Inheritance, Variation and Evolution

• meiosis:


  sexual -> 4 non-identical cells from 1 cell.

  joining of male + female gametes (sperm, egg -> 23 chromosomes each).

  genetic information is mixed, producing variation in offspring.
• mitosis:


  asexual -> 2 identical daughter cells from 1 cell

  • no mixing of genetic information
  • clones
  • plants, bacteria and some animals
• advantages and disadvantages of sexual reproduction:


  .

  
• chromosome:


  a structure found in the nucleus, which is made up of a long strand of DNA
• gene:

  • section of DNA that codes for a protein
  • some characteristics are controlled by a single gene, most characteristics are results of genes interacting
• alleles:


  different forms of the gene- humans 2 alleles for each gene, inherit 1 from each parent
• homozygous:


  when both inherited alleles are the same
• heterozygous:

  when one of the inherited alleles is dominant and the other is recessive
• phenotype


  physical characteristics
• polydactyly:

  having extra fingers or toes
• embryonic screening: screening of embryos to identify those with genetic disorders.

  
• females (XX chromosomes), males(XY chromosomes)
• phenotypes depend on the genotype and environment.
• evolution:


  a change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species.
• selective breeding:

  is when humans choose which organisms to breed to produce offspring with a certain desirable characteristic.

  > Parents with desired characteristics are chosen.

  >bred together until desired characteristic
• disadvantages of selective breeding:

  • reduction of gene pool
  • inbreeding
  • changes of environment of new disease the species could become extinct
• genetic engineering:

  • modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic.
• archaea:


  primitive bacteria which live in extreme environments such as hot springs
• 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
• Normal cell


  Has 46 chromosomes, two sets of 23 chromosomes (one from each parent)
• Gamete


  Has 23 chromosomes, fuses in fertilisation
• The genetic information from each parent is mixed, producing variation in the offspring
• Asexual reproduction


  1. One parent with no gametes joining

  2. Happens using the process of mitosis, where two identical cells are formed from one cell

  3. No mixing of genetic information

  4. 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, has double the amount of genetic information

  2. Cell divides into two cells, each with half the amount of chromosomes (46)

  3. Cell divides again producing four cells, each with a quarter the amount of chromosomes (23)

  4. These cells are called gametes and they are all genetically different from each other because the chromosomes are shuffled during the process, resulting in random chromosomes ending up in each of the four cells
• 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 for 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 chromosomes of the nucleus of a cell

  • a polymer made up of 2 strands (wrap around each other like a rope) - in a double helix structure
• Gene


  A small section of DNA on a chromosome - a triplet of bases that codes for a specific protein

  each gene codes for a particular sequence of amino acids, together a chain of amino acids can join to make a 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
• 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