B1

B1

1. B1

   • Genetic traits
     • Passed through genes
       • Either dominant or recessive
   • Sex deterimination
     • If a defective gene in found on parts of the X chromosome, it can result in sex-linked diseases
       • More likely in men
     • Female has two X chromosomes
       • Male has an X and a Y chromosome
         • The Y chromosome triggers the growth of the testes, without it, ovaries develop
   • Gene disorders
     • Some disorders are caused by faulty or defective alleles
     • Huntington's disease is a dominant disorder
       • Occurs in middle age
       • Symptoms include tremors, memory loss, inability to concentrate and mood changes
     • Cystic fibrosis is a recessive disorder which means both alleles must be recessive for you to get it
       • Symptoms includes production of thick gluey mucus that affects lungs and digestion, breathing problems and chest infections
       • You can be a carrier for this and still be normal

2. We're all different

   • Characteristics controlled by genes and enviroment
   • Phenotype= physical
   • Genotype= genetic

3. What genes do

   • Functional proteins enable body to function
   • Structural proteins give the body structure
     • DNA= packed into chromosomes
       • Carry instructions= control how develop& function
         • Tells body what proteins it needs
           • Gene=section of DNA

4. Genes& chromosomes

   • Sex cells= 23 chromosomes
     • 46 cmromosomes
     • At fertilisation= Zygote
       • Combination from parents causes variation
         • Pairs of chromosomes have genes for the same characteristic

5. Alleles

   • Different forms of gene
     • Homozygous= same
     • Heterozygous= different

6. Genetic testing

   • Genetic screening is used to check for a disorder even when there is no history
     • Genetic testingis carried out when a genetic disease runs in the family
       • Ethical issues include who should know if someone has a disorder like Huntington's
         • Tests during pregnancy carry risk of miscarriage
           • IVF allows doctors to only implant normal embryos
             • Ethical issues include playing God however can allow people to plan

7. Stem cells

   • A human embryo develops from a single cell
     • Five days= ball of cells containing embryonic stem cells
       • These are unspecialised and can turn into any cell in body
         • Adult stem cells have limited uses
         • Ethical issues
           • Usually taken from unused embryos in fertility treatments
             • Using them involves destroying embryos

8. Cloning

   • Have identical genes
     • In asexual reproduction the offspring is in identical to the parent
       • Identical twins happen when a fertilised egg splits
         • Artificial cloning: Nucleus from body cell is inserted into egg cell then implanted into surrogate mother