CH6BIO

• Heredity is the transmission of features from parents to offspring
• Variations are features seen in offspring that are different from their parents
• Genetics is the branch of science that deals with heredity and variations
• Gregor Johann Mendel studied the inheritance of 7 pairs of contrasting traits in pea plants
• Mendel formulated the laws of inheritance by analyzing traits like height of plants, position of flower, shape of seed, color of seed coat, color of cotyledon, color of fruit, and shape of fruit
• Mendel explained that each character is controlled by a pair of factors, which he illustrated using symbols
• Genes are responsible for the transmission of characteristics from parents to offspring
• A gene that controls a character has different forms called alleles
• A gene generally has two alleles, one dominant and one recessive
• When plants with differing traits are hybridized, only one trait is expressed in the first generation (dominant trait) while the other remains hidden (recessive trait)
• During gamete formation, factors that determine a particular character segregate without getting mixed
• The ratio of dominant to recessive traits in the second generation is 3:1
• Variations in offspring are due to the independent assortment of each character
• DNA (Deoxyribonucleic Acid) is a molecule containing two strands with sugar, phosphate, and nitrogen bases
• DNA is made up of nucleotides containing sugar, phosphate, and nitrogen bases
• DNA has four nitrogen bases: adenine, thymine, guanine, and cytosine
• RNA is another nucleic acid formed of nucleotides with ribose sugar and uracil base
• Genes contain information for protein synthesis and are segments of DNA
• Protein synthesis is controlled by the activity of specific proteins (enzymes)
• Human beings have 46 chromosomes, with 44 somatic chromosomes and 2 sex chromosomes
• Females have two X chromosomes (44 + XX) and males have one X and one Y chromosome (44 + XY)
• Crossing over of chromosomes during meiosis leads to the exchange of genetic material and new gene combinations
• Fertilization causes variations in offspring due to the combination of alleles from gametes
• Mutations are sudden heritable changes in the genetic constitution of an organism, leading to variations in characters
• Melanin, a pigment protein, determines the color of human skin through the function of alleles of genes responsible for skin color
• He

  studied the inheritance of 7 pairs

  of contrasting traits in pea plants,

  scientifically known as Pisum

  sativum.
• DNA does not participate directly in protein synthesis. DNA performs

  its activities with the help of RNA. RNA that carries information

  from DNA reaches ribosome and controls protein synthesis. Since

  this RNA is the messenger of DNA, it is called messenger RNA or

  mRNA. Besides mRNA, there are tRNA (Transfer RNA) that carry

  amino acids to the ribosomes and rRNA (Ribosomal RNA) that are

  seen associated with ribosomes. Protein molecule is synthesized by

  the combined activities of all these molecules.