Meiosis Flashcards
What are the basic differences in the alignment process of chromosomes in mitosis vs meiosis?
Mitosis
Homologous chromosomes line up at the metaphase plate independently
Meiosis I
Homologous chromosomes are paired at the metaphase plate
Describe the structure of replicated chromosomes post chromosome replication
Replicated chromosomes align to form a bivalent - both (paternal and maternal) chromosomes run parallel
What are chiasma?
A structure that forms between a pair of homologous chromosomes by crossover recombination and physically links the homologous chromosomes during meiosis
When do chiasma develop?
In prophase I
Why is recombination important?
Its an important source of genetic diversity
What is a Holliday junction?
Deciding between Prague or Bilbao
Also
Holliday junctions provide a covalent link between recombining DNA molecules and need to be removed prior to chromosome segregation at mitosis. - A branched nucleic acid structure that contains four double-stranded arms joined together
You should listen to the lecture and write some notes on pairing + recombination of sex chromosomes in males here
Ye
What are the main two sources of genetic diversity?
Independent assortment of maternal and paternal homologs during meiosis I
Crossing-over during meiotic prophase I
What is MPF?
Maturation promoting factor
What things mediate meiosis?
Like many of the same molecules as mitosis
What is one thing that may cause an issue with correct meiotic division?
lacking degradation of cohesion complexes
What may occur in fertilisation following meiotic errors?
A meiotic I or II error may cause a trisomic zygote
What is uniparental disomy?
When someone receives two copies of a chromosome from one parent and none from the other
What uniparental disomy occurs after M1 error?
Uniparental heterodisomy
What uniparental disomy occurs after M1 error?
Uniparental isodisomy
What may occur from uniparental disomy?
Angelman and Prada-Willi Syndromes. Beckwith-Wiedemann syndrome.
How long does each stage of spermatogenesis take?
Spermatogonium -> primary spermatocyte or additional spermatogonia - 16 days
Primary spermatocytes -> Secondary spermatocytes via first meiotic division - 24 days
Secondary spermatocytes to spermatids via second meiotic division - a few hours
Spermatids -> sperm - 24 days
Describe when Meiosis I occurs in oogenesis
During fetal development meiosis 1 begins
After puberty, primary oocytes complete meiosis I, which produces a secondary oocyte and a first polar body that may or may not divide again
(2n Oogonium -> 2n Primary oocyte -> 1n first polar body + secondary oocyte)
Describe when Meiosis II occurs in oogenesis
The secondary oocyte begins meiosis II
A secondary oocyte (and first polar body) is ovulated
After fertilisation, meiosis II resumes, the oocyte splits into an ovum and a second polar body
(Secondary oocyte is ovulated and fertilised and splits into 2nd polar body and n+n ovum which becomes 2n zygote)
In where and when is there an arrest in gene division in fertilisation?
A long arrest at prophase 1 from second trimester to post birth
Do chromosome cohesion defects underlie maternal age effect?
Kinda but it aint so simple, eg trisomy 16 rates increase sharply between 18-21
