Genetics and Evolution Revision Session PDF

Genetics and Evolution Final Revision Session Intended Learning Outcomes On successful completion, you will be able to: Explain the structure of genetic material and the cellular mechanism of heredity Analyse patterns of inheritance Discuss the theory and mechanisms of evolution Exp...

Genetics and Evolution Final Revision Session Intended Learning Outcomes On successful completion, you will be able to: Explain the structure of genetic material and the cellular mechanism of heredity Analyse patterns of inheritance Discuss the theory and mechanisms of evolution Explain how inherited and learnt traits can evolve at the population level  Assessment methods Assignment 1 Written Exam (50%) Genetics on 17.12.24 Intended Learning Outcomes- on successful completion you will be able to: 1.Explain the structure of genetic material and the cellular mechanism of heredity 2.Analyse patterns of inheritance One hour written exam. Section A Short-answer and multi-choice questions 60% Section B Inheritance patterns – problem solving using Punnett Squares 40%  Assessment methods Assignment 2 Evolution Case Study (50%) Assignment 2 – Evolution Booklet (1500 words) (50%) Intended Learning Outcomes - on successful completion, you will be able to: 3. Discuss the theory and mechanisms of evolution 4. Explain how inherited and learnt traits can evolve at the population level.  What is Genetics? Genetics = study of genes and the chromosomes that house them Genetics = science of Heredity - the process that brings about the similarities between parents and their offspring Genes are - units of heredity which are transferred from parent to offspring, helps to determine some traits of the offspring. Humans have about 20,000+ genes (genome)  DNA DNA (deoxyribose nucleic acid) = genetic material that an individual inherits from their parents. Present in the nucleus of all cells packed tightly in the nucleus cells as chromosomes. Controls all the chemical changes which take place in cells E.g. the kind of cell which is formed, (muscle, blood, nerve etc) is controlled by DNA The type of organism which is produced (buttercup, giraffe, herring, human etc.) is controlled by DNA DNA molecule 3 DNA very large molecule made up of a long chain of sub-units The sub-units = nucleotides Each nucleotide is made up of: B - a sugar = deoxyribose A - a phosphate group -PO4 C -an organic base (A,C,T,G)  Nucleotides Ribose is a sugar, like glucose, but with five carbon atoms in its molecule (mRNA) Deoxyribose is almost the same but lacks one oxygen atom (DNA) The paired strands are coiled into a spiral called bases THE DOUBLE HELIX sugar-phosphate chain  Replication Before a cell divides, the DNA strands unwind and separates Each strand makes a new partner by adding the appropriate nucleotides The result is that there are now two double-stranded DNA molecules in the nucleus So each nucleus contains identical DNA This process is called replication The sequence of bases in DNA forms the Genetic Code A group of three bases (a codon) controls the production of a particular amino acid in the cytoplasm of the cell (protein synthesis) The different amino acids and the order in which they are joined up determines the sort of protein being produced! Triplet code This is known as the triplet code Each triplet codes for a specific amino acid The amino acids are joined together in the correct sequence to make part of a protein Ala Val Gly Gly Arg Pro Leu Gly ESSENTIAL Amino Acids Chromosomes - Structure Before cell division there is an increase in the condensation of the chromosomes to make them visible. Proteins (histones) are involved in this condensing attach themselves to the DNA molecule and produce chromatin Chromatin consists of the unravelled condensed structure of DNA for the purpose of packaging into the nucleus  Chromosomes The replicated copies of the chromosome are called sister chromatids They join at the centromere The short ‘arms’ of chromosomes are called ‘p’ arms while the longer ones are called ‘q’ arms. Chromosomes and genes A a Because the chromosomes are in B b pairs, the genes they carry are also in pairs C c D d Each member of a pair of genes comes E e from either the male or the female parent just as the chromosomes do F f G g The individual genes of a pair, control the same characteristic, e.g. B and b H h could control eye colour; G and g could control hair colour I I  Re-cap! Cell Replication Mitosis – happens in all parts of the body throughout the animal’s life, to allow growth and to repair damaged cells. Meiosis – happens only in the sperm and egg cells.  Mitosis – Key Points Mitosis (mitotic division) Results in two identical cells Each cell produced contains the same genetic information – no changes have occurred The number of chromosomes (2n) remain the same in the new cells produced No genetic variation occurs during mitosis (I Prefer Milk And Tea) Cell division  Meiosis - Key points Occurs in the gametes (sex cells- sperm & ovum) Has 2 divisions (stage 1 and stage 2) A single cell divides twice to produce four cells containing half the original amount of genetic information. 4 daughter cells haploid (n) gametes that are genetically unique from each other and the original parent (germ) cell. Males = four cells are all sperm cells Females - one of the cells is an egg cell while the other three are polar bodies (small cells that do not develop into eggs).  