Download Genes, Chromosomes, and DNA

SBI 3U
January 7th, 2012
Packaging of DNA
 Chromatin, a combination of DNA and protein
 During cell division, DNA compacts into structures
called chromosomes
 Chromosome – condensed DNA, can contain 100s1000s of genes!
Fun Fact: A human body cell contains enough DNA to
stretch about 2 m in length!
Chromosomes
 Diploid number
 1 homolog of each pair from each parent
Extreme Chromosomes!
 Radiolarian – 1600 chromosomes
 Roundworm – 2 chromosomes
DNA in Chromatin
 Tightly coiled around proteins called histones
 Nucleosomes
Discovery of DNA structure
 Early 1950s – Rosalind Franklin discovered that DNA
had the form of a spiral or helix
 Used x-ray crystallography
Discovery of DNA structure
 James Watson and Francis Crick used Franklin’s
findings and added to it
 Watson & Crick’s model: sugar-phosphate backbone
on outside and subunits called nitrogenous bases on
the inside
The Components of DNA
 Long chain of subunits called nucleotides
 A nucleotide has 3 parts:
1. deoxyribose
2. A phosphate group
3. A nitrogeneous base; a single or double ring of
carbon and nitrogen atoms
The Components of DNA
 4 types of nucleotides in DNA –
only differ in their nitrogeneous
bases: adenine, guanine, thymine
& cytosine
 Thymine & Cytosine are
pyrimidines
 Adenine & Guanine are purines
 Arrangement of nucleotides in
DNA stores information -- genes
Chromosomes
 Within the karyotype, there is one pair of
chromosomes that are not identical in shape and size:
sex chromosomes
 Female: XX
 Male: XY
 22 pairs are autosomes
Sex Linkage
 Discovered by Thomas Hunt Morgan
 Any gene located on a sex chromosome is called a sex-
linked gene
 X-linked genes: genes on X chromosome
 Color blindness & hemophilia
Sex-Linked Disorders
 Hemophilia: bleeder’s disease
 Bloodlines of royal British family