science sem 1

• Genetic variation can lead to differences in traits among individuals, which can be advantageous, disadvantageous, or neutral depending on the environment.
• Genetics is the study of heredity: The passing of traits from parent to offspring
• Factors influencing what you are today

  • Heredity - the characteristics inherited from parents
  • Environment - all the factors that have acted on you throughout your life
• Trait


  A feature or quality (physical, behavioural, predisposition to a medical condition)
• Phenotype


  Description of the trait
• There are many genetic variations in people, as well as in other organisms
• Order of terms from largest to smallest

  • Organ
  • Cell
  • Tissue
  • Organelles
  • Organism
• The genome determines the traits of an individual
• Genes determine the traits of an individual
• DNA is a long molecule found in the nucleus of a cell, made of many nucleotides joined together
• Four types of DNA bases

  • Adenine (A)
  • Thymine (T)
  • Cytosine (C)
  • Guanine (G)
• A and T bond together & G and C bond together. A & T and C & G are called complimentary base pairs
• A triplet (3) of bases is called a codon and codes for an amino acid. Amino acids join to form proteins which make up most things in the body like hormones, muscle, and enzymes. Certain amino acid sequences are responsible for certain traits
• Genes are sections of DNA arranged along chromosomes. One gene is made up of many DNA bases in a particular order. Genes differ due to the different arrangement of DNA bases. The order of the bases is the genetic code for a hereditary characteristic (e.g., eye colour)
• DNA is packaged into thread-like structures called chromosomes. Human body cells have a set of 46 chromosomes arranged in 23 pairs called homologous pairs according to their size, shape, and bandings
• One of each homologous chromosomes comes from each parent. One pair of chromosomes comes from the mother and the other from the father. One pair are the sex chromosomes which determine whether you are male or female (XX = female, XY = Male). The other 22 pairs are called autosomes
• A human’s body cells will have 46 individual chromosomes (23 pairs) called the diploid number of chromosomes. A human’s sex cells will have 23 individual chromosomes (haploid number)
• One pair are the sex chromosomes which determine whether you are male or female
• XX


  Female
• XY


  Male
• The other 22 pairs are called autosomes
• A human’s body cells will have 46 individual chromosomes (23 pairs). This is called the diploid number of chromosomes
• A human’s sex cells will have 23 individual chromosomes (also called the haploid number)
• Mum’s sex cell (23) + Dad’s sex cell (23) = Your first body cell (46)
• Genetic disorders such as Down syndrome can be caused by differences in chromosomes
• Organisms and their number of chromosomes

  • Fruit Fly: 8, Frog: 26, Human: 46, Pea: 14
• You began your life as a zygote, a single egg cell that had been fertilised by a sperm cell
• Before cells divide, a copy of the DNA is made. The process of copying DNA is called replication
• DNA replication


  1. The strands of the double helix separate like a zip

  2. Nucleotides within the nucleus attach to both strands of the DNA

  3. Two identical double helix DNA molecules are produced
• Mitosis


  Produces two body cells that are identical to the parent cell. This type is involved in growth and repair of the body
• Meiosis


  Produces sex cells (eggs and sperm) that have half the number of chromosomes of the parent cell
• If you look more like one parent then you have inherited more of that parent’s genes
• The genetic information passed on to you from your parents came from their sex cells – that is from your father’s sperm and your mother’s egg cells
• Your genes determine ALL of your characteristics
• A mutation to any part of your DNA is always harmful
• Humans have 46 chromosomes, arranged in pairs. In each pair, one chromosome comes from the egg and one from the sperm. Each chromosome in a pair contains genes that code for the same genetic feature. These genes are called alleles. Alleles are different versions of the same gene
• Some genes can be dominant or recessive. Dominant genes: stronger and only need one to be present for the characteristic to show up. Recessive genes: weaker and need to have two of them for the characteristic to show up. Dominant genes are shown with a capital letter (B) and recessive genes are shown with a lower case letter (b)
• Genotype: Two letters that represent the
• Dominant genes


  Shown with a capital letter (B)
• Recessive genes


  Weaker and need to have two of them for the characteristic to show up