Cell Division Flashcards
chromosomes are at their greatest
elongation (not visible)
- begin to coil, become more condensed
Prophase
nuclear membrane disappears
- spindle fibers : begin to appear
- chromosomes attach to the spindle fiber at their kinetochores.
Prometaphase
chromosomes attach to the spindle fiber
-surface of centromere
Kinetochores
Chromatin condenses into chromosomes
Nucleolus disappears
Prophase
mitotic spindle completed
-centrioles: divide and move to opposite poles
- chromosomes: line up on the equatorial plate,reach their maximum state of contraction.
Metaphase
centromeres: divide longitudinally
chromatids: separate and migrate to opposite poles
Anaphase
Chromosomes break at centromeres, and sister chromatids move to opposite ends of the cell
Anaphase
Chromosomes: uncoil, become
indistinguishable again.
Nucleoli: reform
Nuclear membrane: reconstructed
Followed by cytokinesis, or cytoplasmic division
Telophase
What appears during telophase
Cleavage furrow
takes place only in the ovaries and testes
Meiosis
Longest phase in meiosis
Prophase I
Complex stage that is further
subdivided into:
Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis
There are 46 chromosomes, each comprised of two chromatids.
Chromosomes begin to condense but are not visible by light microscopy.
Once takes place, the cell is committed to meiosis.
Leptotene
Homologous chromosomes (long threadlike structures) pair locus for locus. —- SYNAPSIS: paring locus for locus
A tripartite structure, the synaptonemal complex, can be seen in electron microscopy– necessary for the phenomenon of crossing-over that will takes place later in prophase I
Zygotene
crossing over of genetic material
-chromosome becomes short and thick and divide into four distinct chromatids.
Panchtene
Chromosomes continue to shorten and thicken
Homologous chromosomes begin to repel each
other
Repelling continues until the homologous chromosomes are held together only at points where crossing over took place
Diplotene
points where crossing over took place
Chiasmata
chromosomes reach their greatest contraction during this last stage of prophase.
Diakenesis
Disappearance of the nuclear membrane and formation of the mitotic spindle. The bivalents line up on the equatorial plate with their centromeres randomly oriented toward opposite poles
Metaphase 1
The centromeres of each bivalent separate and migrate to opposite poles.
Anaphase 1
Two haploid sets of chromosomes reach opposite poles and cytoplasm divides.
The result is two cells containing 23 chromosomes, each composed of two chromatids.
Telophase 1
Net result=4 cells each of which contains 23 chromosomes consisting a single chromatid.
Meiosis 2
Begins with sexual maturity and occurs throughout the post-pubertal life of a man.
Sprematogenesis
The spermatids differentiate to become
Spermatozoa
begins in prenatal life In females
Oogenesis
suspended diplotene is referred to
Dictyotene
How many potential four gametes produced each menstrual cycle is theoretically viable.
Only 1
The chromosomes of the egg and sperm produced in Meiosis II are each surrounded by a nuclear membrane within the cytoplasm of the ovum.
The pro-nuclei fuse to form the diploid nucleus of the zygote and the first mitotic division begins.
Fertilization
