Untitled Quiz

Each chromosome is made up of duplicate chromatids joined at their centromeres.
During prophase, the two centriole pairs begin to separate and move towards opposite poles of the cell.
- Microtubules are assembled between the centriole pairs to form the mitotic spindle.
- Other microtubules radiate to form the asters which lie at the spindle poles.
- The nucleoli disappear, and the nuclear membrane disintegrates.
Prometaphase:
- The spindle microtubules extend into the central region of the cell and attach to the chromosomes which move towards the equator of the spindle.

The plane where the chromosomes align is called the metaphase or equatorial plate.
Chromosomes attached at their centromeres are arranged in a ring when observed from the poles of the cell or appear linearly across the plane when viewed from above.

The centromere in metaphase is a double structure (one per sister chromatid).
During anaphase, the centromere halves separate, carrying an attached chromatid.
Each original chromosome splits lengthwise into two new chromosomes, which move apart towards opposite poles.
At the end of anaphase, the chromosomes are grouped at each end of the cell, creating two diploid clusters.

The chromosomes decondense.
A nuclear membrane forms from membranous vesicles at the chromosome ends.
Nucleoli appear.
Cytoplasmic division, which began in early anaphase, continues until new cells separate, each with its own nucleus.

The spindle remnant disintegrates.
A peripheral band of actin and myosin appears in the constricting zone, responsible for furrow formation.

Failure of chromatids to separate, resulting in paired chromatids going to the same pole, may sometimes occur.
One cell will have more, and the other will have fewer chromosomes than the diploid number.
Exposure to ionizing radiation can promote non-disjunction and inhibit mitosis.
Many cytotoxic drugs used in cancer therapy inhibit the formation of spindle microtubules, arresting mitosis in metaphase.

Two cell divisions occur during meiosis: Meiosis I and Meiosis II.
The process differs at the cellular level for male and female lineages.
Meiosis involves one replication of chromosomes followed by two consecutive cell divisions.
A diploid cell produces four haploid germ cells (gametes).
Crossing over occurs in meiosis, rearranging alleles to ensure genetic diversity in gametes.

Before meiosis starts, chromosomes are duplicated (meiotic S phase).
Crossing over of chromatids occurs, exchanging genetic information between homologous chromosomes.
This process mixes up paternally and maternally derived alleles, creating unique haploid gametes.

Resembles mitotic metaphase; however, the bodies attaching to the spindle microtubules are bivalents, not single chromosomes.
Homologous pairs lie parallel to the equatorial plate, with one on either side.

Chiasmata disappear.
Entire homologous chromosomes, not paired chromatids, move to opposite poles, leading to random assortment of maternal and paternal chromosomes.

Occurs shortly after Meiosis I without any DNA synthesis.
Similar to mitosis, chromatids separate during anaphase, but in contrast to mitosis, the separating chromatids are genetically different.

A rapid, regulated cellular process that eliminates defective or unneeded cells by shrinking and eliminating them.
Results in small, membrane-enclosed apoptotic bodies, phagocytized by neighboring cells.
Apoptosis avoids the release of cellular components that trigger an inflammatory response, unlike necrosis, which is caused by injury.

Bcl-2 family proteins regulate the release of death-promoting factors from mitochondria.
Activated by external signals or irreversible internal damage, specific Bcl-2 proteins induce a process with the following features:
- Loss of mitochondrial function and caspase activation: Bcl-2 proteins compromise the mitochondrial membrane, releasing cytochrome c into the cytoplasm, activating caspase proteolytic enzymes.
- Fragmentation of DNA: Endonucleases cleave DNA into small fragments, enabling histochemical staining of apoptotic cells.
- Shrinkage of nuclear and cell volumes: The cell quickly shrinks due to the destruction of cytoskeleton and chromatin, resulting in dense, darkly stained pyknotic nuclei.
- Cell membrane changes: The cell membrane undergoes blebbing and shape changes due to protein degradation and lipid mobility.
- Formation and phagocytic removal: Membrane-bound remnants of cytoplasm and nucleus separate as apoptotic bodies and are phagocytized by neighboring cells.

Retinoblastoma, a cancer occurring in the eyes of young children, is linked to deactivated genes that control apoptosis, allowing cancer cell progression.
Failure of clonal deletion, a process that eliminates self-reactive immune cells, can lead to autoimmune disorders.
Karyotyping (examination of chromosomes in dividing cells) provides diagnostic information about the chromosomal complement of individuals or malignant tumors.