3.2 chromosomes

prokaryotic chromosomes - types

prokaryotic chromosomes - types

single circular chromosome (naked) in nucleoid region

bacterial chromosome

circular plasmids

supercoiling: to compact into the cell

eykaryotic chromosomes - histones

multiple linear chromosomes

histones = globular proteins that dna wraps around → nucleosome

linker dna in bw nucleosomes

histone octamer: group of 7 histones

autoradiography

used to est the length of dna molecules in chromosomes

\depends on the emission of radioactive particles

sex determining region y

sry gene

expression initiates testicular dev

absence means default → female

haploid vs diploid

1 vs 2 complete sets of chromosomes

diploid: 1 set from father and mother each

karyographs

the arrangement of chroms according to their no., size, structure etc.

preparation:

take a sample of cells, centrifuge, undergo cell division, use dye to cause banding pattern, take photo using microscope, arrange.

human sex

female XX

male XY

X is bigger

down syndrome

trisomy 21 - extra chrom 21.

1st test: non-invasive nuchal translucency scan at 11-13 weeks. large amt of nuchal fluid associated w down syndrome

next: amniocentesis — get sample of amniotic fluid, prepare karyotype to determine. 16th week. ~1% miscarriage.

OR chorionic villus sampling — take sample of cells. 11th week. ~2% miscarriage.

syndromes

klinefelter syndrome — extra chrom 23 in a man (XXY)

turner syndrome — monosomy x (XO)