Lecture Notes on Chromosomes and Karyotypes

Misconceptions About Chromosomes

• Chromosomes are often depicted in diagrams as X-shaped which can lead to misconceptions:
  • Chromosomes do not always look like letters (X, Y).
  • Chromosomes can appear as single stick structures.
• Misunderstandings about the number of chromosomes:
  • Humans have 46 chromosomes that replicate during cell processes.
  • Concerns about damaging chromosomes due to a limited number.

Structure and Function of Chromosomes

• Chromatin Composition
  • Chromosomes are composed of chromatin, which is made of DNA and proteins.
  • DNA is wrapped around proteins called histones forming nucleosomes (bead-like structures).
  • Further packing is necessary for DNA to fit into the nucleus and facilitate cell division (mitosis).
• Chromosome Packing and Unpacking
  • Highly packed during certain cell stages for replication and division.
  • Needs to be unwound during DNA replication.
• Human Chromosomes
  • Represented as single units or duplicated with centromeres joining chromatids.
  • 46 chromosomes in humans, doubling of chromatids occurs in interphase.
  • During mitosis, chromatids are separated into daughter cells.

Karyotypes and Chromosome Analysis

• Karyotype
  • A visual representation of chromosomes, typically taken during metaphase.
  • Chromosomes are stained and visible with two sister chromatids each.
• Homologous Chromosome Pairs
  • 23 pairs of chromosomes: 22 autosomes, 1 sex chromosome pair.
  • Autosomes are not related to biological sex but influence traits like eye color, height.
• Sex Chromosomes
  • Females: XX, Males: XY.
  • Father’s sperm determines the sex of the offspring.

Importance of Chromosome Study

• Genetic Disorders
  • Karyotypes reveal abnormalities like missing or extra chromosomes.
• Career Opportunities
  • Expanding field of genetics, potential careers in genetic counseling.