Genetics and Reproduction in Biology
Reproduction (B1 3):
Types of Reproduction
Reproduction involves passing genetic information in the chromosomes onto offspring. There are two types of reproduction: asexual reproduction and sexual reproduction. Asexual reproduction does not involve the fusion of gametes and only has one parent. There is no mixing of genetic information, resulting in genetically identical offspring (clones). Mitosis is the only process involved in asexual reproduction. This type of reproduction is common in small animals, plants, fungi, and bacteria. Some larger plants such as daffodils and strawberries also reproduce asexually. On the other hand, sexual reproduction involves the fusion of male and female gametes, which are formed by meiosis. Meiosis leads to the formation of non-identical cells: sperm and eggs in animals, and pollen and egg cells in flowering plants. Sexual reproduction results in a mix of genetic information, leading to variation in the offspring. Though risky, sexual reproduction allows for variation which helps species to adapt and survive better.
Cell Division in Reproduction
Mitosis occurs constantly in tissues and during asexual reproduction. Meiosis, on the other hand, results in the formation of gametes, which have only half the original number of chromosomes. In animals, female gametes (ova) are made in the ovaries, while male gametes (sperm) are made in the testes.
Homologous Chromosomes
Meiosis involves the formation of gametes, which reduces the chromosome number. In body cells, there are two sets of each chromosome, one from each parent. During meiosis, genetic information is copied, resulting in four sets of each chromosome instead of the normal two sets. The cell then divides twice to form four genetically different gametes, leading to variation in offspring.
The Best of Both Worlds
Some organisms rely on both asexual and sexual reproduction, depending on the circumstances. For example, fungi commonly reproduce asexually, but they may reproduce sexually to give rise to variation if the weather conditions are not optimal.
Advantages of Sexual and Asexual Reproduction
Advantages of sexual reproduction include the production of variation in offspring, selective breeding, and adaptability to changing conditions. On the other hand, advantages of asexual reproduction include the use of less energy, time efficiency, and the ability to produce lots of identical offspring in favorable conditions.
DNA and the Genome
Genetic information is stored in the form of DNA which is made up of genes. These genes control proteins that in turn control the formation of specialized cells and tissues. The entire genetic material of an organism, including all the chromosomes and genetic material found in mitochondria, makes up its genome. Understanding the human genome is crucial for understanding inherited disorders and has great importance for medicine. The human genome consists of over 3 billion base pairs and almost 21,000 genes that code for proteins, and helps us understand inherited disorders such as cystic fibrosis.
DNA Structure
DNA, found in the nucleus of cells, is made up of small parts called nucleotides. The long strands of DNA alternate between sugar and phosphate molecules, with nitrogenous bases attached to the sugars. These nitrogenous bases form the genetic code.
