Genetics and Health

• Genes control the characteristics of individual cells (height,eye colour, hair colour)
• only a fraction of the total number of genes in each cell is expressed
• in the production of gametes only one chromosome from each pair is carried into the sex cell
• chromosomes occur in homologous pairs (2 copies of every gene) but it is possible that the 2 copies are different
• the genotype is the alleles that are carried for a particular gene and show the allele arrangement in an individual (TT/Tt/tt)
• the phenotype is visible characteristic that is produced by the genotype (tall/small)
• homozygous is when both alleles of a gene are the same (TT)
• Heterozygous is when the alleles of a gene are different (Tt)
• genetic conditions are caused by a fault with genes/chromosomes
• haemophilia is a problem with blood clotting mechanism and gives a high risk of excessive bleeding
• haemophilia is a sex linked inherited condition which is a recessive allele in the X chromosome (most common in males)
• cystic fibrosis is a recessive allele which causes frequent and serious lung infections and problems with food digestion
• huntingtons disease affects nerve cells in the brain and is more apparent in middle age
• huntingtons disease is a dominant allele and is fatal with no cure
• down’s syndrome occurs by chance when there is a random change to the number of chromosomes.
• a person with down syndromes chromosomes in position 21 fail to seperate and gametes are made with two of chromosome 21 instead of one meaning the child has 47 chromosomes
• Male XY Female XX
• X is larger than Y so it can carry genes not present on Y
• Females are mostly carriers of sex linked diseases
• Recessive alleles on males X chromosome will show as there is no dominant allele
• genetic screening is used to reduce the incidence of conditions caused by problems with our chromosomes
• genetic screening tests people for the presence of a particulate allele or condition
• in amniocentesis tests foetal cells are taken from amniotic fluid and allowed to multiply in lab conditions. they are then examined to see if the foetus has a condition.
• amniocentesis tests carrie 1% risk of miscarriage and is only used with pregnant woman with risks such as

  1. older mothers
  2. previously carried a foetus with genetic abnormality
  3. family history
  4. possible problems identified in earlier blood tests
• in meiosis the female gives 1 X chromosome from each egg and the male gives 1/2 an X chromosome and 1/2 a Y chromosome
• mendels law of segregation states that the 2 alleles of each pair of genes seperate during meisois with only 1 of each pair being present in a gamete
• In genetic engineering DNA is extracted from the donor and added to genetic material (organism) in the recipient
• in genetic engineering DNA is incorporated into DNA of bacteria as it is easily manipulated and reproduces rapidly in special fermenters/bioreactors therefore producing a valuable product (drug/hormone)
• when making insulin the gene coding is removed from human DNA using a restriction enzyme
• the restriction enzyme used to orginally remove human DNA for insulin is also used to remove and cut plasmid DNA from a bacterium
• The insulin and bacterial plasmid DNA that has been taken is joined by another enzyme
• to make the insulin’s the modified plasma is added back to the bacterial cell which multiplies in fermenters, It is then extracted purified and packaged (downstreaming)
• restriction enzymes are used to cut and isolate the human insulin gene and bacterial plasmid DNA
• insulin was fomerly extracted from pancreases of domestic animals but it was a slow process which produced a limited amount and not as effective
• genetically engineered insulin is produced in large amounts, is compatible and cheap