Mendelian Inheritance Patterns S1M1

  1. Allele:
    different versions of a gene
  2. Gene:
    A unit of heredity in a living organism

    Is the region that produces a protein plus the promoter to make sure it can be produced
  3. Heterozygote:
    an individual with two different alleles at a given gene
  4. Homozygote:
    the two alleles are identical
  5. Hemizygote:
    has only one allele

    almost all X-linked genes are hemizygous in males
  6. Gamete:
    either egg or sperm, dependent on the sex of the person in which the meiosis occurs
  7. Phenotype:
    characteristics of a person, effects of genes + environment
  8. In a person heterozygous for a gene on Chr. 7, Meiosis will distribute the two alleles
    to two different gametes
  9. There is no such thing as a male hidden carrier in
    Sex linked diseases
  10. Autosomes are
    The chromosomes 1-22 excluding the sex chromosomes
  11. Dominant Disease are
    These are rare 1/500

    By chance alone, two heterozygotes rarely have children; one heterozygote + one homozygous normal is the rule

    Therefore homozygotes are extremely rare
  12. Fitness Definition:
    the number of offspring that reach reproductive age divided by the average number for the population
  13. Recessive Disease
    Only the homozygous carriers show symptoms (and homozygotes are rare)

    Normal occurrence is that patients are offspring of two heterozygous carriers

    New mutations are rare
  14. What are the pedigree symbols
    Image Upload 1
  15. Autosomal dominant inheritance:
    phenotype shows presence of allele also in heterozygote; gene on autosome (not X or Y)
  16. Autosomal recessive inheritance:
    phenotype only present when two bad alleles are present
  17. Individuals with a Recessive normally don't have
    have affected parents; average of ¼ affected in each sibship; the parents are often related (sometimes quite distantly)
  18. Individuals with a Dominant disease all have
    one affected parent (except new mutations and reduced penetrance); average of 50% affected in a sibship
  19. Autosomal diseases are found to be:
    In equal number of affected males and females (except sex limited)
  20. Sex-linked Inheritance X-linked recessive:
    Express the phenotype if there is no other allele present, i.e., in hemizygous males [or homozygous females]
  21. Sex-linked Inheritance with an X-linked dominant:
    always shows phenotype
  22. Y-linked phenotypes have shown to express
    male fertility; reports of non-syndromic hearing impairment
  23. In X-linked recessive is expressed normally with
    many more males than females affected; never father-to-son transmission

    New mutations happen
  24. In an X-linked dominant circumstance:
    more females than males affected; never father-to-son transmission
  25. Y-linked individuals are only transmitted what way
    Only father-to-son transmission
  26. Transmission of X-linked Traits chart
    Image Upload 2
  27. Sex-limited Inheritance charecteristics
    • This is not the same as Sex-linked!
    • Genes on autosomes
    • Can be dominant or recessive
    • Typically influences traits expressed in one sex only or traits influenced by the sex hormones
  28. What are some examples Sex-limited Traits
    • Male pattern baldness
    • Autosomally inherited infertility
    • Milk-related traits
    • Breast and ovarian cancer
    • Testicle cancer
  29. Penetrance of a disease-causing mutation is
    The proportion of individuals with the mutation who exhibit clinical symptoms

    A non-penetrant person is one who has the predisposing genotype but does not show symptoms
  30. Reduced Penetrance used to only occur in dominant diseases
    But now similar observations have been found in recessive diseases
  31. Variable Expressivity
    Difference in severity or in age of onset for seemingly identical genotype (mostly seen in dominant diseases)
  32. Heterogeneity
    • Similar -> identical phenotype, but:
    • Causes can be involvement of different loci (locus heterogeneity)
    • Or involvement of different alleles at the same locus (allelic heterogeneity)
  33. Allelic heterogeneity can mean
    different alleles at the same locus produce different diseases
  34. Phenocopies:
    looks like a known genetic disorder, but is caused by environmental influence
  35. Pleiotropy:
    mutation in one gene has more than one effect, effects in more than one physiological system
  36. Contiguous gene disorders:
    Typically in deletion or duplication of part of a chromosome
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Mendelian Inheritance Patterns S1M1