genomics sem 2

cytogenetics

the study of chromosomes in health and disease

nucleosome

DNA wrapped around 8 histone proteins (octomer) highly compacted

euchromatin

• contains our genes 90% of genetic material

• can open and close at will- regualting gene expression via histone h1

• when in ppen form more accessible to transcription

heterochromatin

• compacted permanently

• less human chromasomes in this form

heterochromatin spreading

tendancy to spread into neighboring euchromatic regions-

recruitment of condenser proteins when it binds its permanent

barrier elements inbetween heterochromatin and euchromatin those regulate further recruitment of condensed protein stopping it from spilling over

structural heterochromatin

usually contains repetitive DNA sequences known as satellite DNA

found in centromeres and telomeres

telomeres

• mark the end of chromosomes

• they cap the ends of the chromosomes to prevent fusion

• when telomere becomes non functional - chromsomes fuse causing mis relocations in mitosis (causing abnormalities like cancer)

molecular cytogenetics

high resolution analysis for detection of specific DNA sewuences

the human genome project

first effort to determine the DNA sequence of the entire human genome

samger sequencing was used

sanger sequencing

dna clones to be sequences are generated by standard PCR reactions

clones subject to molymerase mediated synthesis setp

random termination of extension at each nucleotide position results in DNA fragments of varying sizes which can be analysed to show nucleotide sequence

whole genome shotgun sequencing

easier to do it all at once as saves time and money

annotation of the human genome

identifying the genes present

(earlier efforts only focused on non proteincoding genes)

how mnay protein coding genes in human genome

about 22,000

long non coding RNAs (IncRNAs)

• thousands exist- size varies

• some have been shown to play important roles in regulatin ggene transciption by interacting w DNA

• the function of the majority of them through has not been characterised

• their sequence is poorly conserved between species

microRNAs (miRNAs)

• these are tiny RNAs that bind to the 3’ UTR of mRNAs in order to regulate their translation

• highly conserved

• still discovering new ones

• tens of thousands probably exist

transposable elements (TEs)

• a large proportion of the genome is made up of highly reprititve transposon-based genes

• these transposable elements change their position and multiply within the genome

• the biolological role of TEs is still unclear but thought that theu may have a role in promoting genome evolution by reguqating genome complexity

LINEs

Long interspersed Nuclear Elements are a very common type of retroptransposon

three types (LINE-1, LINE-2, LINE-3)

LINE-1 most common

LTRs and ERVs

Long Terminal Repeats are usually associated w endogenous retroviral (ERV) sequences

these derive from retrovial sequences which have become non infectious but have maintained transposon activity

at some point in history they infected the germline and have been transmitted thru the popn