Biological Diversity Topic 3 ppt.pptx

TOPIC 3 DNA IS THE INHERITED MATERIAL RESPONSIBLE FOR VARIATION DNA – TRANSMITTER OF GENETIC CODE • https://vimeo.com/60747882 • Cells of all living things contain a “blueprint” molecule that acts as a set of instructions that is passed on to its offspring • The molecule is called DNA – deoxyribon...

TOPIC 3 DNA IS THE INHERITED MATERIAL RESPONSIBLE FOR VARIATION DNA – TRANSMITTER OF GENETIC CODE • https://vimeo.com/60747882 • Cells of all living things contain a “blueprint” molecule that acts as a set of instructions that is passed on to its offspring • The molecule is called DNA – deoxyribonucleic acid • DNA is contained in the nucleus of each cell • DNA was first identified in 1869, and analysis of cells from many different organisms led scientists to determine that DNA existed in ALL of them. • In 1953, James Watson and Francis Crick unraveled the structure of the DNA molecule, revealing the same chemical building blocks across all living things. DNA’S STRUCTURE • The DNA molecule is like a ladder that has been twisted into a continuous spiral. This is called a double helix. • Sides of the ladder : alternating sugar and phosphate subunits. • Rungs of the ladder: pairs of nitrogen bases (four types) : • ADENINE (A) and THYMINE (T), GUANINE (G) and CYTOSINE (C) • The genetic code is determined by the arrangement of just these four PAPER DNA MODEL LAB • Complete the paper DNA model activity and answer the accompanying lab questions • Lessons Learned: ✓ I can identify the components of a DNA molecule ✓ I can identify the four bases in the DNA double-helix and explain which bases pair together ✓ I can predict what the second half of a DNA strand would look like if I was given one side of the double-helix as a template ✓ I can identify the following parts of a DNA double helix: ✓ Adenine, Cytosine, Guanine, Thymine ✓ Deoxyribose, Phosphate, Nitrogen base ✓ Sugar phosphate backbone, Double-helix GENES Recall: • A discrete trait can be one of two forms (e.g. tongue rolling) • It is encoded by two alleles of one gene • A continuous trait can come in a range of forms (e.g. height) • It is encoded by the combination of alleles of many genes What are genes and alleles? Gene: • a segment of DNA that encodes the instructions to express a heritable trait • exists as a pair of alleles (two forms of the same gene) ALLELES Alleles: • An organism inherits one allele from its mother and one allele from its father. • They can be either a dominant form or recessive form • An organism is a purebred or homozygous if both alleles are the same. • 2 dominant alleles or 2 recessive alleles • An organism is a hybrid or heterozygous if both alleles are different. • one dominant allele and one recessive allele GENOTYPES VS PHENOTYPES Genotype: • • • • Describes the pair of alleles an organism has Use a capital letter for a dominant allele Use a lower case letter for a recessive allele E.g. can roll tongue (use TT) can’t roll tongue (use tt) Phenotype: • Describes the trait that is expressed • E.g. can roll tongue or can’t roll tongue Dominant and Recessive Genes 2 min Genetics with Model Organisms • Extra information: • • • • • • Diploid: A full set of DNA Haploid: Half a full set of DNA Protein: Made of amino acids Alleles: A version of a gene Phenotype: What the trait looks like Genotype: What alleles the genes are made of (Bb) or (aa) Mendel’s Punnett Squares 3 min CAT COAT COLOUR Consider cat coat color as a discrete trait with 2 forms: black and white • The dominant allele encodes black coat, the recessive allele encodes white coat • B = dominant allele • b= recessive allele • Purebred black cat: • Genotype = BB or “homozygous dominant” • Phenotype = black coat • Purebred white cat: • Genotype = bb or “homozygous recessive” • Phenotype = white coat • Hybrid cat: • Genotype = Bb or “heterozygous” • Phenotype = black coat • If a breeder wishes to produce black cats: • Only purebred black cats whose ancestors have produced only black offspring for several generations should be used ➢ BB = homozygous dominant, black • If a breeder wishes to produce white cats: • Only purebred white cats should be used ➢ bb = homozygous recessive, white Dominant Traits • Suppose a purebred white cat and a purebred black cat. What pattern of inheritance will be observed in the hybrid offspring? Cross between purebred white female cat and purebred black male cat. • In our example, every kitten in the resulting litter has a black coat. WHY? • Black coat colour in cats is an example of a dominant trait • A Punnett Square can be used to predict the probability of inheritance as a ratio and/or percentage B B b Bb Bb b Bb Bb • The hybrid kittens have inherited the black coat colour allele from the father and the white coat color allele from the mother • The DNA instructions encoded by the black-coat allele completely mask the DNA instructions encoded by the whitecoat allele • All the offspring are Bb = heterozygous = hybrid black RECESSIVE TRAITS • Suppose we cross two hybrid black offspring. **Hybrid genotypes are carriers of the recessive trait ​ B​ b B BB​ Bb​ b​ Bb​ bb​ • 3 out of 4 or 75% probability the kittens will have black coats • 1 out of 4 or 25% probability the kittens will have white coats Describe the genotypes found in the Punnett