Mitosis, Meiosis and Non-Disjunction (LEC)

What are the stages of the cell cycle?

G1, G0, S, G2, and M.

What occurs during G1 phase?

Cell size increases, protein synthesis is active, cells differentiate and perform their functions, and check if they are ready for division.

What is the purpose of the G0 phase?

Cells can perform functions but are unable to divide; permanent and stable cells are in G0, while stable cells can reenter the cell cycle with stimuli.

What happens during the S phase?

DNA replication occurs, doubling the DNA content to form two sister chromatids per chromosome.

Describe the events of the G2 phase.

The cell size increases, DNA content is double, the genome is scanned for mistakes, and DNA repair mechanisms are activated.

What events occur during the M phase of the cell cycle?

Includes Prophase (nuclear envelope dissolves, spindle forms), Metaphase (chromosomes align), Anaphase (sister chromatids separate), and Telophase (nuclear envelope reforms, cytokinesis).

What is the role of p53 in the cell cycle?

p53 is involved in genome surveillance, can induce cell cycle arrest, activates DNA repair, and prompts apoptosis if damage is extensive.

Describe the chromosomal structure in G1 and G0 phases.

One chromatid per chromosome (2n;2d).

What characterizes the chromosomal structure during the S phase?

Two sister chromatids per chromosome (2n;4d).

What are the main achievements of meiosis?

Formation of haploid gametes, genetic recombination, and increased genetic diversity.

Summarize the events of meiosis I and meiosis II.

Meiosis I: homologous chromosomes separate; Meiosis II: sister chromatids separate.

What is the outcome of nondisjunction during meiosis I for Turner and Klinefelter syndromes?

Meiosis I: 45X leads to Turner syndrome; 47XXY leads to Klinefelter syndrome.

What happens during prophase I of meiosis and why is it significant?

Recombination occurs leading to the greatest genetic diversity.

How does meiosis contribute to gametogenesis?

Meiosis produces haploid gametes and is responsible for genetic diversity via recombination.

Compare the outcomes of nondisjunction in meiosis and mitosis.

Nondisjunction can lead to disorders like Turner (45X), Klinefelter (47XXY), XYY (47XYY), or XXX (47XXX) syndromes.

What are the distinguishing features of metacentric, submetacentric, acrocentric, and telocentric chromosomes?

Metacentric: equal arms; Submetacentric: shorter p arm; Acrocentric: p arm minimal; Telocentric: centromere at the end.

Outline differences between meiosis in males and females.

Meiosis in males results in four functional sperm whereas in females, it creates one functional egg and three polar bodies.