Lecture on Chromosomes and Karyotypes

Introduction

• Chromosomes are often misrepresented as always being X-shaped.
• Misconception: People have 2 X or an X and a Y chromosome, leading to confusion.
• Purpose of lecture: To clear up misconceptions about chromosomes.

Chromosomes Basics

• Chromatin: Composed of DNA and protein.
• Histones: Proteins around which DNA is wound, forming nucleosomes ("beads on a string").
• Chromosomes are highly packed structures to fit DNA in the nucleus and for cell division (mitosis).

Eukaryotic Chromosomes

• Human Chromosomes: Consist of 46 chromosomes.
• DNA Replication: DNA unwinds for replication. Chromatin packing varies based on factors.

Chromosome Structure

• Single Component vs. Replicated Chromosomes:
  • Single chromosome vs. replicated (bound at centromere).
  • Centromere isn't always in the center.
  • During interphase, chromosomes duplicate but are counted as one chromosome until separated.

Chromosome Counting

• Humans: 46 chromosomes, duplicate to 92 chromatids during mitosis.
• Chromatids are pulled apart to ensure each cell ends up with 46 chromosomes.

Gene Expression

• Gene activity varies by cell type (e.g., eye cells vs. stomach enzymes).
• Chromatin packing affects gene accessibility.

Karyotype

• Definition: An image of chromosomes, often used for medical screenings.
• Chromosomes are stained and observed during mitosis, particularly metaphase.
• Homologous pairs are arranged in a karyotype (23 pairs in humans).

Human Chromosome Pairs

• Autosomes: 44 of the chromosomes (22 pairs), unrelated to biological sex.
• Sex Chromosomes: Determine biological sex (XX female, XY male).
  • Father determines the biological sex.

Significance of Karyotypes

• Useful for identifying genetic disorders.
• Missing or extra chromosomes can be detected.

Careers Related to Genetics

• Field of genetics is expanding.
• Genetic counseling is a potential career path.

Conclusion

• Understanding chromosomes and karyotypes is crucial for genetics.
• Encouragement to explore further studies in genetics.