RE 9.2 Cancer division and Cancer, Mitosis and Meiosis, Cellular process

Question 1

What types of mistakes can occur in double-stranded DNA replication?

Answer 1

Errors in DNA replication can include base substitutions, insertions, or deletions, which can lead to mutations in the DNA sequence.

Question 2

Explain the process of Mitosis

Answer 2

Interphase:
Interphase is the preparatory phase where the cell grows, duplicates its DNA, and prepares for division. During this phase, the chromosomes replicate, ensuring that each daughter cell will have a complete set of genetic material. Additionally, the cell undergoes growth and carries out normal metabolic activities to ensure it is ready for division.

Prophase:
Prophase marks the beginning of mitosis. During this stage, the chromatin condenses into visible chromosomes. The nuclear envelope dissolves, and the mitotic spindle begins to form.

Metaphase:
In metaphase, the chromosomes line up along the equator of the cell. Each chromosome is attached to microtubules from opposite poles of the cell, ensuring that they are properly aligned for separation.

Anaphase:
During anaphase, the sister chromatids of each chromosome separate and move to opposite poles of the cell. The microtubules shorten, pulling the chromatids toward the poles.

Telophase and Cytokinesis:
Telophase begins as the separated chromatids reach the opposite poles of the cell. The chromosomes begin to decondense, and nuclear envelopes form around them, marking the formation of two distinct nuclei. Meanwhile, cytokinesis occurs, where the cytoplasm divides, resulting in two daughter cells, each with a complete set of chromosomes identical to the parent cell.

Question 3

What happens in each stage of Meiosis I

Answer 3

nterphase:
Interphase is the preparatory phase where the cell grows, duplicates its DNA, and prepares for division. During this phase, the chromosomes replicate, ensuring that each daughter cell will have a complete set of genetic material. Additionally, the cell undergoes growth and carries out normal metabolic activities to ensure it is ready for division.

Prophase I:
Prophase I marks the beginning of meiosis. During this stage, homologous chromosomes pair up and form tetrads. Crossing over occurs, where sections of chromatids are exchanged between homologous chromosomes. This genetic exchange increases genetic diversity among the resulting daughter cells.

Metaphase I:
In metaphase I, the paired homologous chromosomes line up along the equator of the cell. The orientation of each pair is random, contributing further to genetic variation.

Anaphase I:
During anaphase I, homologous chromosomes separate and move to opposite poles of the cell. Each pole receives one chromosome from each homologous pair, ensuring that the resulting daughter cells will have a complete set of chromosomes, but with genetic variation due to crossing over.

Telophase I and Cytokinesis:
Telophase I marks the end of the first division of meiosis. Chromosomes reach opposite poles of the cell, and a nuclear membrane forms around each set of chromosomes. The cell then undergoes cytokinesis, where the cytoplasm divides, resulting in two daughter cells, each with half the number of chromosomes as the original cell.

Question 4

What happens in Meiosis II

Answer 4

Interphase II:
Interphase II is a shorter phase where the two daughter cells from meiosis I prepare for the second division. There is no DNA replication during this phase.

Prophase II:
Prophase II initiates the second division of meiosis. Chromosomes condense again, and a new spindle apparatus forms. However, unlike prophase I, there is no pairing of homologous chromosomes or crossing over during this phase.

Metaphase II:
In metaphase II, the chromosomes line up along the equator of each daughter cell. This time, they are single chromosomes, as opposed to homologous pairs.

Anaphase II:
During anaphase II, the sister chromatids of each chromosome separate and move to opposite poles of the cell.
Telophase II and Cytokinesis:
Telophase II marks the end of meiosis. Chromosomes reach opposite poles of the cell, and nuclear envelopes form around them. The cell then undergoes cytokinesis once again, resulting in four haploid daughter cells, each with a unique combination of genetic material due to crossing over and random assortment during meiosis I and II.