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DNA and Inheritance Hayley Siddons DNA • What is DNA – Deoxyribonucleic Acid – The unit of inheritance for all living organisms • DNA is packaged into Chromosomes in the cell – To make it more compact to fit into the cell – Easy of replication and equal division of the DNA during cell division (reproduction) Chromosomes in cells • Same species of organisms always have the same amount of chromosomes – Humans have 46 – Fruit Fly have 8 – Corn has 20 Human (female) Karyotype • Chromosomes which are not the sex chromosomes are called Autosomes Chromosomes in cells The X shape of the chromosome is because during cell division (only time you can see defined Chromosomes down a microscope) each chromosome is duplicated and the pairs are joined in the middle at the centromere Mitosis Video https://www.youtube.com/watch?v=L0kenzoeOM Mitosis • Cell duplication • 1 parent cell into to 2 identical daughter cells • Stages of Mitosis • Interphase – Prophase – Metaphase – Anaphase – Telophase • cytokinesis • Cell in normal functioning mode. • Signal is given to enter into Mitosis and the cell replicates its DNA • DNA condenses down into the X shape that we recognise as a chromosome • Nuclear membrane breaks down • Chromosomes line up in the middle of the cell (equator) • The X shape of the chromosomes gets pulled apart • One of the identical chromatids goes to one side (pole) of the cell • The other identical chromatid goes to the other side (pole) of the cell • Chromosomes are now on each side of the cell • Nuclear membranes start to form around each of the DNA/chromosome groups • Cells start forming cell membranes between the groups of DNA (looked pinched) • Cell membranes ‘pinch off’ in between the two nuclei • Forming 2 genetically identical daughter cells Worksheet Activity Making sex cells • Sex cells (sperm and eggs) have (and need to have) half the amount of chromosomes as the nuclei of all other cells • This is because when the sperm and egg cells combine during fertilisation the resulting cells (offspring) have the required amount of chromosomes and no more Pg 59 Activity Pg 59 Meiosis Video https://www.youtube.com/watch?v=qCLmR9YY7o&spfreload=10 • Meiosis 1 – Separation of the ‘X’ shaped chromosome pairs (one from mum, one from dad) – Results in half the amount of genetic material (eg now 23 pairs) – Chromosomes get randomly separated, so will get a mixture of mum and dad chromosomes going into the 2 cells • Meiosis 2 – Separation of the sister chromatids • 1 cell going through meiosis results in 4 cells, all with half the amount of genetic material Mitosis vs Meiosis Worksheet Determining Sex of the offspring • In humans only 2 chromosomes of the 46 chromosomes contribute to determining the sex (gender) of the offspring – The other 22 pairs of chromosomes have no effect Sex Determination Activity Pg 61 Check Questions Pg 62 Extracting DNA Practical DNA • Deoxyribonucleic Acid • DNA made up of – Sugar Phosphate Backbone – Nitrogen-containing substances called bases • • • • Adenine (A) Guanine (G) Thymine (T) Cytosine (C) • The 2 stands of DNA bind together through the bases – forming base pairs – A with T – G with C • This holds the DNA molecules in the well known double helix structure DNA Strands Write the complementary strand A T G T A C G G T A C G G A Write the complementary strand T T G C T G C C A T A A G A Genes • Organisms are different because the proteins in their cells are different • The DNA provided the information about which amino acids make up proteins • It is the arrangement of the base pairs (A-T, C-G) which will determine the type of protein made • Sections of DNA which ‘code’ for a protein are called Genes • Determines the organisms characteristics The DNA Code • If the two strands in the DNA molecule of DNA separated, part of the strand would look like this: It is the sequence of the DNA bases which form the code • Any three of these bases form a triplet code for an amino acid. – Eg GAT codes for Aspartic Acid – TCG codes for Serine The DNA Code • With the 4 bases – 4x4x4 = 64 triplets which can be coded • This is more than the 20 amino acids used by cells to make proteins • Many amino acids have more than one coding triplet The DNA Code • Different sequences code for different amino acids, which make up different proteins • the number of amino acids in a protein can be less than a dozen and more than 50 000. • Therefore a DNA molecule can code for thousands of different proteins Pg 66 Animals which are classes as Albino are born without any skin or hair colouring This is because the gene in each cell does not produce any colour pigments Because there has been a detrimental alternation in the original gene which codes for colour pigmentation Mutations • Are Alterations in genes or important parts of the DNA molecule • Depending on where the mutation is and how it effects the gene/gene products/proteins it can be bad/fatal for the organism or it can be good for the organism Mutations • Can be either a single base change in the DNA • Or a whole deletion or insertion of a segment of DNA into the gene • Or a rearrangement of the DNA segments on chromosomes AAT CAA CCT TCA Asparagine glutamine proline serine AAT CCA CCT TCA Asparagine proline proline serine Depending on the base change in a DNA sequence, you could just change one amino acid or you could change it into a stop codon and thus shorten the protein. Either one could have a drastic effect depending on where it is located in the protein How do Mutations occur • Occur naturally through normal DNA replication processes – 1 mutation in every 30 million bases – Very slow rate of mutation • Mutation rates can be increased by exposure to – High energy radiation • Nuclear radiation • X-rays – Chemicals – UV in sunlight Pg 68 Genomes A genome is an organism's complete set of DNA, including all of its genes. Each genome contains all of the information needed to build and maintain that organism. Human Genome Project 1. 2. 3. 4. When did the Human Genome Project begin? Who was involved in the Human Genome Project? What is the Human Genome Project? What was the first step of the Human Genome Project? 5. How has advances in technology aided the Human Genome Project? 6. What are the benefits of the Human Genome Project? 7. What problems could arise from the Human Genome Project? Genotype vs Phenotype • An organism’s genotype is the set of genes that it carries. • An organism’s phenotype is all of its observable characteristics—which are influenced both by its genotype and by the environment. For example, differences in the genotypes can produce different phenotypes. In these house cats, the genes for ear form are different, causing one of these cats to have normal ears and the other to have curled ears. A change in the environment also can affect the phenotype. Although we often think of flamingos as being pink, pinkness is not encoded into their genotype. The food they eat makes their phenotype white or pink. DNA detective work Why can understanding a persons genome or even a large segment of their DNA be important: 1. Matching donor organs with recipients for transplants 2. Identifying suspects from DNA in evidence left at a crime scene 3. Exonerating people wrongly accused of crimes 4. Identifying victims in major accidents or natural disasters 5. Establishing paternity of a child Check Questions Pg 72 Dominant vs Recessive Genes Male Female The colour of the fish on the previous slide is controlled by a particular gene The gene comes in 2 forms: 1. Codes for black 2. Codes for red Alleles- Different versions of the same gene Even though the parents have the gene for red as well as black, the parents are still black This is because the black masks the red The gene for the black colour is said to be the dominant gene The gene for the red colour is said to be the recessive gene Homozygous (pure breed) Two copies of the same allele Heterozygous (hybrid) Two different copies of the same allele • Represents the dominant gene • Upper case • Preceeds the recessive gene • Represents the recessive gene (not r) • Lower case • Proceeds the dominant gene Always use the first letter of the dominant gene use the capital letter to represent the dominant allele use the lowercase letter to represent the recessive allele Predicting crosses It is possible to predict the type of offspring produced when 2 organism mate One of the easiest ways of predicting crosses is to use a Punnett square Pedigrees By studying family histories a pattern of inherited characteristics can be developed This pattern can be seen on diagrams called pedigrees Females Males Pedigrees can be used to work out the genotypes of individuals X-linked genes There are a number of genes on the X chromosome that have no equivalent on the Y chromosome These genes are X-linked The allele for normal colour vision is dominant A female who has an allele for colour-deficient vision on one X chromosome and an allele for normal colour vision on the other, will have normal colour vision. However she is called a carrier because she carries the affected gene for colour deficient vision A male who has an allele for colour-deficient vision on one X chromosome will be colour deficient Incomplete Dominance • When you have two alleles which are neither dominant or recessive • Instead they results as a mixture or a blend of the characteristic Co-dominance • When both allele or gene copies are produced Alleles (genotype) AA or Ao BB or Bo AB oo Blood type (phenotype) A B AB O Alleles A and B are co-dominant, allele o is recessive Check Qs Pg 80-81 Genetics Problems worksheet (Summative) Pedigree Worksheet Review Qs Pg 83-84 TEST