chromosomal basis of inheritance
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Chromosomal Basis of Inheritance. Chapter 15. Objectives. Understand the concept of “Linked Genes” Understand how recombination of genes affect genetic variability Understand how frequency of recombination of linked genes is related to their loci distance from one another

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Presentation Transcript
objectives
Objectives
  • Understand the concept of “Linked Genes”
  • Understand how recombination of genes affect genetic variability
  • Understand how frequency of recombination of linked genes is related to their loci distance from one another
  • Be familiar with patterns of inheritance for genes on sex chromosomes
  • Be familiar with errors that may occur in chromosomal inheritance due to problems associated with meiosis
linked genes
Linked Genes
  • Linked genes are those that reside on the same chromosome and tend to be inherited together
    • Autosomal genes reside on the autosomal chromosomes (pairs 1-22)
    • Sex-linked genes are found on the sex chromosomes (pair 23, usually on the X)
recombination of genes
Recombination of Genes
  • Production of offspring with a new combination of traits is called genetic recombination
  • Independent assortment may recombine genes that are unlinked
  • Linked genes can become unlinked through recombination events like crossover (during meiosis)
gene mapping
Gene Mapping
  • Maps of genes on chromosomes can be constructed from recombination data
  • Recombination data for linked genes reflects the “distance” of the 2 loci from one another
  • The farther apart 2 loci are from one another the more frequent the observed recombination due to crossover

Linkage map: genetic map

based on recombination

frequencies

sex linked inheritance
Sex Linked Inheritance
  • Males and females differ in their sex chromosome combination (females XX; males XY)
  • Barr bodies
  • Because the X contains genes and the Y “does not”, inheritance patterns of sex-linked genes vary between the sexes
    • recessive traits more prevalent in males
errors in inheritance
Errors in Inheritance
  • Genetic disorders can occur due to:
    • changes in chromosome number
      • nondisjunction
    • changes in gene sequence
      • deletion
      • duplication
      • inversion
    • changes in gene location
      • translocation
nondisjunction
Nondisjunction
  • Failure of a pair of chromosomes to separate during gamete formation
  • Genetic disorders like:
    • Down’s syndrome (#21, 3n)
    • Turner syndrome (XO)
    • Metafemale (XXX)
    • Kleinfelter Male (XXY)
    • Jacob’s Male (XYY)
changes in gene sequence
Changes in Gene Sequence
  • Deletion: loss of a chromosomal segment
  • Duplication: addition of a chromosomal segment
  • Inversion: flipping of information on a chromosome
changes in gene sequence1
Changes in Gene Sequence
  • Translocation: the movement of information from one member of a homologous pair to a chromosome of a different (non homologous) pair
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