Mitosis and meiosis

Question 1

Type of chromosomes depending on their centromere

Answer 1

Metacentric (middle)
Submetacentric (above middle)
Acrocentric (close to end)
Telocentric (end)

Question 2

Cell cycle

Answer 2

Interphase: cell growth
- G1 growth
- G0 if dormant
- S synthesis of DNA: 2n chromosomes, 4n molecules kept together by choesin
- G2: mitosis preparation
Mitosis

Question 3

Mitosis

Answer 3

• Prophase: DNA condensation in 2n dichromatidic chromosomes, centrioles migrate to cell poles
• Prometaphase: nuclear membrane dissolves, spindle fibers made of tubulin attach to kinetochore (proteins on the chromosomes’ centromere)
• Metaphase: spindle fibers align all chromosomes on the metaphasic plane
• Anaphase: choesins dissolve, spindle fibers separate sister chromatids and move them to the cell poles
• Telophase: the two new nuclear membranes form, one enveloping each of the 2n monochromatidic chromosomes
• Cytokinesis

Question 4

Possible combinations of independent assortment

Answer 4

2ⁿ

Question 5

Crossing-over

Answer 5

In Prophase I of mitosis, homologous dichromatidic chromosomes form tetrads (couples of dichromatidic chromosomes, bivalent formings). This happens thanks to the synaptonemal complexes and the synapsis. An exchange between non-sister chromatids happens and those points of exchange are called chiasma.

Question 6

Meiosis

Answer 6

Meiosis I (reductional):
- Prophase I: dichromatidic chromosomes condensation, tedrads, crossing-over, dissociation of synaptonemal complexes, nuclear membrane disappears
- Metaphase I: the tetrads align on the metaphasic plate
- Anaphase I: homologous dichromatidic chromosomes are separated
- Telophase I: two new membranes form around the two new nuclei with n dichromatidic chromosomes
Meiosis II (equational): like mitosis.