Meiosis
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2 complete sets of genes are found in most adult organisms
Homologous- ​each of the 4 chromosomes from male parent has a corresponding chromosome
from female parent
Diploid Cells- ​holds both sets of homologous chromosomes; shown as 2N; somatic cells
Haploid Cells-​ holds only one set of homologous chromosomes; shown as N; sex cell
Zygote- ​ a fertile egg
Acquired Characteristic- ​characteristic one receives after they are born; may be due to
environment, a disease, injury, etc…
Inherited Characteristic- ​characteristic one receives from the genes of the parent; eye color,
heright, hair color, etc...
Phase of Meiosis
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Meiosis is a process by which the number of chromosomes per cell is cut in half
Produces the gametes, which are sex cells
2 distinct divisions
Stant out with diploid cells (2N) and at the end of the second division, there will be 4
haploid cells (N)
Meiosis I
1. Prophase I- ​crossing over occurs which provides genetic variation; this forms a Tetrad,
which is 4 chromatids; homologous chromosomes paired together
2. Metaphase I- ​the paired homologous chromosomes line up in the middle
3. Anaphase I- ​the paired homologous chromosomes are pulled apart
4. Telophase I and Cytokinesis-​ 2 new cells are reproduced and they are still diploid cells
(2N)
Meiosis II
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Prophase- ​ in Meiosis II there is no prophase
Metaphase II- ​homologous chromosomes line up in the middle
Anaphase II- ​the paired chromatids separate
Telophase II and Cytokinesis- ​4 new haploid cells are formed. They have half the
number of chromosomes compared to the original cell at the beginning of Meiosis I
Comparing Meiosis and Mitosis
Replication and Separation of Genetic Material
- Mitosis produces exact copies; clones
- Meiosis has half the number of chromosomes
Changes in Chromosome Number
- Mitosis has the same number of chromosomes at the end
- Meiosis has half the number of chromosomes
Number of Cell Divisions
- Mitosis is a single cell division so they are genetically identical
- Meiosis is two rounds of cell division that produce 4 genetically different cells
Step by step process
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Cell undergoes DNA replication
Crossing over occurs
Homologous chromosomes line up in the middle
Spindle attach
Spindle pull homologous pairs apart
2 daughter cells
Sister chromatids separate from each other
Individual chromatids move to end of cell
4 haploid cells