Meiosis and Gamete Formation

Meiosis

• Meiosis is a type of cell division that occurs in reproductive organs to form gametes.
• Meiosis halves the number of chromosomes in gametes, resulting in genetically different gametes.
• The process of meiosis involves copying genetic information, dividing twice, and forming four gametes with a single set of chromosomes.

Types of Reproduction

• There are two types of reproduction: sexual and asexual.
• Sexual reproduction involves the fusion of male and female gametes, resulting in genetic variation in offspring.
• Asexual reproduction involves only one parent and no fusion of gametes, resulting in genetically identical offspring (clones).

DNA, Genes, and Chromosomes

• DNA is a polymer made up of two strands that form a double helix.
• DNA is contained in structures called chromosomes.
• A gene is a small section of DNA on a chromosome that codes for a particular sequence of amino acids to make a specific protein.
• The genome of an organism is the entire genetic material of that organism.
• Every chromosome has a pair, resulting in two copies of each gene in every genome.

Inheritance

• Some characteristics are controlled by one gene, and different versions of genes are called alleles.
• The genotype (set of alleles) determines the phenotype (physical characteristic).
• A dominant allele is always expressed when present, while a recessive allele is only expressed when there are two copies of it.
• Punnett square diagrams can be used to predict the genotypes of offspring.

Inherited Disorders

• Polydactyly is an inherited disorder caused by a dominant allele, resulting in extra digits.
• Cystic fibrosis is an inherited disorder caused by a recessive allele, resulting in lung problems due to a faulty cell membrane protein.
• An individual can be a carrier of a recessive disorder but not of a dominant disorder.

Sex Determination

• Ordinary human body cells contain 23 pairs of chromosomes, with one pair carrying the genes that determine sex.
• In females, the sex chromosomes are XX, while in males, the sex chromosomes are XY.

Advantages of Reproduction

• Sexual reproduction produces variation in offspring, which can lead to a survival advantage through natural selection.
• Asexual reproduction requires only one parent, is more time and energy efficient, and allows for faster reproduction and many identical offspring.

Development of Genetics

• Gregor Mendel's breeding experiments on plants in the mid-19th century laid the foundation for modern genetics.
• The discovery of chromosomes and their behavior during cell division led to the idea that genes are located on chromosomes.
• The discovery of DNA's structure and function in the mid-20th century led to the development of the gene theory.

DNA and Protein Synthesis

• DNA is made up of nucleotides, which are composed of sugar, phosphate, and one of four bases.
• The sequence of three bases codes for a particular amino acid, which is assembled into a protein chain.
• Proteins are synthesized on ribosomes according to a template, and their unique shape enables them to perform specific functions.
• Mutations can occur in DNA, resulting in changes to the protein synthesised by a gene.

Learn about the process of meiosis, how it reduces the number of chromosomes in gametes, and the formation of a zygote through fertilization.