Introduction to Mitosis

Growth, inheritance, and reproduction depend on cell division. In this lecture we will begin a discussion of what instructions are necessary for inheritance, and how those instructions are duplicated for distribution into the daughter cells that are created when a cell divides. We will also discuss the mechanisms by which those instructions are divided into daughter cells.

In cell division, parent cells must provide their daughter cells with hereditary instructions that are encoded in DNA and with enough cytoplasmic machinery to start up their own operation.

Before a cell of an organism reproduces, it undergoes mitosis or meiosis. Both are nuclear division mechanisms that sort out the parent's DNA into new nuclei followed by a mechanism that divides the cytoplasm into daughter cells.

In this lecture, we will cover how multicelled organisms grow by way of mitosis of the body cells (also called somatic cells). When a cell undergoes mitosis, the daughter cells have identical genes and the daughter cell has genes identical to those of the mother cell that produced it.

We will also cover meiosis which occurs in germ cells. Germ cells generate gametes (e.g. eggs and sperm) necessary for sexual reproduction.

Chromosomes

Chromosomes are molecules of DNA complexed with proteins.

Between divisions, each threadlike chromosome is duplicated to form sister chromatids joined by a centromere . The centromere is the region where the chromosome will attach to microtubules during nuclear division. The area where both chromatids are in contact with each other is known as the centromere. Kinetochores are on the outer sides of the centromere.

The DNA of humans and other eukaryotes is highly organized to prevent tangling. A type of protein called histones act as spools to wind the DNA into units called nucleosomes. Another histone stabilizes the arrangement and allows the beaded chain to form looped regions.

The Number of Chromosomes: All somatic cells of a particular species have the same number of chromosomes. For example, humans have forty-six chromosomes.

• Chromosomes come in pairs-one member from each parent.
• Chromosome pairs carry genes for the same traits.

Diploid vs Haploid: Chromosome number (n) tells how many of each type of chromosome is present in a cell:

• 2n is diploid.
• n is haploid.

This animation (Audio - Important) describes how a chromosome is organized.

REVIEW: When a cell undergoes mitosis the daughter cells have identical genes
Answer and the daughter cell has genes identical to those of the mother cell that produced it.