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Responding to ill Health Life Science Cells (genetic inheritance & cancer) US Dept Energy (2005) https://commons.wikimedia.org/wiki/File:Dna-split.png 1 Learning outcomes Summarise the role of chromosomes & genes in the inheritance of characteristics Discuss the differences between meiosis and mitosis in relation to chromosome numbers Explain the terms: dominant, recessive, co dominant, sex linked Explain the terms mutation and carcinogenesis and outline the modes of cancer spread 2 Introduction Genetics - the study of heredity information transmitted via genetic material (DNA) DNA in cell nucleus, visible as chromosomes during cell division Gene = piece of DNA associated with particular characteristic, acts as template for protein synthesis 3 How a protein is made DNA in nucleus proteins synthesised by ribosomes in cytoplasm information passed from DNA to ribosomes via RNA 4 DNA and proteins A protein = a chain of amino acids in a particular sequence Approx 20 different amino acids DNA determines which amino acids are made via a “genetic”code 5 Genes All body cells have the same genes Different genes are ‘expressed’ in different cells e.g gene coding for insulin is expressed in certain cells of pancreas ( cells, islets of Langerhans ) Genes coding for enzymes which break down glucose expressed in virtually all body cells NB importance of gene expression in right cells, in right amounts at right times 6 Cells and chromosomes Normal body cells diploid (46 chromosomes) 23 homologous pairs i.e. 2 copies of each chromosome Half inherited from father and half from mother Sum total of chromosomes = karyotype Cells and chromosomes 22 autosomes (nos 1 -22) Sex chromosomes (no 23) Male XY Female XX National Cancer Institute (2007) Karyotype_(normal). https://commons.wikimedia.org/wiki/File:Karyotype_(normal).jpg meiosis Eggs and sperm must have half the number of chromosomes of a normal body cell (23 instead of 46 – one member of each homologous pair) Why? ……………….. achieved via a special type of cell division meiosis errors in meiosis may chromosome abnormalities 9 Alleles and genes One copy of each gene = one maternal & one paternal Alleles - different versions of the same gene Site of a gene = locus At one particular locus on homologous pair , genes code for the same trait gene Allele A A a B B Allele a UWS Staff (2015) 10 Dominant & recessive traits alleles may be : dominant ( CAPITAL LETTER) recessive (lower case letter) e.g. E = unattached earlobe e = attached earlobe EE http://www.rrnursingschool.biz/unity-companies/genes-and-alleles.html ee 11 Dominant & recessive traits everyone has 2 of these alleles, therefore 3 possibilities: EE Ee Ee Homozygotes & heterozygotes Individuals with: EE or ee are homozygotes (2 copies of the same allele) Ee are heterozygotes (2 different alleles) genotype phenotype EE unattached Ee unattached ee attached 12 Cell division & reproduction gametes Stannered (2007) https://commons.wikimedia.org/wiki/File:Sexual_cycle.svg Human Life Cycle • half paternal genes • half maternal genes Parents children only physical link • sperm/ova produced by meiosis half number of chromosomes (n = 23: haploid) • all other cells have 46 (2n = 46: diploid) • sperm + ovum unite diploid zygote mitosis many diploid daughter cells embryo: 13 Predicting genotypes & phenotypes of children Each gamete (egg/sperm) receives: one copy of each chromosome & one allele of each gene e.g. parent with EE genotype all gametes have E allele Parent with Ee genotype 50% of gametes have E allele 50% of gametes have e allele 14 Example • • • • father’s genotype Ee – phenotype? unattached different types of gamete? 50% E ,50% e • • • • mother’s genotype ee – phenotype? attached different types of gamete? all e Example – Punnett’s Square to predict progeny continued • Ear lobe attachment of children? father E e e Ee ee Ee ee mother e • Probability of having a child with attached earlobes • 50% 1. Autosomal dominant disorders Only one copy of allele needed for individual to be affected Example 1 - Neurofibromatosis Tumour-like growths on skin gene on chromosome 17 variable expressivity 17 1. Autosomal dominant - neurofibromatosis Nicke.me (2011) https://commons.wikimedia.org/wiki/File:Dermal_Neurofibroma.jpg 18 Autosomal Dominant Disorders Prediction example – neurofibromatosis • • • • father’s genotype Nn – phenotype? neurofibromatosis different types of gamete? 50% N ,50% n • • • • • • mother’s genotype ? nn phenotype? normal different types of gamete? all n Example - continued • Possible genotypes of children? mother n n N Nn Nn n nn nn father Probability of having child with neurofibromatosis? 50% Autosomal dominant disorders Example 2 - Huntingdon disease degenerative brain disorder gene on chromosome 4 faulty production of neurotransmitter (GABA) uncontrolled movement impaired speech, dementia late onset Why is late onset a problem? Sufferer may already have reproduced before disease becomes apparent 21 Autosomal recessive disorders 2 alleles of abnormal gene disease 1 allele of abnormal gene = ‘carrier’ Examples: Cystic fibrosis 1 in 2000 births, (1 person in 22 = carrier) Thick viscous mucus (chloride ion channels faulty) PKU 1 in 5000 births enzyme lacking for breakdown of phenylalanine Accumulation mental retardation Babies put on diet low in phenylalanine until brain fully developed (7yrs) 22 Sex linked inheritance XY = male XX = female Male determines sex of child (always an X chromosome from mother) X chromosome larger than Y Alleles on X chromosome may not have equivalent on Y Sex linked inheritance Male has only one X chromosome (this is referred to as being hemizygous) and must therefore express the alleles on that chromosome, whether they are dominant or recessive. Female has two X chromosomes: A female needs two copies of an X-linked recessive allele to express it, a male needs only one Sex linked inheritance X –linked recessive disorders Men cannot be carriers, women can. Many more men than women likely to be affected by the disorder 25 Example – red-green colour blindness X C = normal vision, X c = colour blind • man’s genotype? • X CY • phenotype? • normal • different types of gamete? • 50% X C 50% Y • • • • • • mother’s genotype ? X CX c phenotype? carrier different types of gamete? 50% X C 50% X c Example - continued Chances of colour-blind boy? • possible genotypes of children ? Chances of colour-blind girl? mother XC XC XC XC Xc X CX c father Y Y XC YXc Mutations & disorders Mutations (changes in sequence of DNA bases) may result in changed properties of proteins for which they code caused by e.g. errors of ‘copying’ environmental factors heritable if in germ cells not heritable if in body cells (somatic mutations) 28 Regulation of genes A complex subject! Genes are switched on or switched off as appropriate e.g. Certain genes are switched on to stimulate cell division When adequate growth has been achieved other genes are switched on to inhibit cell division 29 Mutations & cancer Cancer occurs when gene mutations uncontrolled growth & division of cells Several mutations needed over many years Process of cancer development = carcinogenesis 30 Carcinogens Carcinogens – agents which predispose to tumour development Cause mutations in the genes that control normal cell growth & development Can be: Chemical Physical viral 31 Cancer Tumour (neoplasm) may be benign or malignant Malignant tumour = cancer Normal cells are differentiated (resemble parent cell) Cancer cells usually undifferentiated (do not resemble cell from which they were derived) 32 Cancer 33 Some tissues more affected by metastatic spread: LUNGS pulmonary circulation LIVER hepatic portal circulation BRAIN, KIDNEY, BONE – large blood supplies 34