Chromosomes

ChromosomesChromosomes are strands of DNA

bound to proteins

Each cell has two sets of chromosomes, one from the mother and one from the father.

One Chromosome Identical copies

Centromere(joining point)

(The real thing)Coiled DNA

Homologous pairsThe members of a pair are referred to as homologous chromosomes. Each pair:

is the same size, has the joining point in the same

place, has the same gene loci in the same

sequence

A homologous pairHuman chromosome 9

Chromosome from mother

Chromosome from father

Deafness/hearing gene

Deafness/hearing gene

Chromosome numbers In humans there are 23 pairs of

chromosomes. One member of each pair comes from the mother, and one from the father.

Other species have different numbers.

Genome & karyotype Genome — this is the total of an

individual’s genetic material. A karyotype is a full complement of

chromosomes. It is usually shown as a drawing or photograph of stained chromosomes arranged in homologous pairs, from the biggest to the smallest.

E.g. Karyotype of a pig

Chromosomes of a human female

Chromosomes of a human male

DNA Structure DNA molecules are polymers of

nucleotides.= chains of nucleotide units

Nucleotides have 3 parts The 5 Carbon (pentose) sugar A phosphate group A base

Adenine, Thymine, Cytosine or Guanine

A simple model

A DNA molecule consists of two chains of nucleotides twisted around each other to form a double helix.

Alternating sugars and phosphates form the sides of the DNA “ladder”

The rungs are formed by the bases in complementary pairs. A – T and C – G

Here is the ladder

Let’s give it a twist to make the double helix

And this is a space-filling model of DNA

Packaging of DNA