Human Gene and Gene Mutation
Gene
Gene is DNA in the Chromosome/Chromotin In the Nucleus
Double Helix Structure of DNA
Semiconservative Replication of DNA
Transcription
Non-coding RNA
Regulation of Gene Expression
Epigenetic Modifications
DNA Modifications
Histone Modifications
Human Genome
What is Genome?
Coding sequences: < 5%
Repeat sequences: > 50%
Repeat Content of the Human Genome
Interspersed repeats
Transposon-derived repeats, four types:
LINEs
SINEs, including Alu
Long terminal repeat retrotransposons
DNA transposons
** The human genome does not contain any active DNA transposons.**
Processed pseudogenes
gene duplication
revers transcription and integration
Low copy repeats (LCRs)
blocks, 1-300kb, copied from one region into another, > 90% identity
Tandemly repeated sequences
Simple-sequence repeats (SSRs)
About Satellite DNAs
| Types | length of repeat unit | length of the Satellite | Example | Remark |
| Microsatellites | 1-5, 1-6, 1-10, 1-13 | less than 1000 bp | (CAG)n in Huntington’s disease, (CTG)n in myotonic dystrophy, (CGG)n in fragile X syndrome
Often called Short Tandem Repeats (STRs) in forensic genetics |
No complete consensus about the precise length limits
Vary in repeat times among individuals
Macrosatellites and Megasatellites may be used interchangablely |
| Minisatellites | 10 bp to few hundred bp | 1000-20000 bp | The telomeric DNA sequences, 10-15kb, (TTAGGG)n |
| Macrosatellites | several kb | | D4Z4, 3.3-kb unit, 1-150 times, which regulates local chromatin structure in a copy number dependent manner |
| Megasatellites | several kb | | RS447, 4.7-kb unit, 20-103 times |
Gene Family
Globin gene family: α-and β-globin gene clusters
Facts about human Genome
These variations can be
Harmless (change in phenotype)
Harmful (diabetes, cancer, heart disease)
Latent (e.g. susceptibility to heart attack)
Gene Mutation
Mutation & Polymorphism
Both are variations in DNA sequence: Substitutions, deletions, insertion, etc
Mutation: Frequency < 1% in a population; Gain of function or loss of function; Recent and RARE.
Polymorphism: Frequency > 1% in a population; Have a WEAK EFFECT or NO EFFECT at all; Ancient and COMMON.
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