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Genetic Diseases. Objectives. To recap genetic inheritance To identify four genetic diseases To review key factors to study To propose research. Reproduction:. The gametes (sex cells of humans each contain 23 chromosomes . This is half the number of all other cells .
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Objectives • To recapgeneticinheritance • To identifyfourgeneticdiseases • To reviewkeyfactors to study • To proposeresearch
Reproduction: • Thegametes (sex cells of humanseachcontain 23 chromosomes. Thisishalfthenumber of allothercells. • When the sperm meets the egg their nuclei fuse giving 23 pairs (46) chromosomes. The number present in all of our cell nuclei (except our sperm and eggs)
Features • Many of our features are controlled by the genes on our chromosomes. • This is why we often look like our parents. • But we don’t always. • We will discuss the reasons.
Important terms • Alleles:These are alternativetypes of one gene. • Homozygous:Youhavethesametwoallelesfor a gene. • Heterozygous:Yourtwoalleles are different • Genotype:Thecombination of allelesthatyouhave. • Phenotype:Thefeaturesyouactuallyhave. This is a human karyotype – all the chromosomes laid out. You can see they are in pairs
Other important terms • Dominant: You only need one of your two alleles to be this to see it. It means the phenotype is the same whether you are homozygous (have two dominant alleles) or heterozygous (have one dominant allele) Example Huntington’s disease: you have it if you inherit the allele from one parent • Recessive: you need both of your alleles to be this to see its affects. Your phenotype only shows this if you are homozygous: have two recessive alleles. E.g. Cystic fibrosis and others…….
Albinism • Albinos don’tnormallyhave albino parents. Itis a recessivecondition and an albino musthavetwo albino alleles. • Thatmeanstheymusthavegotone albino allelefromeachparent. • One in every 130 individualscarriesthe gene foralbinismbuttheconditionismuchlesscommonbecausebothparentsmustbecarriers and thechildmustinheritthe albino allelefromboth (a 1 in 4 chance). • Onechild in every 17000 is albino.
Example Cystic Fibrosis • Also known as mucoviscidosis (sticky mucus) • Developmental disease • Lungs do not develop properly • Digestive system does not absorb food • Pancreas stops functioning • Observed in infancy • Untreated leads to very early death • Treated increases survival but likely to reduce growth • Some people seem very healthy • Others seriously compromised
Complications • Many respiratory infections • Poor growth due to malnutrition • Diabetes due to damage to pancreas • Intestinal blockage in newborns • Sterility due to blockage of sperm duct (sperms fine) • Cirrhosis of the liver
Inheritance • This is a recessive disease • This means you must have both alleles to have the disease; • If you have one allele you are a carrier and do not show the disease; • Both parents must be carriers for a child to have a disease • Chance of having disease is 1 in 4
Pathology • CF is caused by a mutation in the gene for the protein cystic fibrosis transmembrane conductance regulator (CFTR); • This protein regulates the components of digestive juices, sweat and mucus; • Only one healthy gene is needed for this to function
Genetics • There are over 1500 possible mutations to the CFTR gene that can lead to CF • Over 60% of cases worldwide are due to one specific mutation; • Screening usually tests for up to 32 different mutations, but this does mean that some cases can be missed by screening.
Prevalence • Commonest in western European Caucasians (1 in 25 are carriers) • Highest prevalence in Ireland • Non European populations much rarer and usually a different mutation (1 in 46 Hispanics in US, 1 in 65 African Americans) • In 1959 median age of survival was 6 months • The median survival age in Canada has increased from 24 in 1982 to 47.7 in 2007
Treatment and cure • Possible cure through introduction of gene to airways – early stages • Treatment of lung diseases through antibiotics • Preventative use of antibiotics • Physiotherapy to help clear lungs of fluid • Replacement of digestive enzymes (pills) • Insulin • Healthy diet and exercise • May need lung, liver and pancreas transplants • Assisted reproduction
Prevention • At risk adults may get genetic testing. • Expensive so usually only one parent done at first (many mutations screened for) • Pre-implantation genetic diagnosis • Testing of foetus in uteroby amniocentesis or chorionic villus sampling of placenta • Screening of new born: test sweat • Parents may notice baby tastes salty • Worst option wait till respiratory complications and poor growth show; • Best prognosis with earliest diagnosis
Amnioscentesis Carries a risk of about 1 in 200 of initiating an abortion
Ethics • What ethical issues surround the following decisions • 1. To start a family • 2. To test foetuses • 3. To decide against having a child • 4. Gene testing and medical records
Rubric • 1 mark = a relevantpiece of info • 2 marks = severalrelevantpieces of info • 3 marks = mostrelevantinfothere • 4 marks = Comprehensiveinformationclearlyexpalined. • Ten contentareas: 4 marks per area, total out of 40.
