Genetics Review & Variation Flashcards
What are the 3 components of nucleic acids?
Phosphate group, deoxyribose, nitrogenous base
What are the 4 bases of DNA and how many hydrogen bonds do they each make?
Adenine & Thymine (2 H bonds)
Guanine & Cytosine (3 bonds)
What type of genetic change is a SNP/SNV?
One nucleotide change/single substitution
Doesn’t alter surrounding sequence
What are the 2 types of SNPs/SNVs?
Transitions: SNV involving bases of similar shape (purine to purine- A>G, G>A, pyrimidine to pyrimidine - C>T, T>C)
Transversions: Bases of different shapes (opposite of transitions)
What functional impact(s) can SNPs/SNVs have on the gene/protein?
Synonymous: no amino acid change
Missense/nonsynonymous: changes amino acid sequence
Nonsense: new stop codon
Stop loss: loses stop codon
Splice site: alters mRNA splicing
What are small indels, and what types are there?
Small insertions and deletions; 1-1,000 bp
Simple: only 2 alleles - presence or absence
Framshift: within genes, indels alter reading frame for protein translation (alter all downstream codons). Indels of multiples of 3 (codon) do not cause frameshift mutations
What are the regulatory elements of genes and what do they do?
Promotor: starts transcription at 5’ end
Enhancer: increase expression levels
Insulator: decrease expression levels
Locus control region: enhance expression through chromatin context
Epigenetic controls: methylation, histone mods, histone variants, chromatin architecture
What is a pseudogene and where do they come from?
Look like genes, but don’t function
Two possible origins:
- Used to be functional but mutations ruined that
- Retrotransposition - mRNA back to DNA and integrated at a new locus
How many variants does each person have in their genome?
~4-5 million
What are microsatellites and what are the commonly used for?
Short tandem repeats (STRs)
Multiallelic, where alleles are determined by the number of repeats
It is commonly used for DNA fingerprinting and identity testing - only 20 loci are required
What are mobile elements?
Repetitive DNA elements that move in the genome (use retrotransposition)
What are CNVs?
Larger version of indels and microsatellites (1,000-3,000,000 bp) that are often found in regions of homology.
Biallelic: presence or absence
Multiallelic - multiple tandem copies
Alter gene dosage
What are inversions?
DNA segments found in two different orientations - often flanked by regions of homology.
How do mutations happen?
Errors in DNA replication/repair, recombination, chromosome segregation, mitosis/meiosis
What is the most common cause of mutation?
Spontaneous deamination - loss of an amine group of 5-methylcytosine to thymine at CpG sites
