Level 2 Bio: Meiosis Flashcards
How many stages of Meiosis are there?
Two: Meiosis 1 and Meiosis 2
What is the purpose of Meiosis
The purpose of Meiosis is to produce gametes (sex cells: sperm, egg) which produces genetically different cells with haploid (1/2) the number of chromosomes
What is Meiosis
Cell division that halves the chromosome number so that each daughter cell has one haploid set.
It is Reduction division
Used to form gametes (sex cells (sperm & eggs in animals, pollen & eggs in plants))
What happens in Meiosis
In Meiosis the chromosomes are replicated once but the original cell undergoes 2 cell divisions.
How many daughter cells does Meiosis produce
4 genetically different daughter cells
What controls Meiosis
Enzymes
Do the sister chromatids separate in Meiosis, YES or NO?
NO
In prophase 1 what happens
Homologous chromosomes form a tetrad. When they pair up it’s called synapsis.
The arms of the chromosomes may tangle & form a chiasma.
In Metaphase 1 what happens
Tetrads line up along equator or middle of cell. Independent assortment takes place with Maternal & Paternal chromosomes.
In Anaphase 1 what happens
Centromeres break & homologous chromosomes separate (sister chromatids are still attached). Cytokinesis begins.
In Telophase 1 what happens
Chromosomes may decondense.
Meiosis 1 reaches completion.
In Prophase 2 what happens
Centrioles form & move toward the poles.
Nuclear membrane dissolves
In Metaphase 2 what happens
Microtubules grow from centrioles & attach to the centromeres.
The sister chromatids line up along the cell equator.
In Anaphase 2 what happens
Centromeres break & sister chromatids separate.
Cytokinesis begins.
In Telophase 2 what happens
Chromosomes may decondense (depends on species).
Cytokinesis reaches completion creating Haploid daughter cells.
This creates gametes
What is Step 1-Prophase 1
Step 1: Chromosomes have shortened & thickened, becoming clearly visible as two chromatids held together by a CENTROMERE. The group of four chromatids is called a TETRAD or a BIVALENT.
What is Step 2-Prophase 1
Step 2: Parts of adjacent chromatids can CROSS OVER & recombine.
What is Step 3-Metaphase 1
The chromosomes arrange themselves along the cell equator, with each member of a pair of homologous chromosomes orientated towards an opposite pole. SPINDLE fibres being pulling the homologous chromosomes apart.
After Step 3-Metaphase 1 the next stage of Meiosis (Anaphase 1) any combination of chromosomes from each of the homologous pairs can move towards the cell ______.
After Step 3-Metaphase 1 the next stage of Meiosis (Anaphase 1) any combination of chromosomes from each of the homologous pairs can move towards the cell POLES.
What is Step 4-Anaphase1
The homologous pairs separate & move towards the cell poles. The cell membrane begins to close up between them.
What is Step 5-Telophase 1
Two new cells form, both genetically unique because of the random assortment of alleles on the chromosomes that separated (& from crossing over) at Metaphase 1.
After Step 5-Telophase 1 the chromosomes can now undergo a resting time in which they unravel. Further shortening & thickening indicates the start of the second stage of divisions. This stage is known as _________ 2.
After Step 5-Telophase 1 the chromosomes can now undergo a resting time in which they unravel. Further shortening & thickening indicates the start of the second stage of divisions. This stage is known as PROPHASE 2.
What is Step 6-Metaphase 2
Chromosomes line up on the cell equator of each cell. Spindle fibres form. As in Metaphase 1, the positioning of chromosomes along the cell equator is random.
What is Step 7-Anaphase 2
Chromatids separate & move towards the cell poles. Cell membranes constrict between them.
What is Step 8-Telophase2
Four new haploid daughter cells have formed, each of different genetic makeup from the other. These cells are the gametes, & for them n=2 in this example.
At step 4, which member of which chromosome pair gets pulled into each new cell is random. At step 7, which _______ gets pulled into each new cell is random. This random assortment of chromosomes & _______, like the exchange of genetic material during step 2, & the different alleles present on each chromosome, increases the genetic variability of the __________ formed.
At step 4, which member of which chromosome pair gets pulled into each new cell is random. At step 7, which CHROMATID gets pulled into each new cell is random. This random assortment of chromosomes & CHROMATIDS, like the exchange of genetic material during step 2, & the different alleles present on each chromosome, increases the genetic variability of the GAMETES formed.
What process is a source of variation?
Meiosis
What 4 things happen during Meiosis
1) Segregation
2) Independent assortment
3) Crossing over
4) Linkage
What does Independent assortment do
Independent assortment influences on dihybrid inheritance.
What occurs during crossing over
During crossing over recombination of alleles occurs.
What does Linkage do
Linkage influences dihybrid inheritance
What are homologous chromosomes
Two matching chromosomes with same genes found in same loci (locus/location).
What are sister chromatids
1 half of a replicated chromosome
What is a centromere
The area when the sister chromatids are linked.
What is independent assortment & segregation
When homologous pairs line up in the middle of the cell, they line up randomly. This means that if you get your mum’s or dad’s chromosome from the homologous pair, it is completely random.
What is independent assortment a source of?
Independent assortment is a source of variation as each gamete can have any combination of chromosomes.
Meaning each gamete is unique & contains a different set of alleles to other gametes produced.
This means every offspring will also be unique.
What are the key differences & similarities between Meiosis & Mitosis
In Meiosis the sister chromatids don’t separate.
Meiosis creates genetically different cells & Mitosis creates genetically identical cells.
Enzymes control both processes .
Meiosis= Half number of chromosomes
Mitosis= Same number of chromosomes as parent cell (full number)
Meiosis= new combinations of alleles & chromosomes sort randomly of each other.
Mitosis= daughter cells are genetically identical.
What are the first two stages before Prophase 1
Interphase then DNA replication
