Chromosomal Basis of Inheritance

Announcements

  • Attendance: Check in using iClicker or submit an index card with name, date, and responses to today’s questions.
  • Upcoming Exam: Exam 4 on Thursday, July 25 covering Chapters 15 (last part), 16, 17, 18, 22, 23, & 24.
  • Today's Focus: Discuss end of Chapter 15 and start Chapter 16.
Homework Bonuses
  • Arizona State University Survey: Due April 16 at 11:30 PM (2 exam points)
  • Miracle of Life Video/Worksheet: Due April 20 at 11:30 PM (2 exam points)
  • Biology Café Survey: Due date TBD (2 exam points)
  • UAB IDEA Survey: Due date TBD (if 75% complete, a final exam question will be given in advance)
  • Online Pearson Homework (Chapters 16 & 17): Due April 20 at 11:30 PM
  • Online Quizzes for Chapter 16: Due April 22 at 12:30 PM
  • General Note: Study for final exam.

Chapter 15: The Chromosomal Basis of Inheritance

Learning Objectives
  • Mendel’s Laws of Inheritance: Discuss their relevance to chromosome behavior during meiosis and fertilization.
  • Morgan's Experiments: Explain findings with red and white-eyed fruit flies, establishing the idea of sex-linked traits.
  • Inheritance Patterns of Sex-Linked Genes: Describe patterns and effects of X inactivation in female mammals.
  • Gene Linkage and Crossing Over: Explain their impact on inheritance.
  • Chromosomal Alterations: Identify types and consequences, linking to genetic disorders.
  • Non-Mendelian Inheritance Patterns: Highlight organelle genes and imprinted genes.
Sex-Linked Genes
  • A sex-linked gene is located on sex chromosomes.
  • Two types:
    • Y-linked genes: Few in number.
    • X-linked genes: Numerous and often crucial for various body traits.
Inheritance of X-Linked Genes
  • X chromosomes carry many unrelated traits, whereas Y-linked genes are primarily gender-related.
  • Inheritance Patterns:
    • Females need two copies of a recessive X-linked trait (homozygous).
    • Males only need one copy (hemizygous) for expression.
  • X-linked disorders are more common in males due to lack of a second X to mask recessive alleles.
X Inactivation in Female Mammals
  • Females have two X chromosomes, but one becomes inactivated during embryonic development, forming a Barr body.
  • As a result of this inactivation, females can exhibit mosaic expression of X-linked traits if heterozygous.
Linkage and Inheritance
  • Thomas Hunt Morgan's studies with Drosophila demonstrated that genes can be linked.
  • Using traits of body color and wing size, Morgan noted that specific combinations of traits tended to be inherited together, suggesting they are on the same chromosome.
Alterations of Chromosome Structure
  • Types of Alterations:
    • Deletion: Segment removal.
    • Duplication: Segment duplication.
    • Inversion: Segment orientation reversal.
    • Translocation: Segment moved to another chromosome.
Genetic Disorders Due to Alterations
  • Alterations of chromosome number:
    • Down syndrome (Trisomy 21)
    • Klinefelter syndrome (XXY)
    • Turner syndrome (X0)
  • Alterations of structure:
    • Cri du chat syndrome (deletion in chromosome 5)
    • Chronic myelogenous leukemia (translocation)
Non-Mendelian Inheritance Patterns
  • Organelle Genes: Found in cytoplasmic organelles like mitochondria and chloroplasts, and are maternally inherited.
  • Genomic Imprinting: Certain traits exhibit expression depending on the parental origin of the allele, suggesting a parent-of-origin effect.