Genetics and DNA

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

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

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

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. 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 Alleles are dominant or recessive Homozygous = two same alleles (purebred) Homozygous = two same alleles (purebred) Heterozygous = two different alleles Heterozygous = two different alleles Dominant + recessive  dominant Dominant + recessive  dominant Dominant + dominant  dominant Dominant + dominant  dominant Recessive + dominant  dominant Recessive + dominant  dominant Recessive + recessive  recessive Recessive + recessive  recessive e.g. BB, Bb = brown eyes; bb = blue eyes Two parents are Bb + bb; offspring has 50% chance of blue eyes

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

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

Tissue Culture AdvantagesDisadvantages Many plants grow in a short amount of time Same genetic make-up: vulnerable to disease Little space is needed, conditions are controlled No new characteristics can arise by chance All new plants inherit the desired characteristics No variation: danger of reducing gene pool

Animal Cloning Simple organisms reproduce by mitosis (e.g. amoeba) so identical offspring are produced Simple organisms reproduce by mitosis (e.g. amoeba) so identical offspring are produced Artificial Clone Example: Dolly the Sheep (1996) Artificial Clone Example: Dolly the Sheep (1996) 1) Adult sheep egg removed from ovary – nucleus removed 2) Empty egg cell fused with DNA of udder cell of donor sheep 3) Fused cell developed, using donated DNA 4) Embryo implanted into uterus of foster-mother sheep Result: Dolly became genetically identical to donor sheep

Evolution Darwin made 4 key observations: 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 Living things are in continuous competition with each other for food, space, mates… ‘Survival of the Fittest’! ‘Survival of the Fittest’! Natural Selection: Survival of organisms best suited to surviving and reproducing in their environment Natural Selection: Survival of organisms best suited to surviving and reproducing in their environment

Mutation During replication, an organism’s genetic make-up (DNA) can change or mutate. During replication, an organism’s genetic make-up (DNA) can change or mutate. If mutation is large… If mutation is large… - organism will probably not survive to reproduce If mutation is small… 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… Thus continues natural selection…

Evidence for Evolution Comes from rocks and fossils… Comes from rocks and fossils… The remains of organisms from millions of years ago are preserved as fossils in sedimentary rocks The remains of organisms from millions of years ago are preserved as fossils in sedimentary rocks Fossils are formed in one of two ways: 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) Fossils are formed in areas of insufficient oxygen to decay, in low temperatures (glaciers) and high soil acidity (peat bog)

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

Extinction Species or whole families of organisms die out Species or whole families of organisms die out Any of 3 factors can contribute to extinction: 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 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 The environment can change quickly. This affects great numbers of species that cannot keep up with the changes required for survival

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

Genetic Variation Causes: 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 Siblings can have both similar and very different traits They are mixtures of their parents, each sibling can receive different characteristics of their parents They are mixtures of their parents, each sibling can receive different characteristics of their parents e.g. natural hair colour, eye colour, blood type e.g. natural hair colour, eye colour, blood type

Continuous vs. Discontinuous Continuous Variation 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 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

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