Mendel was the first biologist to use mathematics – to explain his results quantitatively. Mendel predicted: 1. The concept of genes 2. That genes occur in pairs 3. That one gene of each pair is present in the gametes He came up with 3 laws of genetics   Dihybrid cross F2 If F1 generation is allowed to self pollinate, Mendel observed 4 phenotypes: Possible gametes: Tt Pp  Tt Pp TP Tp tP tp (tall, purple) (tall, purple) TP Tp tP tp Four TTPP TTPp TtPP TtPp phenotypes TP TTPp TTpp TtPp Ttpp observed Tp Tall, purple (9); TtPP TtPp ttPP ttPp tP Tall, white (3); TtPp Ttpp ttPp ttpp tp Short, purple (3); Short white (1)  Why does this work? If one of the genes is physically very close to the other on the same chromosome – the dihybrid cross DOES NOT work In this situation they are more likely to be passed on together i.e. they are LINKED… The chances of them being separated during crossing over is small  Incomplete (partial) Dominance Cross a red snapdragon (RR) with a white snapdragon (rr) = PINK flowers (Rr)! Genes show incomplete dominance when the heterozygous (Rr) phenotype is a form of gene interaction RR  rr in which both alleles of a gene at a locus are partially expressed. The pink phenotype is a mixture of Rr both alleles being expressed at the same time in every cell  Co-dominance In co-dominance, BOTH alleles contribute to the phenotype. They are both independently and equally expressed This gives the appearance of a mixture of the traits Eg Roan coat colour in horses and cocker spaniels  Sex Chromosomes: XX female and XY male. The Y chromosome is smaller than the X, the traits on this portion of the Y chromosome are transmitted only from fathers to sons X Inactivation in Female Mammals In mammalian females, one of the two X chromosomes in each cell is randomly inactivated during embryonic development (Barr body) Example – female calico cats  Sex linked Punnett squares In cats, the gene for calico cats is codominant. Females that receive a B and an R gene have black and orange splotches on white coats. Males can only be black or orange, but not calico A calico female’s genotype would be XB XR Example - cross of a female calico cat with a black male XB Y X B XB = Female Black XB XB XB X B Y XB Y = Male Black X R X B = Female XR XR X B X R Y calico X R Y = Male orange 25% of the kittens will be black and male 25% of the kittens will be orange and male 25% of the kittens will be calico and female 25% of the kittens will be black and female  Polygenic Traits Many traits are controlled by two or more genes - polygenic traits. One polygenic trait can have many possible genotypes and phenotypes e.g. Growth rate in animals is a polygenic trait because it is affected by many genes but with no gene having an occurring influence Greatly influenced by environment e.g. Lack of feed, Heat/ cold, stress etc.  Epistasis The interaction between different genes, when a genotype at one locus may influence the effect of a second genotype – preventing it from being expressed (hypostatic) due to mutation It is similar to dominance but involves different genes e.g. coat colour albinism. The albino epistatic gene masks the hypostatic gene for coat colour DNA transcription DNA translation TRANSCRIPTION Translation  Types of mutations 1). Germline mutations occur in gametes = any inherited disease passed to offspring 2). Somatic mutations occur in non-reproductive cells and so won’t be passed on to offspring. 3). Chromosome mutations are mutations that change chromosome structure = change in geno and phenotype 4). Point mutations (Substitution) change a single nucleotide (a change in one base in the DNA sequence) 5). Frameshift mutations (insertion) or (deletion) involving a number of base pairs that is not a multiple of three  Genetic engineering There are several ways in which genes from one organism can be inserted into a different organism 1. They can be coated on to microscopic gold particles and ‘fired’ into the cells 2. They can be delivered by viruses 3. They can be transmitted by using plasmids, present in bacteria 4. Use restriction enzyme (protein isolated from bacteria) that cleaves DNA sequences at sequence-specific sites, producing DNA fragments with a known sequence at each end. 5. The use of restriction enzymes is critical to certain laboratory methods, including recombinant DNA technology and genetic engineering  18 Cloning Natural cloning – asexual reproduction (Bacteria, plants, fungi, some invertebrates), all the offspring receive a full set of genes from the parent (they are identical to each other and to the parent) Vertebrates do not reproduce asexually but clones can be produced artificially.. Done by transferring the nucleus from a body cell to an egg cell (ovum) from which the nucleus has been removed  28 Stem Cells Skin stem cells can normally give rise only to skin epidermal cells Bone marrow stem cells can normally give rise only to 6 types of blood cell But embryonic stem cells can produce all the cells of the body Human embryonic stem cells can be obtained from 10 day embryos* These embryonic stem cells can be cultured in a special nutrient solution It may become possible to treat stem cells from specialised tissues with hormones and growth factors that cause them to produce a wider range of specialised cells* Examples - skin stem cells producing nerve cells; bone marrow cells producing skin, bone, muscle and fat.  Any Questions? Exam start time 1pm – 2.15pm