CHROMOSOME

📖 What is a Chromosome?

A chromosome is a thread-like structure made of DNA and proteins, found in the nucleus of every living cell.
Chromosomes carry genes, which contain the instructions that tell our bodies how to grow, develop, and function.

🧠 Key Facts:

• Humans typically have 46 chromosomes, arranged in 23 pairs.

• Each parent contributes 23 chromosomes to their child.

• Chromosomes ensure that DNA is accurately copied and distributed during cell division.

🕰️ Discovery History:

🔹 1870s – Walter Flemming (Germany):

• First observed thread-like structures in dividing cells using a microscope.

• Described chromatin, which later was understood to be chromosomes.

🔹 1888 – Term "Chromosome":

• Coined by German anatomist Heinrich Wilhelm Waldeyer-Hartz.

• From Greek: chroma = color, soma = body (because chromosomes absorb stain well under a microscope).

🔹 1902 – Chromosome theory of inheritance:

• Proposed by Theodor Boveri and Walter Sutton.

• They linked Mendel’s laws of inheritance to the behavior of chromosomes.

🔬 Structure of a Chromosome:

When a cell divides, chromosomes become visible under a microscope as X-shaped structures.

👨‍👩‍👧‍👦 Types of Chromosomes in Humans:

1. Autosomes (1–22 pairs)
   – Control body functions and traits.

2. Sex Chromosomes (23rd pair):
   – XX = Female
   – XY = Male
   – Determine biological sex and some sex-linked traits.

🏥 Medical Relevance of Chromosomes:

1. Chromosomal Disorders:

• Occur when there is a missing, extra, or damaged chromosome.

• Examples:

  • Down Syndrome → Extra chromosome 21 (Trisomy 21)

  • Turner Syndrome → One X chromosome missing (XO)

  • Klinefelter Syndrome → Extra X in males (XXY)

2. Cancer and Chromosomes:

• Some cancers are linked to chromosomal mutations (e.g., Philadelphia chromosome in leukemia).

3. Prenatal Testing:

• Tests like karyotyping or amniocentesis check for chromosomal abnormalities in unborn babies.

4. Gene Therapy & Genetic Engineering:

• Target chromosomes to fix or replace faulty genes.

🧾 Quick Recap Table: