Inheritance, Variation and Evolution

    Cards (108)

    • Meiosis
      The formation of four non-identical cells from one cell
    • Mitosis
      The formation of two identical cells from one cell
    • Sexual reproduction
      1. Joining of male and female gametes, each containing genetic information from the mother or father
      2. Sperm and egg cells in animals
      3. Pollen and egg cells in flowering plants
    • Gametes are formed by meiosis, as they are non identical
    • A normal cell has 46 chromosomes. There are two sets of chromosomes (i.e. 23 pairs). In each pair, one chromosome is from the father and the second set is from the mother
    • Each gamete has 23 chromosomes and they fuse in fertilisation
    • The genetic information from each parent is mixed, producing variation in the offspring
    • Asexual reproduction
      One parent with no gametes joining, using the process of mitosis to form two identical cells from one cell
    • There is no mixing of genetic information in asexual reproduction
    • Asexual reproduction leads to clones, which are genetically identical to each other and the parent
    • Organisms that reproduce asexually
      • Bacteria
      • Some plants
      • Some animals
    • Meiosis
      1. Cell makes copies of its chromosomes
      2. Cell divides into two cells, each with half the amount of chromosomes
      3. Cell divides again producing four cells, each with a quarter the amount of chromosomes
      4. These cells are called gametes and they are all genetically different from each other
    • Gametes with 23 chromosomes join at fertilisation to produce a cell with 46 chromosomes, the normal number
    • This cell divides by mitosis to produce many copies, and an embryo forms
    • The cells begin to take on different roles after this stage (differentiation)
    • Advantages of sexual reproduction
      • Produces variation in offspring
      • Allows selective breeding
    • Advantages of asexual reproduction
      • Only one parent is needed
      • Uses less energy and is faster as organisms do not need to find a mate
      • In favorable conditions lots of identical offspring can be produced
    • Organisms that use both sexual and asexual reproduction
      • Malarial parasites
      • Some fungi
      • Some plants
    • DNA
      The genetic material in the nucleus of a cell, composed of a chemical called DNA
    • Gene
      A small section of DNA on a chromosome - a triplet of bases that codes for a specific protein
    • Genome
      All the genes coding for all of the proteins within an organism
    • The whole human genome has now been studied and this has improved our understanding of the genes linked to different types of disease, the treatment of inherited disorders and has helped in tracing human migration patterns from the past
    • DNA structure
      • DNA is a polymer made up of two strands which wrap around each other like a rope - in a structure called a double helix
      • Between the two strands are the four nitrogenous bases lined up in single rows - these come together to form a series of complementary pairs
    • Protein synthesis
      1. DNA contains the genetic code for making a protein, but it cannot move out of the nucleus
      2. The two strands pull apart and mRNA nucleotides match to their complementary base on the strand
      3. The mRNA nucleotides are joined together, creating a new mRNA strand
      4. The mRNA moves out of the nucleus to the cytoplasm and onto ribosomes
      5. At the ribosomes, the bases on the mRNA are read in threes to code for an amino acid
      6. The corresponding amino acids are brought to the ribosomes by carrier molecules
      7. These amino acids connect together to form a protein
      8. When the chain is complete the protein folds to form a unique 3D structure
    • Protein functions
      • Enzymes - biological catalysts that speed up the rate of reaction
      • Hormones - chemical messengers that send signals around the body
      • Structural protein - strong proteins in order to form structures, such as collagen
    • Mutations
      Changes the sequences of bases in DNA, either by insertion, deletion or substitution
    • Most mutations do not alter the protein or only do so slightly
    • Some mutations can have a serious effect and can change the shape of the protein</b>
    • There can also be mutations in the non-coding parts of DNA that control whether the genes are expressed
    • Gamete
      An organism's reproductive cell (egg in female and sperm in males), which has half the number of chromosomes (23)
    • Chromosome
      A structure found in the nucleus which is made up of a long strand of DNA
    • Gene
      A short section of DNA that codes for a protein, and therefore contribute to a characteristic
    • Alleles
      The different forms of the gene - humans have two alleles for each gene as they inherit one from each parent
    • Dominant allele

      Only one (out of the two alleles) is needed for it to be expressed and for the corresponding phenotype to be observed
    • Recessive allele
      Two copies are needed for it to be expressed and for the corresponding the phenotype to be observed
    • Homozygous
      When both inherited alleles are the same (i.e. two dominant alleles or two recessive alleles)
    • Heterozygous
      When one of the inherited alleles is dominant and the other is recessive
    • Genotype
      The combination of alleles an individual has, e.g. Aa
    • Phenotype
      The physical characteristics that are observed in the individual, e.g. eye colour
    • Family trees show the inheritance of different phenotypes over generations in the same family