At the beginning of the first mitotic stage, prophase, the thread-like doubled chromosomes contract and become visible. The two centrioles move to opposite sides of the nucleus. At the same time, the nuclear membrane begins to break down.

After the pairs of chromosomes are aligned, anaphase I begins. During this stage, the microtubules, or spindle fibers, pull the homologous chromosomes apart and move them to opposite ends of the cell.

chromosome duplication …of a set of duplicate chromatids that are held together by the centromere. The centromere is the point of attachment of the kinetochore, a protein structure that is connected to the spindle fibres (part of a structure that pulls the chromatids to opposite ends of the cell).

When nondisjunction occurs in meiosis II, cells divide normally during anaphase I (homologous chromosomes separate correctly), but sister chromatids fail to separate during anaphase II (as seen in the diagram above, on the left). This again results in four possible haploid gametes.

Sometimes during anaphase, chromosomes will fail to separate properly. This is called nondisjunction. Nondisjunction results in cells with abnormal numbers of chromosomes. Instead, one pair of sister chromatids failed to split, resulting in one cell with 5 chromosomes and one cell with 3 chromosomes.

In cell division, after replication of the cell’s chromosomes, the two copies, called sister chromatids, must be kept together to ensure that each daughter cell receives an equal complement of chromosomes. In higher organisms, DNA is packaged into chromosomes.

Duplicate the chromosome for DNA duplication (S synthesis)  What color should the sister chromatids be for each pair? Yellow and red 4.

Sister chromatids are two identical copies of a chromatid. When we say “identical,” they are exact replicas of the parent chromatid. Sister chromatids have the same genes and the same alleles. Non-sister chromatids are also called as homologues.

Sister chromatids are by and large identical (since they carry the same alleles, also called variants or versions, of genes) because they derive from one original chromosome. Homologous chromosomes might or might not be the same as each other because they derive from different parents.

Anaphase II is the stage when sister chromatids of every chromosome separate and begin to move towards the opposite ends of the cell. The separation and the movement is due to the shortening of the kinetochore microtubules.

The sister chromatids are identical to one another and are attached to each other by proteins called cohesins. The attachment between sister chromatids is tightest at the centromere, a region of DNA that is important for their separation during later stages of cell division.

maternal lineage

anaphase

one sister

How do daughter cells obtain their DNA? The DNA in the parent cell nucleus makes a copy of itself and is then split between the two daughter cells during mitosis. The cell grows and makes a copy of its genetic material.

Prophase: the nuclear envelope breaks down, chromosomes condense, and spindle fibers connect to sister chromatids. Metaphase: spindle fibers pull sister chromatids to the metaphase plate at the equator of the cell. Anaphase: spindle fibers separate sister chromatids to opposite poles of the cell.