Matise - DNA Karyotype Flashcards
chromatin
DNA + histones
chromosome
Chromatin condense during phophase in order to form chromosomes
chromatid
after DNA is replicated it forms a pair of sister “chromatid” that are joined by a centromere
c-value enigma
genome size generally increases with the complexity of the organism but there is wide variety called the c-value enigma in which there are some seemingly simple protists that have larger genomes than humans.
(- side note - # of chromosomes does not correlate w complexity)
encode project
mapped the human genome for a bunch of different things like methyltion, site of transcription factors, etc. The main takeaway from this project is that what was viewed as “junk DNA” is actually super important in regulation. One theory while we still have some DNA that isn’t used is because it wasn’t particularly harmful evolutionarily so it was never outcompeted.
tandem repeats
If it is highly divergent from the normal genome then it must have happened along time ago. If it is mostly the same, then it is probably new. Allows for high levels of recombination. This is responsible for red-green color blindness. Both the red and green photoreceptor genes are on the X chromosome and are very similar with just a few bp’s being different. Recombination during meiosis causes the blindness.
contiguous gene syndromes
recombination occurs between large repeats, which causes a large insertion or deletion within a gene/chromosome. Causes DiGeorge (failure of pharyngeal pouches to develop) and Prader-willi/Angelman.
- Can be found with fish
short repeats
- micro-satellites
tandem repeats of sequences. Mostly at centromeres or telomeres. Widely used to identify specific chromosomes in genetic counseling because all 4 of the parental chromosomes are different.
retrotransposons
using a reverse transcriptase to go from RNA –> DNA and then inserting the DNA into a new genomic site.
Techniques for visualization of chromosomes: G banding
1) cells are incubated with colchicine, which prevents spindle formation by binding tubulinn. Cells get stuck in metaphase.
2) Stained with giemsa dye
- chromosomes are then identified based on size, banding pattern, length of p and q arms, and centromere position.
- detects relatively large changes like piece deletions and such.
Centromere position nomenclature
METAcentric - centromere in the middle
SUBMETAcentric - in between meta and acro
ACROcentric - centromere is at the top (acro=high)
- q = long arm
- p = short arm
Techniques for visualization of chromosomes: FISH
chromosome or chromatin are fixed to a slide and a probe is used in order to see where the gene is and if both chromosomes have the gene.
- is often done in interphase because it is faster but has less resolution.
- Can be done in metaphase too but DNA would have to be amplified and then incubation in colchicine.
- Better resolution than G-banding but you must know the sequence you are looking for so that you can make a proper probe.
Techniques for visualization of chromosomes: Comparative Genome Hybridization (CGH)
It is essentially a microarray that looks at the differences between a patients DNA and a normal persons DNA. It should be yellow but if you see Green then you know there was an insertion and if red then there was a deletion. Often used to screen newborns for insertions/deletions. Can’t be used to look for inversions or translocations. Good because you don’t need to know where to look and it also finds small mistakes.
Robertsonian translocation
Breakpoints occur within the centromeres of D and G group chromosomes. This causes a loss of p arms.
- D = 13-15
- G = 21,22
Pairing of homologous chromosomes will occur between 3 homologous chromosomes.
isochrome 21
a chromosome made up of two 21q arms. Viable because you are essentially diploid for 21. The offspring will either be monosomy 21 (lethal) or trisomy 21 (Down SYndrome)
