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/supercoiled. 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. (545% 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 Eutherian B - Chicken C - Short-tailed opossum D - Aardvark E - Mink F - Red fox G - Ancestral Sciuridae H - Mouse I - Human Locus of a gene • The position of a gene on a chromosome Haploid V’s Diploid Haploid nuclei • 23 chromosomes (humans) • Gametes (sex cells) • Single copy of each gene Diploid nuclei • 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 X X X XX XX Y XY XY Female: XX Male: XY 50% F 50% 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/practicalbiology/investigating-mitosis-allium-root-tip-squash