Mendelian Genetics IV and V: Pedigrees and Sex Linkage

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  1. I.    Pedigrees
    a.    Collecting information about a family’s history for a particular trait and assembling this information into a family tree describing the __of parents and children across the generations
    b.    Important application of a pedigree is to help us calculate the probability that a future child will have a particular __
    • traits
    • genotype and phenotype
  2. II.    Sex Linkage
    a.    Chromosomal base for determining sex is simple
    i.    Two varieties of sex chromosomes
    1.    __
    a.    __smaller than __
    i.    Humans: __= female/ __= male
    2.    Small segments on end of Y are homologous with X, thus enabling behavior like homologous chromosomes during meiosis
    • X and Y
    • Y
    • X
    • XX
    • XY
  3. b.    Mammals
    i.    Two sex chromosomes segregate during __, and each gamete receives one
    1.    Each egg contains one __, while sperm may have __ or __
    ii.    In humans, anatomy of sex emerges about 2 months in
    • meiosis
    • X
    • X or Y
  4. c.    1990: British identified gene on Y chromosome required for development of __
    i.    __
    1.    Absent: __develop
    • testes
    • SRY: sex-determination region of Y
    • ovaries
  5. d.    Sequencing of Y
    i.    __genes that code for __proteins
    1.    Half expressed only in __, and some required for normal __functioning and production of normal __
    a.    A gene located on either sex-linked gene; those on Y are __
    i.    Y chromosome is passed along virtually intact from a father to all sons
    1.    Due to few Y-linked genes, few disorders transfer from father to son on Y
    • 78
    • 25
    • testis
    • testicular
    • sperm
    • Y-linked genes
  6. e.    Sequencing of X
    i.    1100 genes, which are __
    f.    Inheritance of X-Linked Genes
    i.    X have genes for many characters unrelated to sex
    1.    Fathers pass X-linked alleles to __but none to __
    2.    Mothers pass X-linked to both sons and daughters
    • X-linked genes
    • daughters
    • sons
  7. ii.    If X-linked trait recessive: female expresses phenotype only if __
    iii.    Because males have only one locus, __
    1. __
    a.    Far more males than females have __
    • homozygous for allele
    • heterozygous and homozygous don’t matter
    •    Once receiving recessive allele from mom= expressed
    • X-linked recessive disorders

  8. a.      Human X-linked disorders
    • Duchenne muscular dystrophy: affects 1/3500 males
    •                                                             ii.      Hemophilia
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Mendelian Genetics IV and V: Pedigrees and Sex Linkage

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