Chromosomal Inheritance+ Pedigrees

Chromosomes

  • In humans

    • sex chromosomes: x and y (1 pair)

    • autosomes: other 44 chromosomes (22 pairs)

Meiosis + Nondisjunction

  • meiosis normally creates haploid gametes

  • nondisjunction: failure of homologous chromosomes or sister chromatids to seperate properly

    • creates gametes and offspring w/ 1+ or 1- chromosomes

  • euploid: contains 2n chromosomes

    • “Eu”= true

  • Aneuploid: contains (2n-1) or (2n+1) chromosomes

    • an = not

    • (2n-1)= monosomy: missing a copy of a chromosome

    • (2n+1) = trisomy: has a third copy of a chromosome

  • Fertilization w/ an aneuploid gamete leads to aneuploid offspring

Pedigrees

  • A family tree showing the traits of parents and children across generations

  • symbols:

    • females: circles

    • males: squares

    • unaffected (don’t have trait): unshaded

    • affected (have trait): shaded

  • Autosomal reccesive pedigree

    • gene: on an autosome

    • inherited trait: recessive

      • unaffected- AA or Aa

        • Aa= carrier

      • affected- aa

      • hints:

        • parents w/o the trait can have a kid with it

        • seems to “skip” a generation

  • Autosomal dominant pedigree

    • gene: on an autosome

    • inherited trait: dominant

      • unaffected- aa

      • affected- AA or Aa

        • Hints:

          • kids w/ the trait must have at least 1 parent w/ it

          • doesn’t skip a generation

  • X linked recessive pedigrees

    • gene: on x chromosome

    • inherited trait: recessive

      • unaffected:

        • XB XB and XB XB

        • XB Y

      • affected

        • Xb Xb

        • Xb Y

      • hints:

      • no heterozygous males

      • effected mother- affected sons

      • more common in males

      • can also skip generations

  • X linked dominant pedigrees

    • gene: on x chromosome

    • inherited trait: dominant

      • unaffected-

        • XbXb

        • Xb Y

      • affected-

        • XBXB and XBXb

        • XB and Y

    • hints:

      • no heterozygous males

      • kids w/ it must have a parent w/ it

      • affected father- affected daughters

  • Mitochondrial Inheritance

    • gene: on mito. DNA (mt. DNA)

    • inherited trait: neither dom. nor rec. b/c no homol. chrom.

    • people just either inherit the mutation or not

      • hints:

        • always passed mother all offspring only

        • never passed father- offspring

        • in a pedigree either all or none of the offspring are affected