Chromosomal features,banding,classification

What are satellite chromosomes and NORs?

Chromosomes that have a small, separate segment (called a satellite)

Found on the short arms of acrocentric chromosomes (13, 14, 15, 21, and 22).

• Specific regions on satellite chromosomes that contain genes for ribosomal RNA (rRNA).

• Function: NORs direct the formation of nucleolus during cell division.

• These regions are highly repetitive DNA and are active during interphase

What is a secondary constriction?

A non-centromeric narrowing seen in some chromosomes (e.g. 1, 9, 16 on q arm),

often sites of rRNA gene transcription.

What is a fragile site?

Sometimes in certain regions of the chromosome chromatids "gaps”

example: FRAXA , causes Fragile X syndrome →inherited mental retardation.

Purpose of chromosomal banding?

Identifies homologous chromosomes and detects structural abnormalities.

Which group do sex chromosomes belong to?

X = Group C (metacentric)
Y = Group G (smallest, acrocentric, no satellites)