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Patterns of Genetic Inheritance

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  2. Patterns of Genetic Inheritance Rels 300 / Nurs 330 13 February 2014

  3. GENES ON CHROMOSOMES • 23 pairs of chromosomes • 1 out of each pair comes from maternal ovum • 1 out of each pair comes from paternal sperm • 22 are matched pairs • x and y are sex chromosomes • males have 1 x and 1 y • females have 2 x’s 300/330 - appleby

  4. X-LINKED INHERITANCE Examples of X-linked recessive disorders: Fragile X; Hemophilia; Muscular Dystrophy Examples of X-linked dominant disorders: Rett syndrome (very rare) The mother has 2 X chromosomes her ova will have either an unaffected gene OR an affected gene The father has one X and one Y chromosome his sperm will have either an X or a Y chromosome 300/330 - appleby

  5. Fragile X syndrome Common traits & symptoms: Mild to severe intellectual disabilities Emotional and behavioural problems What does it look like? https://public.ornl.gov/site/gallery/originals/ChromX.jpg A male child inherits an X from his mother and a Y from his father; if the X is fragile, he will be affected A female child inherits an X from her father and another X from her mother (who has 2 Xs) A girl (who has 2 Xs) may have one normal X and one fragile X; not likely to be affected If a girl inherits 2 fragile Xs, she will be severely affected 300/330 - appleby

  6. Females have an X chromosome from father and an X chromosome from mother; Males have an X and a Y chromosome

  7. Turner’s Syndrome &Klinefelter’s Syndrome Turner’s Syndrome: • affects 1 in 3000 girls • 1 (or part of one) of the X chromosomes is missing • only 45 chromosomes total Klinefelter’s Syndrome: • affects 1 in 700 boys • extra X chromosome (XXY) - 47 chromosomes 300/330 - appleby

  8. RECESSIVE PATTERN INHERITANCE Recessive pattern illnesses: sickle cell; Tay-Sachs; hemochromatosis; thalassemia; PKU; PKD Cystic fibrosis: defect in a gene located on chromosome 7 (https://public.ornl.gov/site/gallery/originals/Chrom07.jpg ) • pulmonary and gastrointestinal disease • if neither mother nor father have cystic fibrosis, they may still be carriers of 1 faulty gene • if only mother or father have 1 faulty gene, then no child will have cystic fibrosis; but child may still be carrier of disease 300/330 - appleby

  9. Recessive Inheritance 300/330 - appleby

  10. DOMINANT PATTERN INHERITANCE Dominant pattern illnesses: Marfan; neurofibromatisis; Alzheimer Huntington’s disease: a degenerative neurological disorder faulty gene on chromosome 4 (https://public.ornl.gov/site/gallery/originals/Chrom04.jpg) if mother or father have 1 faulty gene, she or he WILL develop Huntington’s disease – but not until age 40 – 50 if affected parent passes on faulty gene, then child will also be affected 300/330 - appleby

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  12. CHROMOSOMAL ABNORMALITIES Kinds of abnormalities: • part or all of a single chromosome may be missing • numerical abnormality - a sperm or ovum may have an extra chromosome (24) or lack a chromosome (22), e.g. Turner Syndrome • Extra chromosome material, e.g. Down Syndrome (Trisomy 21) [https://public.ornl.gov/site/gallery/originals/Chrom21.jpg ] • structural abnormality - rearrangement or loss of genetic material • e.g., deletions, duplications, inversions, ring formations and translocations of chromosome sections • Fragile X syndrome - a weakened or fragile site on the X chromosome [https://public.ornl.gov/site/gallery/originals/ChromX.jpg ] 300/330 - appleby

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  14. Examples of GeneticConditions & Diseases 300/330 - appleby

  15. Ethical Issues:Privacy and Confidentiality If you have a history of Huntington’s Disease in your family, should you have genetic testing to see if you will develop the illness? If you do have genetic testing, should you tell your siblings or partner the results of your testing? Should you be forced to submit to prenatal genetic testing before you decide to have children? YES NO UNDECIDED 300/330 - appleby

  16. Ethical Issues: Insurability If you are applying for life insurance, and you have a history of breast or ovarian cancer in your family, should you be compelled to have genetic testing for the BRCA1 or BRCA2 genes? If you have had this testing, must you tell the company? May they deny life insurance to you? Should life insurance companies have access to your genetic information? YES NO UNDECIDED 300/330 - appleby

  17. Ethical Issues: Employability Should an employer have the right to know your family history, including genetic disease, prior to offering you employment? Should an employer have the right to deny employment to someone with a susceptibility to a genetic condition? Should employers have access to your genetic information? YES NO UNDECIDED 300/330 - appleby

  18. Ethical Issues: Childbearing Should all pregnant women have prenatal testing? If a woman decides to continue a pregnancy involving a fetus with a genetic disorder, should she consider aborting the fetus? If she continues with the pregnancy, should she expect social supports in caring for an affected infant and child? YES NO UNDECIDED 300/330 - appleby

  19. Take another look at your list of genetic conditions & diseases: Which of these ethical issues would be of concern to a person with the genetic condition you have investigated: Privacy and Confidentiality Insurability Employability Childbearing What additional ethical issues or dilemmas might you expect to face if you were living with a diagnosed genetic condition? 300/330 - appleby

  20. Canadian Legislation – H of C BILL C-445: An Act to amend the Canadian Human Rights Act (genetic characteristics) Private Members Bill: Ms. Libby Davies 1st Reading on 1 October 2012 For all purposes of this Act, the prohibited grounds of discrimination are race, national or ethnic origin, colour, religion, age, sex, sexual orientation, genetic characteristics, marital status, family status, disability and conviction for which a pardon has been granted or in respect of which a record suspension has been ordered. http://www.parl.gc.ca/HousePublications/Publication.aspx?Language=E&Mode=1&DocId=6257497&File=4 300/330 - appleby

  21. Canadian Legislation - Senate BILL S-201: An Act to prohibit and prevent genetic discrimination Senator James Cowan; 1st Reading on 17 October 2013 This enactment prohibits any person from requiring an individual to undergo a genetic test or disclose the results of a genetic test as a condition of providing goods or services to, entering into or continuing a contract with, or offering specific conditions in a contract with the individual. Exceptions are provided for medical practitioners and researchers, as well as for insurance providers in respect of high-value insurance contracts if provincial laws expressly permit a requirement that existing genetic test results be disclosed. The enactment amends the Canada Labour Code to protect employees from being required to undergo or to disclose the results of a genetic test, and provides employees with other protections related to genetic testing and test results. It also amends the Canadian Human Rights Act to prohibit discrimination on the ground of genetic characteristics. http://www.parl.gc.ca/HousePublications/Publication.aspx?Language=E&Mode=1&DocId=6257111&File=19 300/330 - appleby

  22. Health insurance and 'genetic discrimination': Are rules needed? CARLY WEEKS The Globe and Mail Sunday, Jan. 01 2012 BrynneStainsby grew up knowing she had a good chance of being diagnosed with Huntington’s disease one day. Her father has the gene that causes the degenerative brain disorder, so she was born with one-in-two odds of developing it herself… While Dr. Stainsby, a Toronto chiropractor, … didn’t realize that simply coming from a family with a history of Huntington’s disease could disqualify her for life or disability insurance. As she was preparing to start her own practice, she learned that it would be extremely difficult, if not impossible, to get covered if she indeed had the genetic variant that causes the disease. 300/330 - appleby