Chromosomes, Cell Division, Meiosis and Chromosome Abnormalities Flashcards
what is the structure of a eukaryotic chromosome?
Linear
telomeres at the edges
centromere in the middle
where are the regions of euchromatin and heterochromatin in a eukaryotic chromosome?
heterochromatin in the middle
euchromatin at the edges (however telomeres are composed of euchromatin)
what are the different phases in mitosis?
G1
S
G2
M
what happens in the G1 phase?
cell grows
what happens in the S phase?
DNA is replicated
what happens in the G2 phase?
cell prepares to divide
what happens in the M phase?
cell division (mitosis)
what are the 5 different phases of mitosis?
prophase metaphase anaphase telophase cytokinesis
what happens in prophase?
chromosomes condense
nuclear membrane disappears
spindle fibres form from the centriole
what happens in metaphase?
chromosomes aligned at the equator of the cell
attached by fibre to each centriole
maximum condensation of chromosomes
what happens in anaphase?
sister chromatids separate at centromere
separate longitudinally
move to opposite ends of the cell
what happens in telophase?
new nuclear membranes form
each new cell contains 46 chromosomes (diploid)
what happens in cytokinesis?
cytoplasm separates
what is a centromere?
constricted region which joins sister chromatids
what is the centromere composed of?
repetitive DNA sequences (satellite DNA)
also the site of the kinetochore
what is the kinetochore?
protein complex that binds to microtubules (involved in chromosome separation during cell division)
is the structure of heterochromatin condensed or open?
condensed (silenced)
is the structure of euchromatin condensed or open?
open (active)
what are the two tandemly repeated extragenic DNA sequences
satellite DNA
minisatellite DNA
what are the two types of extragenic sequences that make up approx. 45% of the genome?
SINEs (short interspersed nuclear elements)
LINEs (long interspersed nuclear elements)
what is the structure of chromatin?
DNA packaged with histone proteins
are histones positively or negatively charged?
positively charged
what are histones packaged into?
units called nucleosomes
what is the structure of a nucleosome?
146 base pairs of DNA (1.8 turns) wrapped around a core of 8 histone proteins
what does further “wrapping” of nucleosomes lead to?
formation of a solenoid structure, where the DNA is compacted by a factor of approx. 40
what are the 4 levels of condensed chromatin structure?
1: nucleosome
2: chromatin fibre
3: fibre-scaffold complex
4: chromosome
what are the purposes of packaging DNA?
negatively charged DNA neutralised by positively charged histone proteins
DNA takes up less space
Inactive DNA can be folded into inaccessible locations until required
what is the karyotype?
the number and visual appearance of the chromosomes in the cell nuclei of an organism or species.
what types of FISH probes are there?
unique sequence probes
centromeric probes
telomeric probes
whole chromosome probes
what does FISH stand for?
fluorescent in situ hybridisation
what is hybridisation?
he process of combining two complementary single-stranded DNA or RNA molecules and allowing them to form a single double-stranded molecule through base pairing.
what is meiosis?
cell division in germ cells
what creates genetic diversity in meiosis?
recombination of chromosomes
what do diploid cells divide into during meiosis?
haploid cells
what is oogenesis?
egg formation
what is spermatogenesis?
process of sperm formation
what goes through more divisions; eggs or sperm?
sperm - leads to a higher chance of mutation
what is produced along with the egg in oogenesis?
polar bodies
what happens in fertilisation?
two haploid cells form 1 diploid cell (zygote)
what determines the gender of the child in fertilisation?
if the sperm contains an X or a Y chromosome
where is mitochondrial DNA inherited from?
solely the mother
what is X inactivation?
when an X chromosome is randomly inactivated in a female zygote
