Gametogenesis 1 Flashcards
What is gametogenesis?
The process by which gametes (sperm and egg cells) are formed.
What does it mean that gametogenesis is compartmentalized in mammals?
It occurs separately from the development of somatic tissue.
What does gametogenesis include in animals?
Meiosis which is a unique cell cycle where there is recombination between homologous chromosomes to produce haploid cells.
What are primordial germ cells?
These are cells that are specified as germline cells, including in the gonads and in regions where they are specified before gonads.
What is the germ plasm?
A specialised cytoplasm in egg cells (not mammals) that predetermines germ cells. It is localised to one part of the egg.
What are examples of species that have a germ plasm?
Nematodes, insects and amphibians.
Where do primordial germ cells form?
In the posterior proximal epiblast.
What happens is primordial germ cells are cultured in vitro?
They form embryonic germ cells.
What does it mean that embryonic germ cells are pluripotent?
They can give rise to all cells of an adult, but not form an entire human.
What are PGCs called when they arrive at the genital ridge?
Gonocytes.
What happens when PGCs arrive at the gonad, in terms of division?
They divide mitotically.
How are parental genomes marked differently?
They are imprinted.
What are the phases of prophase in meiosis 1?
Leptotene, zygotene, pachytene, diplotene, diakinesis
What happens in the first phase of prophase in meiosis 1?
(Leptotene) - DNA replication is finished, sister chromatids are thin and closely associated and chromosomes begin condensing.
What happens in the second phase of prophase in meiosis 1?
(Zygotene) - There is bivalent formation and cohesin rings encircle sister chromatids. It requires a synaptonemal complex
What happens in the third phase of prophase in meiosis 1?
(Pachytene) - condensation continues, the synaptonemal complex breaks down, crossing over occurs.
What happens in the fourth phase of prophase in meiosis 1?
(Diplotene) - chiasmata are visible at the cross-over points, the synaptonemal complex breakdown is complete, homologous chromosomes separate and transcription occurs.
What happens in the fifth phase of prophase in meiosis 1?
Kinetochores move away from each other and the chromosomes remain joined at the tips.
What happens in metaphase 1?
There is nuclear membrane breakdown, the chromosomes assemble on the metaphase plate, spindle assembly checkpoint - the chromosomes must be properly aligned on spindles.
What does cyclin B do in metaphase 1?
It prevents degradation until the spindle assembly checkpoint is complete.
What is aneuploidy?
Having an abnormal number of chromosomes.
What happens in anaphase 1?
Homologous chromosomes separate.
What happens in telophase 1?
Two cytokinetic products form - each has a full set of homologous partners.
What is the other name for interkinesis and what is it?
Interphase II - it is a period of rest that some species have between meiosis I and II.
What is the difference between meiosis in males and females?
In males there is completion of meiosis II, but metaphase II is arrested in females until fertilisation.
What is non-dysjunction and when does it occur?
The failure of sister chromatids to separate properly during cell divison. It happens during anaphase I or II.
What are some of the conditions that arise as a result of non-dysjunction?
Down syndrome, Turner’s syndrome.
What is Turner’s syndrome?
Only one x chromosome is present - it is only a condition present in females. It is a neurological condition that can result in weight issues, heart problems and ovarian problems.
What is Klinefelter’s syndrome?
An extra X chromosome in men - can result in abnormal height, delayed puberty and sex organ defects.
