Lecture 12 - Mitosis and Meiosis : Simon Whitehall Flashcards
What are the 5 stages of Mitosis?
Prophase Prometaphase Metaphase Anaphase Telophase
What is the G0 state?
A non dividing senescent state.
What is a kinetochore?
Protein structure located at the centromere that serves as attachment point for mitotic spindles.
What is a centriole?
Cytoplasmic organelle composed of 9 groups of microtubules that act as foci for creating mitotic spindle fibres.
What is a centrosome?
Region of cytoplasm containing pair of centrioles.
What is a centromere?
The centre of the chromosome, where the 2 sister chromatids join.
What happens in G2 of interphase?
Chromosomes extend
What happens during Prophase?
Chromosomes condense and the centrioles divide and move apart.
What happens during prometaphase?
Centrioles reach the opposite poles.
Spindle fibres form and attach to the kinetochore.
What happens during metaphase?
Centromeres align on the metaphase plate along the midline of the cell., nuclear envelope breaks down.
What happens during anaphase?
Centromeres split (once all have lined up on the spindle) and daughter chromosomes migrate to opposite poles as they are pulled by the mitotic spindles.
What happens during Telophase/Cytokinesis?
Daughter chromosomes arrive at poles.
Chromosome de-condenses
Nuclear envelope reforms
Cell division occurs.
What is a chiasma?
A physical connection between non sister chromatids. This leads to crossing over.
What are the sub-stages of Prophase I?
Leptonema Zygonema Pachynema Diplonema Diakinesis
What happens during Leptotene?
Duplicated chromosomes start to condense.
What happens during Zygotene?
Synapsis begins, the chromosomes start to join (bivalent forming)
What happens during Pachytene?
Synapsis is complete, and crossing over occurs.
What happens during Diplotene?
Synaptonemal complex disappears, and the chiasma is visible.
What happens during Diakinesis?
Nuclear envelope fragments, and the bivalent chromosomes are ready for metaphase.
What is the synaptonemal complex?
A nucleoprotein zipper that forms between the paired homologous chromosomes. It looks like a backbone with lateral elements with chromatin attached to the sides.
It plays an important role in crossing over, and suggests an important role in the formation of chiasmata.
What is the metaphase plate?
Where all the chromosomes line up on the horizontal axis.
What are asters?
Very short microtubules.
_______ do not act independently in Meiosis.
Non-Sister chromatids.
What does Bivalent/Tetrad mean?
2 pairs of non sister chromatids joined together.
What is a dyad?
One half of the tetrad.
What can happen , and what will not happen between Meiosis I and Meiosis II?
There can be a short interphase, but no DNA replication and no chiasmata formation or crossing over.
What is the pathway for the development of gametes in a male?
Spermatogonium -> Growth Primary spermatocyte -> Meiosis I 2 secondary Spermatocytes ->Meiosis II 4 Spermatids -> Differentiation 4 Spermatazoa
What is the pathway for development of gametes in a female?
Oogonium -> Growth Primary oocyte -> Meiosis I Secondary Oocyte + polar body -> Meiosis II *of 2ndry oocyte* Oootid -> Differentiation Ovum
What happens during meiosis in a female?
During development 1st oocyte division takes place but pauses at prophase I.
Meiosis resumes many years later (prior to ovulation) and 2nd division only completed after fertilization.
What is Aneuploidy, and how does it develop?
Chromosome number is not an exact multiple of the haploid number. Nondisjunction results in aneuploid gametes.
What is Trisomy?
3 copies of a particular chromosome.
Where do Meiosis and Mitosis occur?
Meiosis occurs in a diploid cell
Mitosis can occur in haploid and diploid cells.
Where does meiosis take place in higher eukaryotes?
Testis and Ovary
What are some human syndromes associated with trisomies?
Down Syndrome Edwards Syndrome Warkany Syndrome 2 Patau Syndrome Chronic Lymphocytic Leukaemia
How do you calculate no. of variations of gametes diploid organisms can produce?
2^number of homologous chromosomes.
