Organisation of the human genome Flashcards
The human genome
3 billion base pairs over 23 pairs of linear chromosomes
16,569bp in circular DNA makes up the mitochondrial genome
Around 1% encodes proteins
Exons around 1.5% (also encode rRNA and tRNA)
Protein coding genes
Single copy DNA
Average gene is 27kb with 9 exons
Non-coding DNA functions
Structural RNAs are rRNA, tRNA and snRNA
miRNA involved in gene regulation
lncRNA may be functional (Xist)
Globin genes
alpha cluster on chromosome 16 has 4 genes
Beta cluster on chromosome 11 has 5 genes
Retrotransposons
Transpose via an RNA intermediate
Retrovirus-like and LINE (long intersped nuclear elements) are viral
SINEs and processed pseudogenes are non-viral
DNA-DNA transposable elements
Transpose directly from DNA to DNA
Similar to bacterial transposons
None active in the human genome
LINE 1 element
500,000 copies in the human genome
Only 40-50 are active (mostly repressed through methylation)
No LTRs
Demethylation and increased transposition in tumours
Specific to germ cells, early embryos and neural progenitor cells
SINEs
Short interspersed nuclear elements
Genomic copies of small RNAs
Mostly belong to Alu family
Also copies of snRNAs and tRNAs
Alu sequences
150-300bp
10% of the human genome and found in other vertebrates
Transcribed to give RNA
Transpose using LINE reverse transcriptase
Sites of recombination
Satellite DNA
Simple sequence repetitive DNA
Minisatellite have repeat length of 15-100bp. 2-5p in microsatellites
Used in paternity testing, forensic analysis and gene mapping
Alu and disease
Homologous recombination between two Alu sequences, insertion into or near exons and aberrant Alu splicing from introns can cause disease
Rearrangements in the Mlvi oncogene occur via insertion of Alu transposon
