You and Your Genes Revision Lesson 2

What causes inherited diseases? Write: Huntington’s disorder and cystic fibrosis are inherited diseases. Huntington’s disorder and cystic fibrosis are inherited diseases. They are caused by ‘faulty’ alleles of just one gene. They are caused by ‘faulty’ alleles of just one gene.

Huntington’s Disorder Does not usually develop until over 35 years. Does not usually develop until over 35 years. Is fatal Is fatal Symptoms: Loss of memory and mental deterioration, loss of control over movements. Symptoms: Loss of memory and mental deterioration, loss of control over movements. One faulty dominant allele (H) causes it, so it can be inherited from just one parent. One faulty dominant allele (H) causes it, so it can be inherited from just one parent.

hh HHhHh hhhhh Father with hh alleles (does not have disorder) Mother with Hh alleles (does have disorder) How is Huntington’s inherited? There is a 50% chance that a child of these parents will inherit the disorder.

Cystic Fibrosis People with cystic fibrosis produce thick, sticky mucus. People with cystic fibrosis produce thick, sticky mucus. This mucus: This mucus: –Blocks the lungs and air passages –Prevents enzymes getting to gut –Encourages bacterial growth and infection A faulty recessive allele causes the disease so you need 2 copies of the allele to have it. A faulty recessive allele causes the disease so you need 2 copies of the allele to have it. A person with one faulty allele is a carrier A person with one faulty allele is a carrier –They don’t have symptoms, but can pass it on

How is Cystic Fibrosis inherited? Ff FFFFf fFfff Father with Ff alleles (carrier of CF) Mother with Ff alleles (carrier of CF) There is a 25% chance that a child of these parents will inherit cystic fibrosis. There is a 50% chance that a child will be a carrier of cystic fibrosis.

Genetic Testing How is genetic testing used? To know if a person is a carrier of a genetic disease doctors extract genes from white blood cells and test them for ‘faulty’ alleles. To know if a person is a carrier of a genetic disease doctors extract genes from white blood cells and test them for ‘faulty’ alleles. Cells can also be taken from young fetuses and tested. If the test is positive, parents may terminate the pregnancy. Cells can also be taken from young fetuses and tested. If the test is positive, parents may terminate the pregnancy.

Health authorities could test a whole population for a disease-causing allele. This is genetic screening (expensive but maybe cheaper than treating illness). Health authorities could test a whole population for a disease-causing allele. This is genetic screening (expensive but maybe cheaper than treating illness). Insurance companies could use genetic testing to assess risk (not allowed in UK). Insurance companies could use genetic testing to assess risk (not allowed in UK).

How can parents avoid having a baby with a genetic disease? If one or both parents are carriers: If one or both parents are carriers: –In vitro fertilisation (fertilising eggs with father’s sperm in a lab. –Pre-implantation diagnosis (doctors test one cell from eight-cell embryo for ‘faulty’ alleles. –Embryo selection (doctors choose embryo without faulty gene and implant in mother’s uterus. These techniques are not always successful

Gene therapy Scientists think some genetic diseases can be cured by gene therapy Scientists think some genetic diseases can be cured by gene therapy Faulty alleles are replaced with normal alleles from healthy person. Faulty alleles are replaced with normal alleles from healthy person. Has worked, but not for cystic fibrosis. Has worked, but not for cystic fibrosis.

Stem Cells Embryos contain stem cells Embryos contain stem cells These are unspecialised cells that can develop into any kind of cell. These are unspecialised cells that can develop into any kind of cell. Doctors hope to use them in the future to cure diseases. Doctors hope to use them in the future to cure diseases.

Clones Some bacteria, plants and simple animals reproduce asexually to make clones. Some bacteria, plants and simple animals reproduce asexually to make clones. Offspring have identical genes to the parent. Offspring have identical genes to the parent. Differences are causd by environmental factors. Differences are causd by environmental factors.

Animals do not usually form clones but: Animals do not usually form clones but: –Identical twins are clones of each other –Scientists have made clones They: – removed an egg cell nucleus –Took another nucleus from an adult body cell and transferred it into the ‘empty’ egg cell. –Grew the embryo for a few days, then implanted it into a uterus. –Offspring born as an identical clone of ‘adult cell’ animal.