Chapter 12 ~ BIO101

Grading and Exam Review

  • Exam Handout: Final exam printout may show slight discrepancies in points. Check Canvas for official grades.
  • Exam Review: Review your exam in class Monday; bring your printout.
  • Office Hours: Students can review exams during office hours for a detailed understanding.

Chapter 12 Overview

  • Notes Packet: Complete notes from chapter 12 will be used for ongoing class activities.
  • Withdrawal Date: Withdrawal from the course is on Wednesday, the 23rd. Consider all factors before deciding.

Genetic Concepts

  • X Inactivation: One X chromosome in XX individuals is inactivated; creates a Barr body.
    • Purpose: Balances gene dosage between XX (female) and XY (male) individuals.
  • Example: Calico cats exhibit orange and black fur because of X inactivation.
    • The color is determined by which X chromosome is active in each area of fur.
  • Questions on Calico Cats:
    • Orange fur = active X; Black fur = Barr body (inactive X).

Linked Genes vs. Independent Assortment

  • Independent Assortment: Genes on different chromosomes assort independently.
    • Results in four possible gametes.
  • Linked Genes: Genes located close together on the same chromosome.
    • Fewer gamete combinations, typically two types, if no crossing over occurs.
  • Mapping Linked Genes: Understanding recombination frequencies helps determine distances between linked genes.

Nondisjunction and Aneuploidy

  • Aneuploidy: Abnormal chromosome number due to nondisjunction during meiosis.
    • Trisomy: One extra chromosome (e.g., Down syndrome, trisomy 21).
    • Monosomy: One missing chromosome (e.g., Turner syndrome, X0).
  • Nondisjunction Types:
    • Meiosis I: Creates gametes with n+1 and n-1 chromosomes.
    • Meiosis II: Results in n+1, n-1, and normal gametes.

Mitochondrial Inheritance

  • Mitochondria: Have their own DNA; inherited maternally from the egg cell.
  • Endosymbiotic Theory: Suggests mitochondria and chloroplasts originated as independent prokaryotes.