GN 1.1.3 Flashcards
What are the goals of meiosis?
creation of haploid gametes that upon fertilization will created diploid zygotes and generation of genetic diversity
What are homologous chromosomes?
Chromosomes that differ in parental origin
What are sister chromatids?
Two copies of a single chromosome produced by DNA replication
What is a bivalent?
Structure formed from association of homologous chromosomes.
What are the characteristics of meiosis 1?
Reductional division is which homologous chromosomes separate (2N to N).
What are the characteristics of meiosis 2?
Equatorial division in which sister chromatids are separated (2C to C) (N to N)
What is the key feature of homologous chromosome pairing?
Attachment of clustering telomeres at the nuclear envelope leading to rapid chromosome movement
What is the synaptonemal complex?
It acts as the glue that holds together homologous chromosomes
What is homologous recombination?
Programmed dsDNA breaks at “hot spots” leading to invasion into the chromatid by the homologous chromosome. Failure of a chromosome pair to undergo atleast one crossover event can lead to aneuploidy
What is happening in the leptotene stage of prophase 1?
Chromosome condensation, Bouquet formation, and double stranded breaks occur
What is happening at the zygotene stage of prophases 1?
pairing extends, AE matures into LE, and the synapsis begins
What is happening at the pachytene stage of prophase 1?
Completion of desynapsis and maturation of meiotic recombination sites into crossovers
What is happening at the diplotene stage of prophase 1?
Chromosomes undergo synapsis, homologues are held together by crossovers, and further condensation occurs
What are chiasmata?
Physical manifestations of genetic recombination that tethers homologous chromosomes; there are about 1-2 per homologous chromosome pair.
Abnormal crossovers are what?
Sub optimally placed exchanges are associates with non-disjunction
What is a cohesion and when is it added to the homologous chromosome?
Multi-protein complex that stabilizes the physical linkages that form as a result of homologous recombination added during development S phase.
Most aneuploidies have a high or low mortality rate?
HIGH
When does meiosis begin in males vs females?
Males starts at puberty and females starts at fetal development
What are the characteristics of meiosis in females?
Initiatied at 11-12 weeks of gestation in a fixed and finite pool
By birth all oocytes are arrested in the diplotene stage of meiosis I
Meiosis I is completed at ovulation and meiosis II is completed at fertilization
For men each cell that enters meiosis produces what?
4 haploid sperm
For females each cell that enters meiosis produces what?
A single mature egg and 2 polar bodies
Most meiotic errors are?
Maternal in origin
Do eggs or sperm have more stringent checkpoints?
Checkpoint mechanisms are more stringent in males, oogenesis is more robust but it can lead to more meiotic errors
As female birthing age increases the rate of trisomies?
Increases as well
What is non-disjunction?
When there is failure to separate and both sets of chromosomes go to a single cell
Why are cohesions a likely target for aneuploidy?
They are loaded on to chromosomes during fetal S phase. Which is required during chromosome segregation. The problem is that you are using older proteins the older you get
How does BPA affect meiosis?
BPA is weakly estrogenic, and it can lead to meiotic aneuploidy
Homologous chromosome pairing occurs in what phase?
Prophase 1
Synaptonemal complex formation occurs in what phase?
Prophase 1
Recombination and crossing over occurs in what phase?
Prophase 1
This is referred to as the tripartite structure that serves as the molecular glue holding together homologous chromosomes
Synaptonemal Complex
What is the order of the substages of Prophase 1?
Leptotene, Zygotene, Pachytene and diplotene
When is cohesion established?
Pre-meiotic S phase
Chromosome condensation, Bouquet formation, and double stranded breaks occur
Leptotene
pairing extends, AE matures into LE, and the synapsis begins
zygotene
Completion of synapsis and maturation of meiotic recombination sites into crossovers
Pachytene
Chromosomes undergo desynapsis, homologues are held together by crossovers, and further condensation occurs
Diplotene
Failure of a chromosome pair to undergo atleast one crossover event can lead to?
Aneuploidy
