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Chromosomal Basis of Inheritance

Chromosomal Basis of Inheritance

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Chromosomal Basis of Inheritance

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Presentation Transcript

  1. Chromosomal Basis of Inheritance Chapter 15

  2. 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

  3. 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)

  4. Recombination • 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)

  5. 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

  6. 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

  7. 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

  8. 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)

  9. Changes in Gene Sequence • Deletion: loss of a chromosomal segment • Duplication: addition of a chromosomal segment • Inversion: flipping of information on a chromosome

  10. 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

  11. That’s all folks!!