Cell Division Flashcards
What happens during Prophase I of meiosis?
Chromatin threads condense, coil and shorten into visible chromosomes.
Homologous chromosomes pair up. This is called synapsis.
One homologous chromosome comes from the male parent, the
other from the female parent.
Chromatids of homologous chromosome (HC) may cross
and twist around each other.
Point where they cross over is called a chiasma
Strength of coiling may cause them to break and exchange
parts (crossing over between non-sister chromatids of HC)
The centrioles move to opposite poles of the cell.
Nuclear envelope and nucleolus disintegrates.
Spindle fibres form.
What are features of homologous chromosomes?
Homologous chromosomes have the same
- shape
- length
- sequence of genes
- position of centromere
What happens during metaphase I?
Homologous chromosomes arrange themselves along the equator of the spindle.
Spindle fibres attach to centromere of each chromosome.
Arrangement of maternal and paternal chromosomes is random.
What happens during anaphase I?
Homologous chromosomes separate.
Spindle fibres shorten.
One of each pair of the homologous chromosomes is pulled to the opposite pole of the cell.
What happens during telophase ?
Spindle fibre disintegrates.
Nuclear envelope and nucleolus reforms at each poles (animal cells only).
Cytokinesis starts to occur, causing cleavage to appear within the cell.
What happens during prophase II?
Centrioles move to the opposite poles of the cell.
Spindle fibres appear.
Nuclear envelope and nucleolus disintegrates.
(SIMILAR TO MITOSIS PROPHASE)
What happens during metaphase II?
Chromosomes arrange themselves along the equator of the spindle.
Spindle fibre attaches to centromere of each chromosome.
What happens during anaphase II?
Spindle fibre shorten.
Centromeres divide.
Chromatids pulled to opposite poles of cell.
Once separated, chromatids with their own centromeres are
referred to as daughter chromosomes.
What happens during telophase II of meiosis?
chromosomes reach opposite poles of spindle.
chromosome uncoil, lengthen and become chromatin threads.
Spindle fibres disintegrates
Nuclear envelope & nucleolus reforms.
Why is meiosis important?
- Produces haploid gametes, which fuse together during fertilisation to produce diploid cells.
- Meiosis gives rise to genetic variation due to:
- crossing over of homologous chromosomes in prophase I
- independent assortment of homologous chromosomes at metaphase I (gametes can have different combinations of chromosomes).
3.
What happens during the interphase of cell division?
centrioles replicate & divide
The chromatin thread replicates to produce two genetically identical chromatin threads, joined at the centromere.
What happens during early prophase?
Chromatin threads condense, coil and shorten to form visible chromosomes.
Each chromosome consists of two sister chromatids attached at the centromere.
In animal cells, asters (made of microtubules) form around the centrioles.
Two pairs of centrioles move to opposite poles of cell.
Spindle fibres form extending from one pole of cell to the other.
Nucleolus disappears
Nuclear envelope disintegrates
What happens during the metaphase of mitosis?
Chromosomes line up singly along the equator of the spindle.
Chromosomes attached to spindle fibres at centromere.
What happens during anaphase?
Each centromeres divides
Spindle fibres shorten and pull chromatids apart to opposite poles of the cell (separation of sister chromatids)
• Each sister chromatid (with its own centromere) is now called a daughter chromosome.
What happens during telophase?
Chromosomes uncoil and becomes chromatin threads again.
Spindle fibres break down.
Nuclear envelope reforms around each set of chromosomes at the poles.
Nucleolus reforms in each nucleus.
