14.4 Cellular Reproduction Flashcards
3 roles for meiosis
- Gametic or terminal meiosis
- Zygotic or Initial Meiosis
- Sporic or Intermediate Meiosis
Gametic or terminal meiosis
- All multicellular organisms
- Primary role is formation of gametes
Zygotic or Initial Meiosis
- Protists and Fungi
- Meiotic divisions occur just after fertilization to produce haploid spores
- Spores mitotically divide to produce haploid adult generation
- division occur after fertilization and produce haploid.
Sporic or Intermediate Meiosis
- Plants and some algae
- Meiosis not used to produce gametes
- Gametes produced by mitotic divisions of haploid gametophyte
Meiosis in Vertebrate Males
- males, meiosis occurs before the full differentiation of the sperm. Differeiation of spermatids is after.
- spermatogonia: special type of stem cell. Undergo mitotic divisions then meiosis.
- Males: Meiosis occurs before differentiation of sperm
- Produces four viable gametes
Meiosis in Vertebrate Females
- Females: Meiotic divisions occur after differentiation
- Produces only one fertilizable egg
- Oogonia for eggs. grow to full size egg cell before undergo two meiosis. In devo of egg, you only get one of the 4 is a viable egg. The polar bud is a product of division but their not viable, only one of the 4 is a viable egg cell unlikwin sperm where you get 4. polar body has chromo but not enough cytoplasm.
5 Stages of Prophase I
Leptotene -condensed chromosomes first visible
Zygotene -visible association of homologues (synapsis). Homo chromo pair up
Pachytene -end of synapsis. Fully paired
Diplotene -Dissolution of synaptonemal complex-chiasmata visible
Diakinesis - Meiotic spindle visible
Synaptonemal Complex
-helps to pair the chromo together.
-Two lateral protein elements
connected by transverse protein elements
Chiasmata
role in genetic enhance and help hold homo chromo together. Those will resolve into 2 homologes.
Separation of Homologous Chromosomes and Sister Chromatids
-Sister chromatids held together by cohesin
-Homologues held together by
chiasmata
-progress into anaphase 1, cohesion starts breaking down in the arms of the sis chromatids. Metapahse II they are still held together, then all the sites are arrested. The separated of the sis chromo can be triggered by the fertilization. Sperm head introduces prospholipase, it creates intercellular messenger called IP3 which opens up Ca stores. Ca influx and activation of APCcdc20 which destrypos cyclin B.
Oocyte arrested at metaphase II due to inhibition of APCCdc20. Fertilization leads to calcium influx and activation of APCCdc20 and destruction of cyclin B
2 Meiotic Nondisjunction
- Primary Nondisjunction
- Secondary Nondisjunction
- Antiploid, have an incorrect number of chromo’s.
- 20-25% are missing or 1 too many but these normally never make it past the early stage.
Primary Nondisjunction
The first option is primary nondisjunction which is where there’s an incorrect segregation of homologous chromosomes in the first meiotic division, resulting in some gametes with extra chromosome and some missing a chromosome.
Secondary Nondisjunction
Secondary nondisjunction is due to incorrect segregation of sister chromatids in the second meiotic division, where one will have an extra chromosome and the other will not.
Trisomy 21
Some of these abnormalities do survive. Down syndrome is an extra chromo 21. Chromo 21 is normal because it’s the smallest. extra copy of chromo means an extra dose of that genetic info. Effects other genes as well because that extra 21 has TF and there could be trans acting effects.
3 Abnormal Sex Chromosome Numbers
XO- Turner Syndrome- Female with genital development arrested and ovaries fail to develop
XXY- Klinefelter Syndrome- Male with presence of feminine physical characteristics
XYY- Physically normal male taller than average “Supermale”
