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Understanding Pedigrees: Autosomal and Sex-Linked Traits in Human Inheritance

This guide explores the use of pedigrees as a tool for tracking the inheritance of specific traits in families. We illustrate how to identify whether traits are autosomal dominant, autosomal recessive, or sex-linked, using symbols to denote affected and unaffected individuals. Detailed examples, including the hereditary patterns of albinism and hemophilia in royal families, highlight critical inheritance concepts. Learn to determine genotypes employing logical reasoning with provided case studies.

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Understanding Pedigrees: Autosomal and Sex-Linked Traits in Human Inheritance

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  1. Pedigrees and Human Inheritance SBI3U

  2. Pedigrees • Family trees used by scientists to track the inheritance of certain traits • Useful for determining whether a trait is autosomal or sex-linked • Symbols Used: Affected Unaffected Mating Siblings Male Female Sex unspecified

  3. Pedigrees • The following is an example of a pedigree where some members of the family display an autosomal dominant trait • Determine the genotypes using logic • Roman numeral refers to the generation • Number refers to the individual in the generation I – 1 = GR___ I – 1 = GRGr I I – 2 = GrGr 1 2 II – 1 = GrGr II II – 2 = GR___ II – 2 = GRGr 1 2 3 II – 3 = GrGr

  4. Autosomal Inheritance • Autosomal Dominant • Can tell if a trait is autosomal dominant if: • Both parents are affected by the trait but they have a child who isn’t I 1 2 II 1 2 3

  5. Autosomal Inheritance • Autosomal Recessive • Can tell if a trait is autosomal recessive if: • Both parents are unaffected by the trait but they have a child who is I 1 2 II 1 2 3

  6. Albinism • Determine whether or not albinism is autosomal dominant or recessive • Determine the genotypes of all individuals PNPa PNPa PNPa PNPa I 1 2 3 4 II 1 2 3 4 5 6 PN? PN? PaPa PaPa PaPa PN? III 1 2 3 PNPa PNPa PNPa

  7. Sex-Linked Traits • Some traits are coded for on the X or Y chromosomes • This leads to some interesting heredity • X – linked: coded for on the x-chromosome • Red – Green colour blindness and male-pattern baldness • X – linked traits are disproportionately displayed in males • Y – linked: coded for on the y-chromosome • Reduced fertility • Fewer traits are y-linked since y contains fewer genes than x

  8. Sex-Linked Traits • X – linked recessive • Traits passed down from mothers, most frequently to their sons • Many more males will display the phenotype than females I 1 2 3 4 II 1 2 3 4 5 6 III 1 2 3

  9. Sex-Linked Traits • Y – linked recessive • Traits passed down from fathers to sons. No females will be affected I 1 2 3 4 II 1 2 3 4 5 6 III 1 2 3

  10. Hemophilia in the Royal Family Hemophilia is a sex-linked trait where the affected individual has difficulty forming blood clots

  11. Hemophilia in the Royal Family Hemophilia is a sex-linked trait where the affected individual has difficulty forming blood clots XY XhX I XhX II XhX XY XY XhY X_ III XY XhY XhY XhY IV XY XhY

  12. Homework Pg 201 #1-5

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