cell division (Cbol)

Define the cell cycle

The process by which cells copy their DNA and divide to produce genetically identical ‘daughter’ cells

Heterochromatin

the regions that stain darkly on the chromosomes

what is the g0 phase and whats its function?

An optional, non-replicative phase of the cell cycle. Many differentiated cells, like liver cells (hepatocytes), remain in this state. A cell in G0/G1 is considered to be in its normal state.

what is the g1 phase?

A period of cell growth and preparation for cell division. Important components for division, such as centrosomes, are replicated during this phase

what is the s phase?

The synthesis phase where DNA replication occurs. The cell's DNA is copied. After this phase, each chromosome consists of two sister chromatids. The DNA content doubles, which is sometimes represented as going from '2n' to '4n'

what is the g2 phase?

short resting phase between DNA synthesis (S phase) and cell division (M phase). It is the gap between the S phase and Mitosis

what is the m (mitosis) phase and whats its function?

The cell division phase of the cell cycle The copied DNA is accurately divided, so that the two daughter cells each receive a full copy of every chromosome. Mitosis itself has several stages (Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis) PMAT

what is the interphase?

The collective name for the G1, S, and G2 phases

What is the main purpose and outcome of Mitosis?

Mitosis is a type of cell division that occurs in somatic (body) cells. it produces two genetically identical diploid (2n) daughter cells from a single parent cell. Each daughter cell receives a full copy of every chromosome.

What is the overall mechanism of Mitosis?

Mitosis involves one round of DNA replication followed by one round of cell division.

1. DNA Replication (S Phase): The DNA is copied once, so each of the 46 chromosomes is made of two identical sister chromatids held together at a centromere.

2. Cell Division: The cell divides once, separating the sister chromatids.

What happens during Prophase?

Chromosomes condense and become visible, Bipolar spindle develops

what happens during prometaphase?

Nuclear envelope dissolves, chromosomes begin to migrate to the equatorial plane (metaphase plate) and are seen to contain 2 chromatids

what happens during metaphase?

Chromosomes fully condensed and located at metaphase plate

what happens during anaphase?

each centromere splits. The two chromatids of each chromosome pair are pulled to opposite poles

what happens during telophase?

Chromosomes reach poles and start to decondense, Nuclear membrane reforms, Cytoplasm starts to divide

what happens during cytokinesis

Cytoplasm division completed to give two identical daughter cells

where does mitosis occur?

In somatic cells and it produces diploid cells.

what is a diploid cell?

2 copies of the chromosome set 2n

where does meiosis occur?

during reproduction and it produces gametes in the form of a haploid. The diploid status is restored during fertilisation.

what is a haploid?

1 copy of chromosome set n

what happens at meiosis 1 prophase?

• Chromosomes condense, spindle forms.

• Homologous chromosomes pair (maternal + paternal) → form bivalents/tetrads.

• Crossing over (recombination) occurs at chiasmata → exchange of genetic material.

• Outcome: new combinations of alleles created

what happens at meiosis 1 metaphase?

• Bivalents align at the metaphase plate.

• Independent assortment: paternal and maternal homologs line up randomly.

• Outcome: huge genetic variation

what happens at meiosis 1 anaphase?

• Homologous chromosomes (each still with 2 chromatids) separate to opposite poles.

• Outcome: chromosome number is halved.

what happens at meiosis 1 telophase and cytokinesis?

• Nuclear envelope may reform briefly.

• Cytoplasm divides into 2 cells.

• Outcome: 2 haploid cells, each with 23 chromosomes (in humans), but each chromosome still has two chromatids.

What are the two mechanisms to produce genetic variation?

Recombination and independent assortment.

Explain recombination.

• Occurs in Prophase I when homologous chromosomes pair to form a bivalent (tetrad).

• At points called chiasmata, the DNA of a maternal chromatid physically breaks and rejoins with a paternal chromatid.

• This results in exchange of DNA sequences between maternal and paternal homologues.

• Normally, recombination is precise no DNA is gained or lost.

• If errors occur (like nondisjunction or faulty crossover), it can lead to chromosome abnormalities (e.g. Down syndrome).

explain independent assortment.

• Happens in Metaphase I when homologous pairs of chromosomes (bivalents) line up at the metaphase plate.

• Each pair aligns randomly with respect to maternal or paternal orientation.

• The spindle then pulls one of the homologues to each pole random choice of maternal vs paternal chromosome for each pair.

Define allele

A version of a gene found at a specific location (locus) on a chromosome.

define genotype

The genetic makeup of an organism the specific alleles an individual carries.

define phenotype

The observable traits or characteristics of an organism, resulting from the genotype

define homozygote

An individual with two identical alleles for a gene.

define heterozygote

An individual with two different alleles for a gene.