genetics - biology

• Sexual Reproduction


  Genetic information from two organisms (a father and a mother) is combined to produce offspring which are genetically different to either parent
• Sexual Reproduction


  1. Father and mother produce gametes (reproductive cells)

  2. Gametes only contain half the number of chromosomes of normal cells (haploid)

  3. Fertilisation - male gamete fuses with female gamete to produce a zygote (with full set of chromosomes, diploid)

  4. Zygote undergoes cell division (mitosis) and develops into an embryo

  5. Embryo inherits characteristics from both parents
• Meiosis


  A type of cell division that produces genetically different cells, happens in reproductive organs
• Meiosis


  1. DNA duplicates before cell division

  2. Chromosomes line up in pairs in the centre of the cell

  3. Pairs are pulled apart, each new cell gets one copy of each chromosome (from mother and father)

  4. Second division separates chromatids, producing 4 haploid daughter cells (gametes)
• Human cells contain 46 chromosomes, so diploid number is 46 and haploid number is 23
• Gametes

  Sperm and egg cells
• In flowering plants, male gametes are in pollen and female gametes are in ovaries
• Each chromosome arm in a duplicated chromosome is identical
• Half the chromosomes in a cell come from the organism's father, half from its mother
• DNA

  Molecule that carries instructions for characteristics, made up of nucleotides
• DNA structure


  1. Strands made of sugar-phosphate backbone with bases (A, T, C, G)

  2. Bases pair up (A-T, C-G) in a double helix
• Chromosomes

  Long, coiled up molecules of DNA found in cell nucleus
• Gene

  Section of DNA on a chromosome that codes for a particular protein
• Genome


  All of an organism's DNA
• Extracting DNA from fruit cells

  1. Mash fruit, add detergent (breaks down cell membranes to release the DNA) and salt (make the DNA stick together)

  2. Filter mixture

  3. Add ice-cold alcohol to filtered mixture

  4. DNA will appear as stringy white precipitate - can be fished out with glass rod
• Alleles

  Different versions of the same gene
• Homozygous


  Having two of the same alleles for a gene
• Heterozygous


  Having two different alleles for a gene
• Dominant allele


  Allele that overrules a recessive allele