Cells and Genetic Material
Cells and Their Structure
- Cells are the basic building blocks of all living organisms.
- Each cell contains a nucleus, cytoplasm, and cell membrane.
- The nucleus controls the activities of the cell and contains chromosomes, which are made of DNA.
Chromosomes and Genes
- Chromosomes are long, coiled strands of DNA.
- Genes are sections of DNA that carry instructions for building an organism, including specific traits like hair colour or blood type.
- The human body has 23 pairs of chromosomes, totalling to 46.
DNA and Its Structure
- DNA (Deoxyribonucleic Acid) is a large molecule that contains all the genetic information for an organism.
- DNA is made up of two strands coiled into a double helix structure.
- Each strand consists of a sequence of four types of nucleotides: adenine (A), thymine (T), guanine (G), and cytosine (C).
- Adenine always pairs with thymine and guanine always pairs with cytosine, forming the 'rungs' of the DNA ladder.
Genetic Variation and Mutation
- Genetic variation arises from sexual reproduction, where chromosomes from two parents mix to produce offspring with unique combinations of genes.
- Mutations are changes in genes or chromosomes that can lead to new characteristics. These can be caused by errors in copying DNA during cell division, exposure to radiation, or exposure to certain chemicals.
- Some mutations can be beneficial and contribute to evolution, while others can lead to genetic disorders or diseases.
Genotype and Phenotype
- An organism’s genotype is the set of genes it carries, while its phenotype is its observable characteristics.
- The phenotype results from the interaction between the genotype and the environment.
Cell Division
- There are two types of cell division: mitosis and meiosis.
- Mitosis results in two identical daughter cells and is responsible for growth and repair in the body.
- Meiosis produces four non-identical daughter cells (gametes) used for sexual reproduction.
- During meiosis, the chromosomes pair up and exchange sections of DNA - this is known as "crossing over" and contributes to genetic variation.