Lecture 10 Do chromosomes transmit hereditary instructions Hybridization crossing of two true breeding varieties 3 1 purple white purple dominant white recessive Some basic flower biology Flowers contain pollen producing anthers and egg producing ovary stigma on top For pea plants fertilized eggs develop into seeds in pods Seeds or peas escape from pod and may grow into new plant Mendel s Theory of Inheritance 1 Particles genes guide development of characteristics 2 Genes pass unchanged from parents to offspring in sperm and egg 3 All body cells have pair of genes for each characteristic 4 During gamete production paired genes separate equal chance gamete will receive one or other gene 5 Paired genes pass independently not linked 6 Genes recombine randomly during fertilization 7 One gene of the pair dominates and guides development of observable characteristic Punnett square useful way for predicting the allele composition of offspring from a cross between individuals of known genetic makeup Genotype vs Phenotype Ratios Genotype an organism s genetic makeup Phenotype an organism s appearance it s traits The ratios can be the same or different Chromosome Theory of Inheritance Walther Flemming and others 1 Chromosomes contain hereditary instructions 2 Transmission to new body cells occurs due to cell division and mitosis full set of chromosomes 3 Sperm and egg produced by meiosis half the set of chromosomes 4 Transmission to offspring when sperm enters egg to produce zygote full set of chromosomes Walter Sutton 1903 proposed that genes which he could not see are in chromosomes which he could see If chromosomes contain genes then chromosomes and genes should behave same way 1 gametes contain half the chromosomes as body cells Mendel half number of genes 2 chromosome pairs separate during gamete production Mendel gene pairs separate 3 fertilized egg contains twice number of chromosomes as each gamete Mendel egg twice number of genes 4 chromosomes don t change from generation to next Mendel genes don t change Crossing Over Homologous chromosomes exchange parts Results in four gametes that have genetically unique chromosomes Aids in independent assortment Lecture 11 How do embryos develop Mendel s theory Random segregation of chromosomes Independent assortment Only when genes are on different chromosomes Dominant inheritance Discontinuous or discrete characteristics either or Other inheritance patterns Incomplete dominance None of the alleles are dominant What would happen in an F3 generation crossing one pink and one white flower RW x WW 2 RW 2WW ectoderm mesoderm 2 pink and 2 white Continuous characteristics height skin color quickness Skin color polygenic inheritance Why is sex important Gene mixing during sexual reproduction produces greater genotypic and phenotypic diversity hence reduces risk of extinction During meiosis crossing over of chromosome segments During meiosis when paired chromosomes line up not all male or female on same side During fertilization random recombination Crossing Over Homologous chromosomes exchange parts Results in four gametes that have genetically unique chromosomes Aids in independent assortment Where Do Cells Move 1 Egg cells divide to produce hollow ball of cells blastula 2 Surface cells move inward producing a slit Upper part is dorsal lip 3 Dorsal lip forms a ring and becomes anus 4 Inside cavity becomes gut gastrula 5 Cell layers form in the gastrula inner layer endoderm external layer middle layer What Might Cause Cells to Differentiate All cells from one cell the zygote presumably with two sets of chromosomes genes instructions Generate at least two possible explanations for differentiation Cell Differentiation Theory 1 Genes guide development 2 Genes initiate changes in fertilized egg to produce differentiated cytoplasm 3 Degree of cytoplasmic differentiation varies from species to species 4 As cell division occurs identical genes pass to each offspring cell 5 Each division splits cytoplasm into two regions each with differentiated cytoplasm 6 Differentiated cytoplasm modifies genes 7 Modified genes produce different cell types Lecture 12 What are genes made of Cells contain at least three groups of molecules proteins lipids and carbohydrates Friedrich Miescher detected oxygen carbon hydrogen nitrogen and phosphorus atoms This molecule was acidic and was present in the nucleus thus it was called nucleic acid Composed of three smaller molecules 1 a five carbon sugar deoxyribose 2 a phosphorus with four oxygen atoms phosphate 3 one or two ring structures composed of nitrogen and carbon nitrogenous bases New name Deoxyribonucleic acid DNA Four nitrogenous bases genetic alphabet adenine thymine cytosine guanine Nucleotide Phosphate group Sugar Nitrogenous base Watson Crick s theory of DNA structure and replication 1 DNA consists of a two strand spiral helix composed of alternating deoxyribose and phosphate parts 2 The strands are connected in A T and G C pairs linked to the deoxyribose parts 3 The pairs may be in any sequence 4 When DNA replicates the pairs separate permitting the strands to separate coil unwinds 5 New nucleotides will bond to the exposed A T G C in each strand 6 A new strand is formed when deoxyriboses attach to phosphates and coils with the original strand 7 Two new DNA molecules are produced Lecture 13 How do genes work Basic concepts Proteins are composed of long chains of amino acids and the chains fold in different ways into huge molecules Many proteins are enzymes which are catalysts in metabolic reactions How does DNA code for enzyme synthesis Most proteins consist of no more than twenty amino acids Thus we need to understand how DNA codes for sequences of amino acids Protein synthesis happens in the cytoplasm How do the instructions leave the nucleus DNA transcription Crick suggested that single strand molecules are synthesized inside the nucleus and transported out to the cytoplasma It appears that this molecule contains a different sugar than DNA ribose instead of ribonucleic acid RNA deoxyribose SINGLE STRANDED The nitrogenous bases in RNA are similar to those in DNA except that Thymine T is replaced by Uracil U A DNA sequence ATTCGC will therefore be transcribed into UAAGCG in mRNA A DNA sequence ATTCGC will therefore be transcribed into UAAGCG in mRNA What would be the corresponding RNA sequence to the following DNA sequence TTGATAGC DNA Question AACUAUCG RNA Answer DNA transcription RNA translation When a new