genetics

• Cell cycle is the sequence of events occurring between the cell formation and its division
• Consists of two phases: Interphase and Mitotic phase (M-phase)
• Interphase is the interval between two successive cell divisions, divided into 1 G phase, S-phase, 2 G phase
• Cell division involves replication of DNA, division of nucleus or karyokinesis, and division of cytoplasm or cytokinesis
• There are two types of cell division: Mitosis and Meiosis
• Mitosis is for growth, development, repair, and replacement
• Meiosis is for production of gametes
• Mitosis occurs in four phases: prophase, metaphase, anaphase, and telophase
• Prophase: chromosomes become short and thick, move towards the equator, each chromosome duplicates to form two chromatids attached at centromere
• Metaphase: chromosomes arrange on the equatorial plane, attached to spindle fibre at centromere
• Anaphase: centromere divides, sister chromatids separate and move towards opposite poles
• Telophase: chromatids become thinner, nuclear membrane and nucleolus reappear
• Mitosis is followed by division of cytoplasm (cytokinesis)
• Meiosis produces sex cells or gametes, halves the number of chromosomes
• Meiosis has two divisions: meiosis I (reduction division) and meiosis II (equational division)
• Chromosomes are made of DNA and proteins
• DNA molecule is a double chain of nucleotides in a helix, with a sugar molecule, phosphate group, and organic base in each nucleotide
• Genes are specific parts of chromosomes composed of DNA, responsible for hereditary characters and transmission of traits
• Four types of chromosomes: metacentric, submetacentric, acrocentric, telocentric
• Metacentric: centromere in the centre, two equal arms of chromatid
• Telocentric: centromere at one end of chromosome
• Submetacentric: centromere slightly away from centre, one arm slightly larger
• Acrocentric: centromere near one end, one arm very large compared to the other
• Genetics is the branch of science that studies inheritance and variations
• Heredity is the transmission of characters from one generation to the next
• Gregor Johan Mendel is known as the Father of Genetics and conducted extensive experiments on garden peas
• Mendel's Laws of Inheritance:

  • Law of dominance: one character dominates over the other in offspring
  • Law of segregation: factors segregate during gamete formation and restore paired conditions in the next generation
  • Law of independent assortment: inheritance of each contrasting character is independent of others
• Dominant character is fully expressed in offspring, while recessive character remains masked and expresses only in homozygous condition
• Allele is a gene controlling a character, with alternative forms affecting characteristics differently
• Homozygous has identical alleles, while heterozygous has different alleles (one dominant, one recessive)
• Phenotype is the observable genetically controlled character, while genotype is the combination of genes in an organism
• Chromosomes are thread-like structures carrying genetic information, genes are the basic unit of heredity found on chromosomes
• Genome is the full complement of DNA including all genes and intergenic regions of an organism
• Monohybrid cross involves alternative traits of one character, while dihybrid cross considers alternative traits of two different characters
• Each chromosome consists of two chromatids joint at a centromere point, containing genes that control characters and transmit hereditary information
• The number of chromosomes is fixed in a species, with 23 pairs (46) in humans, maintained through meiotic division
• Non-disjunction in meiosis can lead to abnormal chromosome numbers, causing genetic abnormalities like Down's syndrome
• Linkage is the tendency of genes to stay together in hereditary transmission, known as linked genes
• Mutation is a sudden change in genes in progeny that may not have existed in previous generations, leading to variations in individuals of the same species