Pedigree Analysis: A Guide to Understanding Inheritance Patterns, Assignments of Construction

shown and analyzed in pedigrees. – pedigrees are formalized ways using standard sets of symbols to depict family trees and lineages.

Typology: Assignments

2021/2022

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Pedigree Analysis
(cf. chapters 4.4, 5.2, 6.2 of textbook)
“crosses” and “matings” in human(s) (families) are
shown and analyzed in pedigrees
pedigrees are formalized ways using standard sets of symbols
to depict family trees and lineages
pedigrees provide concise and accurate records of families
pedigrees are helpful in following and diagnosing heritable
traits (e.g. diseases and medical conditions), i.e. describing
patterns (or modes) of inheritance
pedigrees are useful in mapping (locating and isolating) genes
“responsible” for certain traits (will be covered later)
pf3
pf4
pf5
pf8
pf9
pfa

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(cf. chapters 4.4, 5.2, 6.2 of textbook)Pedigree Analysis

• “crosses” and “matings” in human(s) (families) areshown and analyzed in pedigrees

  • pedigrees are formalized ways using standard sets of symbolsto depict family trees and lineages
  • – pedigrees provide concise and accurate records of familiespedigrees are helpful in following and diagnosing heritable

traits (e.g. diseases and medical conditions), i.e. describingpatterns (or modes) of inheritance

  • pedigrees are useful in mapping (locating and isolating) genes“responsible” for certain traits (will be covered later)

Pedigree Construction

  • use standard set of symbols (cf.figure 4.13 of textbook)
  • one generation per row (oldestat the top)
  • siblings are shown in order ofbirth (from left to right)
  • generations are given romannumerals (I, II, III, IV, etc.)
  • individuals within a generation(row) are given arabic numerals
  • (1, 2, 3, 4, etc.)(show overhead)

normal female normal male female with trait male with trait sex unspecified male, carrying allelefor trait but does not express it (“carrier”) etc. etc. etc.

autosomal recessive

• • both sexes affected (males and females)trait can skip generations

• e.g. cystic fibrosis, albinism (cf. figure 4.15 of textbook)

I

II

III

IV

autosomal dominant

  • • both sexes affected (males and females)trait does NOT skip generations
  • e.g. myotonic dystrophy, hypotrichosis (hair loss that begins inchildhood; cf. figure 4.16 of textbook)

I

II

III

IV

X chromosome linked dominant

I

II

III

IV

  • • both sexes affected (males and females)females transmit to daughters and sons
  • • males ALWAYS transmit to daughters, but NOT AT ALL to sonstrait does NOT skip generations
  • • e.g. Rett Syndrome (mental retardation, neural degeneration)cf. chapter 6.2 of textbook

Y chromosome linked

I

II

III

IV

• • only males are affectedmales ALWAYS transmit to sons

• cf. chapter 6.2 of textbook

gender effects on phenotype

(cf. chapter 6.4 of textbook)

  • sex-limited inheritance (e.g. traits affected by hormones) – only one gender is capable of showing trait, the other gender
    • is NOT, regardless of underlying genotypethe genes involved are typically autosomal, but the

expression of these genes is dependent on the gender of theindividual

  • sex-influenced inheritance (e.g. traits affected by hormones)^ –^ e.g. beard growth, breast size
    • the gender of the individual determines whether a particularphenotype assumes dominant or recessive state
      • e.g. a phenotype that is dominant in one gender isrecessive in the other gender
    • e.g. pattern baldness (dominant in males and recessive infemales)

problems in constructing a pedigree

  • • poor medical recordsscattering of family members
  • • inaccurate and anecdotal informationmiscarriages and still births
  • • infidelity / concealed adoptionsvariable expressivity of genotype (as phenotype)
  • incomplete penetrance of genotype (showing phenotype)
  • AGAIN: pedigrees can frequently rule out, but notnecessarily prove, a certain mode of inheritance