By Ajinkya M Kadu M.Sc. - 1

What are Chromosomes?

Size

Shape

Structure

Centromere

Structure of X & Y chromosome

Chromosomes : Chroma – color, soma – body

Found in Nucleus of CellAbility of Self replicationRole in – heredity, variation,

mutation & evolution

CHROMOSOMES

• Morphologically & genetically identical Chromosomes are called Homologous chromosomes.

Euploidy – Presence of whole sets of Cromosomes

Number of Chromosomes

Example

Chromosome No. in Different animals

Varies from species to species

Normally 0.1 to 33 um in length

0.2 to 2 um in thickness

Size

Depends on stage of Cell Division

In Interphase = less condensed

In Metaphase = max. condensation & appear short

Shape

Metaphasic chromosome has 2 identical halves called Sister chromatids

Each chromatid is in turn made up of sub-chromatids called chromonemata

Both arms are joined at Centromere

Structure

Centromere is also called the Primary constriction

During cell division spindle Fibres are attached at centromere

After primary constriction, secondary constriction is present

The part of the chromosome beyond the nucleolus is called satellite

Centromere

Tip of chromosome is called Telomere

It prevents sticky ends of chromosome from attaching

The surface of a chromosome bears number of small swellings called chromomeres.

Types of Chromosomes

• X chr is longer than Y chr• X chr contains < Euchromatin & >

Heterochromatin • Y chr contains > Euchromatin & <

Heterochromatin • X and Y chromosomes show

homologous & Non-Homologous regions.

Structure of X & Y chr

REFRENCE

• Human Chromosomes by Orlando J. Miller

• Chromosome biology by R. Appels

• http://www.chromodisorder.org/CDO/

• http://www.genome.gov/26524120

• http://www.youtube.com/watch?v=zf7tbymrv9 o

• http://www.johnkyrk.com/chromosomestructu re.html