Heredity

• Heredity: Transmission of features/characters/traits from one generation to the next
• Genetics: Branch of science dealing with heredity and variation
• Variation: Differences among individuals of a species/population
• Mendel started experiments on plant breeding and hybridization with Pisum sativum (garden pea)
• Mendel observed contrasting characters in garden peas and their inheritance
• Chromosomes: Long thread-like structures in the nucleus containing hereditary information
• DNA: Chemical in chromosomes carrying traits in coded form
• Gene: Part of a chromosome controlling a specific biological function
• Contrasting characters: Pair of visible characters like tall and dwarf, white and violet flowers
• Dominant trait: Character expressing itself in the F1 generation
• Recessive trait: Character present but not expressed in a generation
• Homozygous: Condition with both genes of the same type present (e.g., TT for tallness)
• Heterozygous: Condition with genes of different types present (e.g., Tt for tallness and dwarfness)
• Genotype: Genetic makeup of an individual (e.g., TT for pure tall plant, Tt for hybrid tall)
• Phenotype: External appearance of an organism (e.g., plant with Tt genotype appearing tall)
• Homologous pair of characters: One from father and one from mother with genes for the same character
• Law of Dominance: Pure contrasting characters crossed result in only one character expressing itself in the F1 generation
• Mendel conducted monohybrid and dihybrid crosses with pea plants
• Monohybrid Cross: Shows inheritance of dominant and recessive characters
• In monohybrid cross, Mendel observed pure tall and pure dwarf pea plants resulting in F1 generation with only tall plants
• F2 generation from monohybrid cross had a phenotypic ratio of 3:1 for tall and dwarf plants
• Dihybrid Cross: Observes inheritance of two pairs of contrasting characters
• In dihybrid cross, Mendel obtained four different types of seeds in the F2 generation in a ratio of 9:3:3:1
• Cellular DNA is the information source for making proteins in the cell
• Gene provides information for a particular protein (e.g., growth hormone controlling plant height)
• Parents contribute equally to the DNA of the next generation during sexual reproduction
• Germ cells get a single set of genes from parents due to reductional division in sex organs during gamete formation
• Sex of a newborn individual is genetically determined in human beings
• Human sex determination: Females have XX chromosomes, males have XY chromosomes
• Autosomes: Chromosomes not involved in sex determination
• Sex chromosomes: Chromosomes determining the sex of the newborn
• Fertilization with X or Y chromosome sperm determines the sex of the baby (XX for female, XY for male)