Inheritance

• Chromosomes


  Genetic material in the nucleus of a cell
• Human cells


  • Contain 23 pairs of chromosomes
• Mitosis


  Cell division process that produces two identical daughter cells
• Gametes


  Reproductive cells with single (unpaired) chromosomes
• Human gametes


  • Sperm cells and egg cells
• Meiosis


  Cell division process that produces genetically different gametes
• Meiosis takes place in flowering plants to produce pollen and egg cells
• Sexual reproduction


  Involves the fusion of male and female gametes, mixing genetic information
• Fertilization


  The fusion of a sperm cell and an egg cell
• Sexual reproduction results in variation in the offspring
• Asexual reproduction


  Involves only one parent, no mixing of genetic information, produces genetically identical offspring (clones)
• Asexual reproduction does not involve gametes or meiosis, only mitosis
• Asexual reproduction in plants


  • Forming tiny buds that drop off and grow into new plants
• Meiosis


  The process by which gametes (sperm and egg cells) are produced, with half the normal number of chromosomes
• Normal human cells


  • Contain 23 pairs of chromosomes
• Gametes (sperm and egg cells)

  • Contain 23 single chromosomes
• Meiosis


  1. Chromosomes are copied

  2. Cell divides into two

  3. Both cells divide one more time forming gametes
• Meiosis produces four gametes from one original cell, and each gamete is genetically different from the others
• Fertilization


  The joining of a male gamete (sperm) and a female gamete (egg) to form a new cell with the full number of chromosomes
• After fertilization, the new cell has 23 chromosome pairs
• After fertilization


  1. The new cell divides by mitosis, producing a clump of identical cells (an embryo)

  2. As the embryo develops, the cells differentiate, forming different cell types
• You'll find plenty of questions on meiosis and fertilization in the revision workbook
• Sexual reproduction


  • Offspring receive a mixture of genetic information from two parents
  • Produces variation in the offspring
  • Gives a species survival advantage by natural selection
• Asexual reproduction


  • Only one parent is needed
  • More efficient in both time and energy than sexual reproduction
  • Allows an organism to produce many genetically identical offspring rapidly
  • Risky because all the offspring are genetically identical
• Organisms that can reproduce by both sexual and asexual methods

  • Malaria parasite
  • Fungi
  • Flowering plants (e.g. strawberry)
  • Daffodils
• Asexual reproduction in malaria parasite

  1. Reproduces asexually in human host

  2. Reproduces sexually in mosquito vector
• Asexual reproduction in fungi

  Produce spores
• Asexual reproduction in strawberry plant

  Sends out runners, new plant develops where runner touches soil
• Asexual reproduction in daffodils

  Parent plant has underground bulb which produces buds, forming new offspring plants
• Flowering plants can reproduce sexually to produce seeds
• Strawberry is a good example of a plant that can reproduce asexually
• There will be plenty of questions on sexual and asexual reproduction in the revision workbook
• DNA


  Genetic material that determines inherited features
• DNA


  • Consists of two strands
  • Each strand is a polymer made by joining smaller molecules
  • The two strands wrap around each other to form a double helix
• Chromosome


  Contains the molecule DNA
• Gene


  A small section of DNA on a chromosome that encodes a specific sequence of amino acids to make a specific protein
• Humans have thousands of genes, with over 700 genes on chromosome 9
• Genome


  The entire genetic material of an organism
• Human genome


  • Has been studied by scientists
  • Helps search for genes linked to diseases like cancer and Alzheimer's
  • Helps understand and treat inherited disorders like cystic fibrosis
  • Helps trace human migration patterns from the past
• DNA


  Genetic material contained in chromosomes in the nucleus