Mitosis & Meiosis Flashcards
What is the structure of DNA?
Double helix
Complimentary base pairs
Coils around nucleosomes
Coils again into supercoils and again into chromosomes
How many chromosomes in the human genome?
46 chromosomes (22 pairs + sex chromosomes xy)
Each human chromosomes contains a complex DNA duplex of …
10^7 bp and contain several hundred genes
Which is the long arm in a chromosome?
Q
Which is the short arm in a chromosome?
P
How are the long and short arm separated?
By the centromere
What dye is used to identify and analyse the G banding?
Giemsa
What dye is used to identify and analyse the Q banding?
Quinacrine
How many bands does G banding give?
400-500 bands / haploid human chromosome set
How long is each band in G-banding?
6-8 Mbp
What is mitosis for?
Producing two daughter cells
Genetically identical to parent cells
Growth
Replace dead cells
What happens in the S-phase?
DNA replication
Centrosome replication
What happens in prophase?
Chromatin condenses into chromosomes
Centrosomes nucleate microtubules and move to opposite poles of nucleus leaving a web of cytoskeleton filaments between them
What happens in prometaphase?
Nuclear membrane breaks done
Microtubules invade nuclear shape
Chromatids attach to microtubules
What happens in metaphase?
Chromosomes line up along equatorial plane (metaphase plate)
What happens in anaphase?
Sister chromatids separate and are pushed to opposite poles of the cell
What happens in telophase?
Nuclear membranes reform
Chromosomes unfold into chromatin
Cytokinesis begins
What drug is a inhibitor of kinesin spindle protein?
Ispinesib
What drugs inhibit the mitotic spindle?
Taxol
Vinca alkaloids ( vinblastine, vincristine )
What drug inhibits mitosis in the anaphase stage?
Colchicine
What happens in meiosis?
Only in gametes
Recombination of genetic material which generates diversity
Two cell divisions
4 haploid daughter cells
What is spermatogonia?
The process by which haploid spermatozoa develop from primordial germ cells by mitosis in the seminiferous tubules of the testis
When do meiotic divisions of sperm commence?
Puberty
What is oogonia?
A cell produced at an early stage in the formation of an ovum developed from primordial germ cells
How many mitoses to form a oogonia?
30
When do oogonia enter prophase of meiosis 1?
8th mouth of intrauterine life
When is meiosis 1 in egg cells completed?
Ovulation
When is meiosis 2 in egg cells completed?
When fertilisation occurs
What is non-disjunction?
Failure of chomosone pairs to separate in meiosis 1 or sister chromatids to separate properly in meiosis 2
What do most cases of down syndrome result from?
Regular trisomy 21
What is regular trisomy 21?
Most common chromosomal anomaly in humans, genetic condition caused by an extra chomosone
What is gonadal mosaicism?
A condition in which a post fertilisation mutation is confined to the gamete precursors and is not detected in somatic tissues
When does gonadal mosaicism occur?
When precursor germline cells to ova or spermatozoa are a mixture of two or more genetically different cell lines
One cell line is normal, the other mutated
What increases the chance of gonadal mosaicism?
Advancing paternal age
What is the most common inheritance patten for gonadal mosaicism?
Autosomal dominant and x-linked
Name conditions in which gonadal mosaicism is observed
Osteogenesis imperfecta
Duchenne muscular dystrophy
What is the purpose of the telomere?
Stops the chromosomes from unravelling
What happens to the telomere after each division?
They get shorter
What happens to cells that are mitotically inactive?
They done enter the all cycle, they enter G0
Is cytokinesis a phase in mitosis?
No
What is a characteristic of aggressive tumours?
Tumours with high mitotic figures
What happens in prophase in males?
Cytoplasm divides evenly
What happens to the cytoplasm during mitosis in females?
Cytoplasm divides unequally
What are microtubules made of?
Tubulin