square • BB – Homozygous dominant • Bb – Heterozygous • bb – Homozygous recessive Punnett Squares These are used to predict the probability of inheritance How to create Punnett squares • • Draw a square divided into four parts • • Look at the letter to its left, and the letter above it Write both these letters in the empty box • Repeat for the remaining three boxes Add parents' genotype to either side PATTERNS OF INHERITANCE Complete Dominance: • Expression of the dominant allele completely masks the expression of the recessive allele Incomplete Dominance: • Neither allele is dominant, and it results in a blending of the two forms • Ex. skin color, height, hand size, and vocal pitch Co-Dominance: • Both alleles are equally expressed and both forms of the trait are distinguishable from one another • Ex. Spotted coloured animals, sickle cell anemia CONTINUOUS TRAITS • Think about dogs. All dogs belong to the same species and all have a hairy coat – this is an INHERITED CHARACTERISTIC. • But when we observe dogs, we see many different versions of “hairy coat”. The hair may be straight or curly, short or long, coarse or fine, as well as many possible colors. A number of gene pairs and different allele combinations are responsible for these characteristics! Offspring Unlike Either Parent: • We now know that most patterns of inheritance are not as simple as we thought • It is too complex to be explained solely by the dominant-recessive pattern or even by incomplete dominance • Many gene locations and several possible alleles may be involved Environmental Factors: • The traits that are expressed in organisms are also greatly influenced by the environment (for example, trauma, nutrition, exposure to toxins). DNA ARRANGEMENT • Think of it like this: -a gene is like a sentence -a chromosome is like a chapter -DNA is like a book! • How long is your DNA? Alleles & Genes 8 min What is PTC found in? Also known as phenylthiourea, the chemical structure of PTC resembles toxic alkaloids found in some poisonous plants. Although PTC is not found in nature, the ability to taste it correlates strongly with the ability to taste other bitter substances that do occur naturally, many of which are toxins. CHROMOSOMES • DNA contains all the instructions for an organism’s characteristics • A gene is a segment of DNA that contains coded instructions for a specific trait • DNA is an extremely long molecule and contains many genes • Usually, DNA exists as a loose strands (known as chromatin) in the nucleus of a cell (like a bowl of spaghetti) • When a cell divides, DNA is arranged into compartments called chromosomes • This keeps DNA very organized so that it is properly passed down to its offspring • Every cell in an organism’s body (except for gametes) must have a complete set of chromosomes in order to properly function • Chromosome number varies from one species to another…. • In humans, a complete set is 46; however, this number differs across all organisms. Dogs have 78! • Chromosomes are almost always organized in pairs. This means that human cells contain 23 pairs, for a total of 46. • Remember, a gene exists as a pair of alleles • For each gene, one allele is on one chromosome, the other allele on the other chromosome • When we inherit one chromosome from our mother, we inherit one allele, when we inherit one chromosome from our father, we inherit one allele • As a result, we get a pair of alleles for that gene (recall Punnett Squares!) CELL DIVISION • Review….Asexual reproduction is the production of offspring genetically identical to the parent. • Sexual reproduction is the production of offspring that are genetically different from their parents. • When a paramecium (a single-celled organism) undergoes binary fission, it must DOUBLE its DNA before splitting to ensure that the two new offspring cells each receive a full set of DNA. Amoeba Sisters Mitosi Mitosis: s Video (8 min) • cellular division of somatic (body) cells of multicellular organisms • produces two new cells from one cell • the two new cells have the same number of chromosomes as the original cell • responsible for the growth and cellular repair of a multicellular organism Meiosis: Amoeba Sisters Meiosis Video (7.5 min) • a special kind of cellular division in sexually reproducing organisms • involves two cellular divisions resulting in the formation of gametes (sex cells) • During sexual reproduction, male and female gametes unite to form a zygote, which develops into a new organism. • Gametes contain half the number of chromosomes compared to somatic cells, so that the zygote ends up with a full set of chromosomes. Mitosis: Begins with 1 cell containing a full set of chromosomes -chromosomes double -cell splits, producing 2 cells containing a full set each Meiosis: Begins with 1 cell containing a full set of chromosomes -chromosomes double -cell splits, producing 2 cells containing a full set each - 2 cell split AGAIN, producing 4 cells containing HALF Mitosis: Mitosis Rap Song  2 min Questions to Think About • What do we use mitosis for in our bodies? • What do we use meiosis for in our bodies? • What happens if mitosis doesn’t happen properly? • What happens if meiosis doesn’t happen properly? HeLa Cells – Cells that can’t control how often they divide Salamander Develops from Zygote 6.5 min