B1 | Mind Map

Genes, Chromosomes and DNA
1. Most cells in body have a nucleus - contains genetic material
2. Genetic material arranged into chromosmes
  1. Human body has 23 pairs of chromosomes
  2. Chromosomes is a long molecule of DNA coiled up
3. A gene is a short length of chromosome
  1. Genes control the development of different characteristics
  2. Genes have different variations, which form different characteristics
  3. Genes encode certain proteins
    1. Structural proteins make up things like skin, hair, blood
    2. Functional proteins make up enzymes etc.
  4. Genotype describes all the genes it has
  5. Phenotype is the characteristic of the gene
4. Genetic factors affect things like dimples, eye colour or natural hair colour
5. Environmental factors are physical changes like scars or the dyeing of hair
Genes and Variation
1. Chromosomes come in pairs (because we have 2 parents)
  1. Each sex cell contains 23 individual chromosomes
  2. Upon fertilisation, the 23 chromosomes from each sex cell combine to make 23 pairs.
  3. The two chromosomes in the pair contain the exact same genes in the exact same places, they may contain varying alleles
2. Half a child's chromosomes come from each parent
  1. Children get some alleles from each parent
  2. Children look similar to both but identical to neither of their parents
3. Homozygous: two alleles the same for the particular gene
4. Heterozygous: two alleles different for the particular gene
5. Dominant allele: only the characteristic of the dominant allele is shown, as long as it is present no matter what the genotype is
6. Recessive allele: the characteristic is only shown if the genotype is homozygous recessive
Sex Chromosomes
1. 23rd chromosome pair labelled XY
  1. Men have XY
    1. Y causes male characteristics
  2. Women have XX
    1. Lack of Y causes female characteristics
Genetic Disorders
1. Cystic Fibrosis
  1. Symptoms
    1. Thick sticky mucus in air passages
    2. Breathing difficulty
    3. Chest infections
    4. Difficulty digesting food
  2. Caused by recessive allele
  3. Carried by 1 in 25 people
  4. For a child to have CF, parents must be carriers or sufferers
  5. 1 in 4 chance if both parents are carriers
2. Huntington's
  1. Symptoms
    1. Tremors
    2. Clumsiness
    3. Memory Loss
    4. Mood changes
    5. Poor Concentration
  2. Caused by a dominant allele
  3. Late onset
  4. 50% chance of child inheriting if parent is a carrier
3. Genetic Testing
  1. Embryos produced via IVF are tested using pre-implantation gnetic diagnosis. Only used if parent has history of genetic disorders.
    1. Healthy embryos implanted
    2. Faulty embryos discarded
  2. Tests aren't 100% accurate
    1. Misinterpreted
    2. Contaminated
  3. Not 100% safe. e.g. risk of miscarriage when testing fetuses
  4. Insurance refused for wrong alleles
Clones
1. Clones are genetically identical organisms
  1. Differences arise due to to environmental factors
2. Natural Clones
  1. Asexual reproduction results in identical offspring to the parent and all siblings
  2. Bacteria (dividing into two)
  3. Some plants reproduce asexually also. Strawberry plants send out runners to plant new clones at their tips
  4. Some animals reproduce asexually. Female greenfly don't need to mate, they can just lay eggs.
  5. Identical twins are also clones
  6. A single egg fertilised by sperm splits into two.
  7. The two embryos are genetically identical, two genetically identical babies are born.
3. Scientific Clones
  1. Nucleus of an egg is removed
  2. Nucleus from a donor cell is removed (non -sex-cell)
  3. Cell is stimulated so it starts dividing
  4. Embryo produced is genetically identical to donor cell
Stem Cells
1. Can become other types of cell
2. Most normal cells are already specialised
3. Stem cells can specialise into other types of cells, depending on the instructions given
4. Embryonic Stem cells
  1. Unspecialised cells found in early embryos
  2. Removed, embryo is then destroyed
  3. They can specialise into ANY type of cell
5. Adult Stem Cells
  1. Unspecialised cells found in adult animals
  2. Involved in maintaining and repairing old and damaged tissues
  3. Safely removed e.g. from bone marrow - no embryos have to be destroyed
6. Can be used to replace blood cells to cure sickle cell anaemia
7. Embryonic stem cells could be used to replace faulty cells in sick people. e.g. new organs

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	Created by benevans2000 about 8 years ago