Where does mitosis occur

Meiosis and mitosis


Terms: homologous chromosomes: chromosomes of a pair (a pair of mother and father each) chromosomes: carrier of genetic information

haploid chromosome set: simple chromosome set in sex cells diploid chromosome set: in body cells the nuclei contain 2 chromosome sets (each chromosome has 2 chromosomes)


- Processes that lead to a new and redistribution of the genetic makeup (formation of new gene combinations) -> important basis of genetic variability
- occurs through distribution of chromosomes during mitosis, meiosis and during fertilization (interchromosomal R.)
- also takes place through the exchange of chromosome fragments and thus the exchange of genes through crossing over (intrachromosomal R.) ---> Chiasmata: connection points of homologous chromosomes at the points of crossing over
- Example: - Cell with 6 chromosomes (3 from the father and 3 from the mother) ---> various genetic information
- through interchromosomal recombination 8 (2³) different germ cells can arise (differentiation in allele composition) ---> formation of the zygote from egg and sperm cell = 64 possibilities

Comparison between mitosis <----> meiosis:

- Cell type (body cells + asexual reproduction <----> formation of germ cells and in the case of sexual reproduction)
- Result (2 identical cells with diploid chromosome set <----> 4 different cells with haploid chromosome set)
- Anaphase (divided chromosomes are drawn to the cell poles <---> whole chromosomes are drawn there)

Course of mitosis:

Def .: Form of nucleus and cell division in which genetically identical cells arise. An even distribution of the genetic make-up on the

Daughter cells are guaranteed. Occurs in the formation of all body cells and in asexual reproduction.

Result: Two identical cells with a diploid set of chromosomes emerge from one diploid cell

1. Prophase:

- Chromosomes become visible
- they spiral to form the form of transport
- two chromatids are visible
- Spindle fibers are formed
- Nuclear membrane dissolves

2nd metaphase:

- Chromosomes shortened to the maximum
- Chromatids easily recognizable (two chromatid chromosomes)
- Arrangement in the equatorial plane
- Centromeres and cell poles connected by spindle fibers

3. Anaphase:

- Centromeres divide
- Chromatids diverge and migrate to the cell poles

4. Telophase:

- Chromosomes (single chromatid chromosomes) unwind
- Cell membrane forms
- new nuclear membrane is formed

Interphase -> phase between 2 mitoses: - G1: growth phase; Daughter cells become mother cells

S: synthesis phase; Duplication of DNA G2: further growth phase

S0: resting stage

Course of meiosis:

Def .: Form of nucleus and cell division in which genetically unequal daughter cells with a haploid set of chromosomes arise. It occurs during the formation of germ cells and during sexual reproduction.

Result: 4 haploid sperm cells develop from a diploid cell in the male sex, a haploid egg cell and 3 haploid polar bodies in the female sex. Starting point: fertilization between male and female. Gender ---> Creation of a zygote (fertilized egg cell) with a diploid set of chromosomes


1. Prophase:

- Chromatids become visible
- Chromosomes spiral to form the form of transport
- Spindle fibers are formed
- Nuclear envelope dissolves
- homologous chromosomes arrange themselves (tetrad)

2nd metaphase:

- Chromosomes shortened to the maximum (two-chromatid chromosomes)
- Arrangement in the equatorial plane
- Spindle fibers formed
- random arrangement of homologous chromosomes
- both recombinations

3. Anaphase:

- One homologous chromosome each (whole two-chromatid chromosome) migrates to the poles
- each daughter cell receives a haploid chromosome set

4. Telophase: - Two-chromatid chromosomes reach the cell poles


- in a normal -> mitosis the chromatids of the homologous chromosomes are separated
- new nuclear membranes and cell membranes are formed

Change in shape of the chromosome during the cell cycle

1. DNA double helix -> actually wrong but
2nd string of pearls - chromatin ---> DNA strand is wound around a histone 1.5 - 2 times (= nucleoson)
3. Chromatin fiber from packed nucleosomes -> form of transport in the metaphase