This page delves into more complex terms and processes related to cell division, chromosomal behavior, and genetic variation. It covers important structures and events that occur during mitosis and meiosis.

Definition: Gametes are reproductive cells, such as sperm and egg cells, while somatic cells are any body cells that are not germ cells (reproductive cells).

Key structures and concepts:

• Spindle fibres: Protein structures that move chromosomes to opposite poles during cell division
• Centrioles: Structures in the cytoplasm where spindle fibres form, part of the cytoskeleton
• Chromatids: One half of a replicated chromosome, joined to the other half at the centromere
• Sister chromatids: Two identical copies of a parent chromosome attached at the centromere

Highlight: Replicated chromosomes contain two identical sister chromatids, while unreplicated chromosomes consist of only one double strand.

Genetic terms and processes:

• Allele: One variant of a particular gene, e.g., for eye color
• Gene: A section of a chromosome that codes for a product (protein or RNA)
• Homologous chromosomes: Chromosomes that are identical in terms of size, shape, banding pattern, and array of genes

Vocabulary: A bivalent chromosome is one pair of chromosomes (sister chromatids) in a tetrad, formed in prophase I of meiosis.

Important processes in genetic variation:

1. Independent assortment: The process in metaphase I where alleles of genes swap into different chromosomes, resulting in unique chromosome combinations
2. Crossing over: The exchange of DNA sections between homologous chromosomes, taking place in prophase I of meiosis

Example: Crossing over and independent assortment contribute to genetic diversity in offspring, which is crucial for evolution and adaptation.

These advanced concepts build upon the basic understanding of mitosis and cell division, providing a comprehensive view of the complex processes involved in cellular reproduction and genetic inheritance.

This page provides essential definitions and explanations for understanding mitosis and DNA-related terms in cell division. It covers the fundamental processes and structures involved in the cell cycle and mitotic division.

Definition: Mitosis is the process of cell division in which daughter cells are genetically identical to each other and the mother cell.

Vocabulary: The cell cycle is the progression of a parent cell from growth and development, through DNA synthesis, to cell division, producing daughter cells.

The cell cycle consists of interphase and mitosis. Interphase is divided into three stages:

1. G₁ phase: Cell growth and development
2. S phase: DNA replication
3. G₂ phase: Organelle replication and protein synthesis

Highlight: During the S phase, DNA synthesis occurs. The two strands of the DNA double helix separate, each serving as a template for the synthesis of a complementary daughter strand.

Key structures involved in mitosis include:

• Chromosomes: Structures in eukaryotic nuclei, contained in two helices when replicated and one when unreplicated
• DNA double helix: The structure of genetic material, consisting of two complementary strands that twist around each other like a spiral
• Chromatin: The substance within a chromosome, consisting of DNA and protein

Example: In human somatic cells, which are diploid, there are 46 chromosomes arranged in 23 pairs.

The stages of mitosis are:

1. Prophase: Replicated chromosomes condense, the nuclear envelope disappears, and centrioles migrate
2. Metaphase: Replicated chromosomes align at the cell's equator
3. Anaphase: Sister chromatids separate, and daughter chromosomes migrate to opposite poles
4. Telophase: The nuclear envelope reforms, and spindle fibres disappear, resulting in two genetically identical daughter cells

Vocabulary: Cytokinesis is the division of the cytoplasm at the end of nuclear division, completing the formation of two separate daughter cells.