Nuclear Division

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Cells are able to grow and reproduce. Cells reproduce by splitting and passing on their genes (hereditary information) to Daughter cells. The nucleus always divides before the rest of the cell divides. Therefore each daughter cell contains their own nucleus. The nucleus controls the cells activities through the genetic material DNA. The cells in a body are all the same except the gametes they were all made from one cell, the Zygote. This is the cell that was formed when two gametes from your parents fused.

A Karyotype is when you cut out individual chromosomes from a picture and rearrange them. There are matching pairs of chromosomes these are called homologous pairs. Each pair is given a number. One of each pair came from the mother and one of each pair came from the father. The pairs can be distinguished as each pair has a distinctive banding pattern when stained. There are two sex chromosomes and the rest are called autosomes. In most karyotype the sex cells are kept to one side so that the sex can be seen easily. In females they have two X chromosomes and in the males they have an X and a Y chromosome. The Y chromosome has a portion missing and is therefore smaller then the X chromosome.

Each chromosome has a characteristic set of genes, which code for different features. The human Genome project is investigating which genes are located on which chromosomes. The gene for cystic fibrosis is located on chromosome 7.

Cells that contain two sets on chromosomes are called diploid. This is represented as 2n, n=number of chromosomes in one set of chromosomes. Cells that contain one set of chromosomes is called haploid. This is represented as n.

Structure of Chromosomes

A chromosome is made up of two identical structures called chromatids. The process of nuclear division is called interphase; each DNA molecule in a nucleus makes an identical copy of itself. Each copy is contained in the chromatid and a characteristic narrow region called the centromere holds the two chromatids together. The centromere can be found anywhere along a chromosome but the position is the characteristic for a particular chromosome. Each Chromatid contains one DNA molecule. DNA is the molecule of inheritance and is made up of a series of genes. The fact that the two DNA molecules in the sister chromatids, and hence their genes, are identical is the key to precise nuclear division.

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