sequencing is done using primers to linkers where the same known linker is used as a primer to shotgun sequence all the unknown bits of DNA from the genome. This allows massive parallel sequencing platforms where the whole genome is being sequenced at the same time
Lastly, the sequences DNA that overlap can be aligned using computers and assemble into longer fragments or ‘contigs’. The computer ignores linker sequences (primers) and test each sequence for overlap with every other sequence and eventually resulting in a complete sequence of DNA
Explain how the 3 ways in finding protein-coding sequences (genes) in the genome
- Open Reading Frames (ORFs)
- Transcriptome analysis
- Comparative genomics
What are ORFs
stretches of DNA that appears to code for protein sequence begins with ATG (Methionine) and ends with a STOP codon. The sequence must in frame (in codon form - triplet of bases)
Computer algorithms can predict the presence of a gene by searching for what - 3 examples
TATA or GC box
ORFs
Splice sites
What is a transcriptome
Set of mRNAs transcribed by a particular cell or tissue, representing the genes that aWre coding for useful proteins in that cell or tissue
Outline transcriptome analysis
Make DNA copies of all the mRNA within a cell or tissue and sequence that
Should end up with a representation of the transcriptome of that particular cell or tissue (if cell is making mRNA from that gene then it must be useful)
Outline comparative genomics
Line up sequence of related genomic DNA and look for conserved/highly similar regions
What is a contig
Computer-assembled (virtual) regions of genome sequence made by aligning overlapping smaller sequence reads
