Chromosomes Flashcards
Structure of (eukaryotic) chromosome
Linear Chromosome:
* Telomere
* Centromere
* Heterochromatin (gene-poor DNA)
* Euchromatin (“active” DNA)
breifly describe telomeres
structure and function
- Repeats (of 5’-TTAGGG-3’)
- Hundreds of copies at the ends of chromosomes
- Some lost at mitosis - end replication problem
- Telomerase
Function: protect DNA ends (shorten as age)
End-replication problem
The ends of linear DNA cannot be replicated completely during lagging strand DNA synthesis
name the 5 phases of mitosis
- Prophase
- Metaphase
- Anaphase
- Telophase
+Cytokenisis
PMAT
Prophase
- chromosomes condense
- nuclear membrane disappears
- spindle fibres form from the centriole
Metaphase
- chromosomes aligne at the equator of the cell
- attached by fibre to each centriole (by spindle fibres)
- Mex condensation of chromosome
Anaphase
- sister chromatids seperate at centromere
- Seperate longitudinally
- Move to opposire ends of cell
Telophase
- New nuclear membranes form
- Each cell contains 46 chromosomes (diploid)
Cytokinesis
- cytoplasm seperates
- Two new daughter cells
briefly explain centromeres
- Region joining sister chromatids
- Site of kinetochore attachement
- Required for chromosome seperation during cell division
what is chromatin
a mixture of DNA and proteins that form the chromosomes
what happens during interphase
weird question/answer ik - from PP
Genes are transcribes and DNA replication occurs (S phase)
Heterochramatin
what is it and structure
Inactive DNA with “silenced” genes - condensed structure
Euchromatin
what is it and structure
Active genes and open structure
Proportion of DNA that is protein coding
Not much: ~2%
what are extragenic sequences
DNA space between two genes of a genome
What can extragenic sequences include
- Tandemly repeated DNA sequences
satellite DNA
Minisatellite DNA - highly repeated interspersed DNA sequences - not sure what they are… no biological function
functions of non-coding DNA
- regulation of gene expression
as such, regulation of protein synthesis
What is the structure of chromatin
DNA packed with histone proteins to form chromatin
Packaged into units called nucleosomes
nucleosomes
segments of DNA wrapped around histone proteins - “beads on a string”
how does DNA bind to histones
charge (DNA -ve and histone +ve)
what does further wrapping of nucleosomes form
solenoid structure
packaging of DNA order
DNA-histone-nucleosomes-solanoid scaffold loop chromatids-chromosome
What is the purpose of packaging DNA
- -ve DNA neutralised by +ve histone proteins
- DNA takes up less space
what can we do to inactive dna
fold it into inaccessible locations until required
what is inactive chromatin characterised by
don’t need to know?
specific histone covalent modification
p arm
shortest arm on chromosome based on distance from centromere
Think: p = petite
q arm
longer arm on chromosome based on distance from centromere
karayotype
an individual’s complete set of chromosomes
number of chromosomes humans have
46 (23 pairs)
fluorescent in situ hybridisation - FISH
fluorescent DNA probes to target specific chromosomal locations within the nucleus, resulting in colored signals that can be detected using a fluorescent microscope
4 types of FISH probes and describe a bit about each/some of them
FISH = fluorescent in situ hybridisation
- Unique sequence probes
- Centrometic probes - determine chromo number
- Telomeric probes - detect subtelomeric rearrangements
- Whole chromosome probes - spectral karyotype, detect translocations and rearrangements
what is a germ cell
cells in the body that develop into sperm and eggs
Summarise meosis (start and end points not whole process)
- Cell division in germ cells
- Diploid cells (in ovaries and testes) divide to form haploid cells
- Chromosomes are passed on as re-arranged (recombined) copies - creates genetic diversity
what happens in chromosome numbers duuring meiosis and recombination
Diploid (2n) becomes two haploid (n) cells
46—> 2x23
summarise meiosis and recombination
single round of DNA replication but 2 rounds of cell division:
PMAT and then 2nd miotic division where attachment between sister chromatids is broken and they seperate
gametogenesis
production of gametes from haploid precursor cells
oogenesis
process of egg formation
spermatogenesis
process of sperm formation
difference between oogenesis and spermatogeneis in males and females
(both=gametogenesis)
- sperm go through more cells divisions - more chance on mutation
- Duration: sperm 60-65 days, eggs 10-50 years
- Commences: puberty in males and early embrionic life in females
- Gamete production per mitosis: 4 spermatids and 1ovum + 3 polar bodies
- Gamete production: 100-200 million per ejaculate compared to 1 ovum per menstrual cycle
- No. mitoses in gamete formation: 30-500 in males and 20-30 in females
see sheet
XX
female
XY
male
what determines gender of embryo
whether sperm contains X or Y chromosome
Fertilisation
Two haploid cells (egg, sperm) form 1 diploid cell (Zygote)
where does the embryo get its genetic material
assortment of genes from each original parent - inc genetic diversity
Where can the mitochondria and its DNA only come from
Mother via the egg - maternal inheritance
why does X-inactivation occur in females
females have a double does of gene product on X-chromosome
what does X-inactivation in females occur
random inactivation of one X chromosome - can result in funny things if mutation on one chromo and not the other
types of structural chromosome abnormalities
Four main types of structural chromosomal aberrations are deletion, duplication, inversion, and translocation
