3.2: Chromosomes

Prokaryotes

One chromosome (single copy of each

gene).

DNA is not associated with proteins (naked).

Plasmids are present in prokaryotes in MOST

cases.

Plasmids

Typically only found in prokaryotes

Contain some useful DNA e.g. genes for antibiotic resistance

Can easily transferred between cells – even between species.

Scientific research takes advantage of these traits.

Eukaryotes

DNA is linear

A long single strand

Beads on a string

Each bead is a nucleosome

A nucleosome is DNA wrapped around 8

histones.

DNA has negative charge, histone is

positive.

DNA becomes condensed/supercoile

d. Forming chromosomes.

Nucleosome

Nucleosome is a fairly large complex of

8 proteins and 146 nucleotides-long DNA.

Chromosome terminology

1. Telomere

2. Centromere

3. Short chromatid

4. Long chromatid

Task

1. What is the Human genome project? Dates? Aims? Findings?

2. What were the techniques used in the project?

3. Where did the material come from? Ethical considerations?

4. Who ‘controls’ this information? How should/could it be used?

5. Junk/satellite DNA, what? Why?6. Future applications of this research?

The Human Genome.

The complete sequence of Human DNA.

Genome of eukaryotes has lots of highly repetitive sequences. (5-45% of total genome). Between 5 – 300 base pairs per repetitive sequence.

Satellite DNA – repetitive DNA clustered in discrete areas. Also known as ‘junk DNA’

It is thought dispersed DNA has no specific coding function, but can move from one location to another (transposable elements). Importance not yet understood.

Who is Barbara McClintock?

Homologous chromosomes

Defined as: Two chromosomes

carrying the same sequence of genes.

Not identical because although the genes are the same, the

alleles are different.

Guess the genome…

E. Coli

5 million base pairs

Paris Japonica

150,000

million base pairs

T2 phage (virus)

0.18 million base pairs

Drosophila melangaster

140 million base pairs

Homo sapiens

3000 million base pairs

A - ancestral EutherianB - ChickenC - Short-tailed opossumD - AardvarkE - MinkF - Red foxG - Ancestral SciuridaeH - MouseI - Human

Locus of a gene

• The position of a gene on a chromosome

Haploid V’s Diploid

Haploid nuclei Diploid nuclei• 23 chromosomes

(humans)• Gametes (sex

cells)• Single copy of

each gene

• 23 chromosome pairs

• Haploids fuse to form zygote

• Two copies of each gene

Reproduction by fusing haploid cells leads to much greater variation, reduced chance of inheriting recessive mutations & increased

hybrid vigour (stronger offspring – sometimes!).

Who has the most chromosomes?

78 24

Who has the most chromosomes?

46 48

Sex chromosomes

Female: XXMale: XY

X X

X XX XX

Y XY XY

50% F50% M

Every time!

Karyotyping & karyograms

Downs syndrome

1.Definition?2.Causes?3.Diagnosis?4.Risk factors?5.Prevalence?6.Treatment?

Observing mitosis in garlic root tip

• http://www.nuffieldfoundation.org/practical-biology/investigating-mitosis-allium-root-tip-squash