The Normal Human Karyotype

Somatic cells

metaphase

X-inactivation

are responsible for secondary sex characteristics

Chromosomes arranged in pairs from largest, most metacentric to the smallest most acrocentric

centromere is in the middle of the chromosome

One chromosome arm is longer than the other

short arm

long arm

• centromere is at one end
• the short arm consists of heterochromatin and nucleolar organzing region
• may be variable in size and staining patterns

the centromere- typicalled associated satellite DNA ( alpha-satellite)

• Consists of highly repetitive sequences that are either inert or NOR (nuclear organizing region)
• stain lighter

• Functional DNA sequence TTAGGG
• prevents chromosomes ends from sticking to each other

a genetically inert piece of chromosome usually connected to the short arm of acrocentric chromosome via a secondary constriction , the NOR and highly repetitive DNA sequences

• Cross striation patterns on chromosomes due to various treatments
• reflect underlying DNA sequences and chromosome structure

• T-lymphocytes
• phytohemaglutinin

Brings t-lymphocytes to an actively dividing state

Hypotonic

• Methanol and acetic acid
• preserves nucleoprotein structure and clears cytoplasm

• the first banding technique
• uses a special fluorescent microscope

produces banding patterns after gentle treatment with trypsin followed by staining with Giemsa

Stains heterochromatin around the centromeres of every chromosome and secondary constrictions of 1, 9 and 16

Stains nucleolar organizer regions on acrocentric human acrocentric chromosomes

Early or late DNA replication patterns when subsituted for thymidine in early or late S period

When substituted for thymidine through two complete cell cycles produces differential staining of sister chromatids and reveals sister-chromatid exchanges (SCEs)

• Heat treatment
• high salt concentration
• Is the reverse pattern of G banding