Biology 1 ocr 21st century

Biology 1 ocr 21st century

1. Genes, Chromosomes and DNA

   • 1. Most cells have a nucleus containing your genetic material
   • 2. Genetic material in the nucleus is arranged into chromosomes of which there are 23 pairs
   • 3. Each chromosome is one long molecule of DNA that is coiled up
   • 4. A gene is a short length of a chromosome
   • 5. Genes control he development of different characteristics
   • 6. Genes exist in different versions called alleles
   • Genotype- the genes an organism has

2. Genes and Variation

   • Sperm and egg cells have half the normal amount of DNA
   • Children resemble both parents but are identical to neither
   • Genes are shuffled together randomly to make eggs and sperm
   • Half chromosomes are from each parent

3. Inheritance and Genetic Diagrams

   • Combination of alleles controls phenotype
   • Homozygous- two same alleles of a gene
   • Heterozygous- two different alleles of a gene
   • Alleles can be dominant or recessive

4. Sex Chromasomes

   • Control whether you are male or female
   • Men have XY
   • Women have XX
   • Determined by one gene
   • Control which hormones and sex organs are produced
   • Y causes protein to be formed- not formed in women

5. Genetic Disorders

   • Caused by faulty alleles
   • One or both parents carry a faulty allele
   • Huntingtons
     • Dominant allele
     • Tremors
     • Clumsiness
     • Memory loss
     • Mood changes
     • Poor concentration
     • Symptoms appear after 40
   • Cystic fibrosis
     • Thick sticky mucus
     • Breathing difficulty
     • Chest infections (painful coughing)
     • Difficulty digesting food
     • Recessive allele

6. Genetic Testing

   • Used on embryos children and adults
   • Embryos
     • Produced in IVF- check for genetic disorders (pre-implantation genetic testing)
     • Not 100% safe
       • Miscarriage
     • Cause people to terminate?
   • Children and adults
     • Checked if they carry alleles for genetic disorders so they can see if their child would inherit a disorder
     • Tested before drugs are prescribed to see how it will affect an individual
     • If one member of the family is tested should others?
   • False positive / false negative
   • If results become available there could be discrimination
     • Harder to get a job
     • More expensive insurance

7. Clones

   • Genetically identical organisms
   • Nature makes clones
     • Asexual reproduction
       • Bacteria- divide in two
       • Plants
         • Strawberry plants grow new runners
         • Garlic grow underground fleshy structures (bulbs)
     • Embryo cells split
       • Identical twins
         • Single egg fertilized by a single sperm
           • Embryo splits in 2
   • Clone in a lab
     • 1. Nucleus is removed from an egg cell leaving an egg
       • 2. nucleus from adult donor inserted in its place
         • 3. Cell stimulated and divides as normal

8. Stem Cells

   • Most cells in the body are specialised
   • Embryonic stem cells
     • Unspecialised and found in early embryos
     • Removed from the embryo then the embryo is destroyed
     • Potential to turn into ANY cell
   • Adult Stem Cells
     • Unspecialised
     • Involved in maintaining and repairing old and damages tissues
     • Can specialise into MANY (not all) cell types
     • Safely removed via bone marrow
   • Uses
     • Cure Sickle cell anaemia- bone marrow transplants
     • Replace faulty cells in the sick