BIOL 310 - Ch 6 Lecture Notes

  • pedigree & pedigree conventions

    • a pictorial representation of a family history outlining the inheritance of one or more traits

  • autosomal recessive disorders

    • must have two homozygous alleles to be affected

    • can occur equally in males and females (no sex bias)

      • these disorders skip generations

      • considered rare because the carriers of genes permit a 25% chance of having an affected offspring

    • few individuals are affected & offspring have parents that usually unaffected

  • autosomal dominant disorders

    • appears equally in males & females

    • affected people have at least one affected parent

      • unaffected individuals do not transmit the trait

      • more individuals are effected

  • family hypercholesterolemia

    • dominant disorder

    • variety of genotypes & phenotypes

      • DD leads to death at young age

      • Dd leads to high LDL

      • dd leads to normal LDL

    • receptor on surface of the cell that brings LDL into the cell & removes it from the bloodstream

      • mutated form means you cannot remove LDL as readily which can lead to plaque buildup in the blood vessels

  • X-linked recessive

    • males are often affected

      • the trait is not passed onto sons

      • creates carrier daughters

    • females are rarely affected since it must be homozygous recessive

      • produces affected sons

    • the trait skips generations (in direct linage)

  • X-linked dominant trait

    • do not skip generations

    • affected males pass the trait to all of their daughters

    • affected females pass the trait on to nearly half of their sons and daughters

  • Y-linked dominant trait

    • appears only in males

    • all male offspring of an affected male are affected

  • issues associated with human pedigrees

    • long generation time

      • few genes in degree

    • few offspring

      • weak stats

      • low predictive power

    • solution — twin studies

      • monozygotic twins (identical)

      • dizygotic twins (fraternal)

      • concordance: proportion of twin pairs where both twins are in accordance with each other (either both affected or both unaffected)

        • indicates strong or weak heritable components

        • higher value in monozygotic than dizygotic means there is strong heritable components

    • for environmental studies, comparing difference between factor of interest for biological parents vs adoptive parents

      • for BMI, the more obese the biological parents, the more obese the offspring are likely to be

      • inverse is true for adoptive parents — as the parent becomes more obese, the kid becomes more thin

      • obesity has a strong genetic component instead of environmental impacts

  • genetic disorders

    • information overload exacerbated by companies like 23 & Me that market their database (or whatever) to give you reports on your personal genetics

    • detection of disorders causes questions

      • tests are readily available to close this gap of knowledge given that the reports handed back are not easy to instantly recognize what means what

  • genetic counselling

    • the process of helping people understand and adapt to the medical, psychological and familial implications of genetic contributions to disease

    • this involves interpretation of family and medical history to assess the chance of disease occurrence or reoccurrence

    • education about inheritance, testing, management, prevention resources, and research

    • promoting informed choices and adaptation to the risk or condition

  • reasons for genetic counselling

    • a person knows of a genetic disease in the family

    • a couple has given birth to a child with a genetic disease, birth defect or chromosome abnormality

      • the kid becomes the proband for the trait of interest

    • a couple has a child who is intellectually disabled or has a close relative who is intellectually disabled

    • an older women becomes pregnant or wants to become pregnant

      • risk of conceiving at an older age leading to more issues

    • husband & wife are close related (e.g. first cousins)

    • a couple experiences difficulties achieving a successful pregnancy, infertility, etc

    • a pregnant women is concerned about exposure to an environmental substance that causes birth defects

    • a couple need assistance in interpreting the results of a prenatal or other test

    • both prospective parents are known carriers for a recessive genetic disease or both belong to an ethic group with a high frequency of a genetic disease

  • more reason for genetic counselling — most “updated”

    • direct-to-consumer testing

    • pre-symptomatic testing

    • pharmacogenetic testing