Genetics and DNA

1. Genetics and DNA

2. Contents • Genes • Alleles • Clones • Tissue Culture • Animal Cloning • Evolution • Mutation • Evidence for Evolution • Layout of Fossils • Example of Evolution • Extinction • Variation

3. Genes • Inside the nucleus  chromosomes • Chromosome = 1000s of coils of genes • Gene = comprise ‘DNA’ that decides our characteristics • DNA = deoxyribose nucleic acid (chemical) • Each gene acts as a code for a particular characteristic

4. Genes • A human egg cell and sperm cell contains 23 chromosomes • Embryo therefore contains 23 pairs of chromosomes • Each pair contains a gene from your mother, and a gene from your father for a particular characteristic • So each pair contains two “options” for a characteristic • These options are called alleles • e.g. gene = eye colour; alleles = blue eye colour, brown eye colour

5. Alleles • An Allele is an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome. • Alleles are dominant or recessive • Homozygous = two same alleles (purebred) • Heterozygous = two different alleles • Dominant + recessive  dominant • Dominant + dominant  dominant • Recessive + dominant  dominant • Recessive + recessive  recessive e.g. BB, Bb = brown eyes; bb = blue eyes Two parents are Bb + bb; offspring has 50% chance of blue eyes

6. Eye Colour A heterozygous brown-eyed father and a blue-eyed mother: 50:50 chance of being either brown eyed or blue eyed

7. Clones • Clone = organism that is genetically identical to its parent • Cloning in nature: • Potato tubers • Strawberry runners • Daffodils • Tissue Cultures: • Plants multiply very quickly by human intervention • A number of cells are taken from the ‘parent’ plant and are grown by mitosis in growth hormones

8. Tissue Culture

9. Animal Cloning • Simple organisms reproduce by mitosis (e.g. amoeba) so identical offspring are produced • Artificial Clone Example: Dolly the Sheep (1996) • Adult sheep egg removed from ovary – nucleus removed • Empty egg cell fused with DNA of udder cell of donor sheep • Fused cell developed, using donated DNA • Embryo implanted into uterus of foster-mother sheep Result: Dolly became genetically identical to donor sheep

10. Evolution • Darwin made 4 key observations: 1) Living things tend to produce more offspring than survive 2) Population numbers in a species stay constant over time 3) Each species displays a wide variation in features 4) Some of these variations are passed on to offspring • Living things are in continuous competition with each other for food, space, mates… • ‘Survival of the Fittest’! • Natural Selection: Survival of organisms best suited to surviving and reproducing in their environment

11. Mutation • During replication, an organism’s genetic make-up (DNA) can change or mutate. • If mutation is large… - organism will probably not survive to reproduce • If mutation is small… - change might be beneficial. Offspring will flourish, doing better than others in that species. - Many more offspring will inherit this beneficial mutation and will be better suited to that environment… • Thus continues natural selection…

12. Evidence for Evolution • Comes from rocks and fossils… • The remains of organisms from millions of years ago are preserved as fossils in sedimentary rocks • Fossils are formed in one of two ways: 1) Organism decomposes, and minerals become implanted in the tissue so that the organism turns to rock 2) Organism’s shape leaves an impression in the ground • Fossils are formed in areas of insufficient oxygen to decay, in low temperatures (glaciers) and high soil acidity (peat bog)

13. Example of Evolution • The horse • Fossils provide evidence for the main stages of evolution of the horse over 60 million years • Dog-sized  2m in height • Multi-toed feet for walking on forest floor  single-toed hooves for running over open country

14. Extinction • Species or whole families of organisms die out • Any of 3 factors can contribute to extinction: - environment changes too quickly - new predator or disease kills them - beaten by another species for competition for food • The environment is slowly changing. Gradually, certain characteristics will become favourable and those species without these characteristics will die out • The environment can change quickly. This affects great numbers of species that cannot keep up with the changes required for survival

15. Environmental Variation • Causes: climate, diet, lifestyle, culture, accidents • Environment affects how our inherited characteristics develop • Twins who grow up separately might become very different: • e.g. fashion, taste, hair colour, build, personality, aptitudes

16. Genetic Variation • Causes: - Mixing of parent information during meiosis - Gamete forms from a unique combination of genetic information • Siblings can have both similar and very different traits • They are mixtures of their parents, each sibling can receive different characteristics of their parents • e.g. natural hair colour, eye colour, blood type

17. Continuous vs. Discontinuous • Continuous Variation - Small differences between individuals - Greatly affected by environment - e.g. height, shoe size, length of hair - plotted on a line graph • Discontinuous Variation - Differences that are classed or categorised - Not greatly affected by environment - e.g. blood group, sex, hair colour, eye colour - plotted on a bar chart or pie chart

18. Summary • Genes: instructions for our genetic make-up (e.g. eye colour) • Alleles: different types of the same gene (e.g. blue eyes) • Clones: genetically identical to the parent (mitosis) • Tissue Culture: Many of a specialist organism type produced • Animal Cloning: used for selective breeding • Evolution: Survival of the fittest! • Mutation: Cells mutate under certain conditions • Evidence for Evolution: Rocks and fossils • Layout of Fossils • Example of Evolution: Horse • Extinction: Occurs for 3 main reasons