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4.1 Genetics: Chromosomes, Alleles, Genes, Mutations Genetics (the study of inheritance): The scientific discipline involved with studying how genes/traits are passed from parent to offspring. IB ASSESSMENT STANDARDS 4.1.1 State that eukaryote chromosomes are made of DNA and proteins. 4.1.2 Define gene, allele and genome. 4.1.3 Define gene mutation. 4.1.4 Explain the consequences of a base substitution mutation in relation to the processes of transcription and translation, using the example of sickle cell anemia. Genes and Alleles Gene: a heritable factor that controls a specific characteristic Located in specific places on chromosomes Humans have roughly 20,000-25,000 genes. Alleles: alternative forms of gene Example: Gene: eye color Alleles: blue vs. brown Genes Chromosomes Prokaryotes ‘Naked DNA’ Eukaryotic chromosomes Made of DNA and proteins Two Types: Two parts Autosomes (non sex chromosomes) Sex Chromosomes Sister Chromatids Centromere Homologous Chromosomes: chromosomes that have the same genes as each other, arranged in the same sequence, but not necessarily the same alleles of those genes Chromosome & Gene Numbers of Different Organisms Karyotyping A karyotype is a display (micrograph) of the number and type of chromosomes a nucleus contains. Cells are examined in metaphase of mitosis. The stained chromosomes are arranged according to size and structure. How are Karyotypes Useful? One of the main reasons for karyotyping is to find out whether a fetus has Down Syndrome or other chromosomal abnormalities. Karyotyping can be done by extracting and examining fetal cells (amniocentesis) or through chorionic villus sampling (examining cells from the placenta). Detecting Fetal Abnormalities Amniocentesis Chorionic Villus Sampling Mutations Mutations are changes in the sequence of bases in a gene. Changes in the sequence of bases cause changes to the amino acid sequences which change structure and function of the resulting protein. DNA Mutations vs. Chromosomal/Gene Mutations DNA Mutations Point Mutations Caused by base pair substitutions The replacement of one nucleotide and its partner with another pair Changes the amino acid the codon codes for and the protein Types: No effect: the amino acid sequence is not effected; protein not changed Missense: the codon codes for a different amino acid; protein changed Nonsense: the codon codes for STOP; protein changed DNA Mutations Frameshift Mutations Caused by inserting or deleting a nucleotide pair Changes the amino acid sequence from the point of the mutation to the end of the polypeptide chain Types: Nonsense: new base added creating a STOP; protein changed Missense: removal of a base creating new codons; protein changed Gene Mutations (Chromosomal) Deletion Duplication Reverses a segment within a chromosome Translocation Repeats a segment Inversion Removes a chromosomal segment Moves a segment from one chromosome to another nonhomologous one Alteration of Chromosome number Nondisjunction (we will discuss this more during Meiosis) Sickle-Cell Anemia (KNOW THIS) Normal hemoglobin has 4 subunits, 2 a chains and 2 b chains. A single base pair substitution can change the shape of the b chains, causing a sickle shape in red blood cells. Correct Base Pair Sequence: CTT (DNA) GAA (mRNA) Glu (amino acid) End result: normal hemoglobin, normal shaped cells Mutation Base Pair Sequence: CAT (DNA) GUA (mRNA) Val (amino acid) End result: abnormal hemoglobin and sickle shaped cells Sickle Cell Anemia (An Introduction) Hemoglobin Hemoglobin is found in red blood cells. The function of this protein is to carry oxygen throughout the bloodstream. All cells require oxygen for cellular respiration. Normal Hemoglobin Abnormal Hemoglobin Sickle-Cell Anemia Signs & Symptoms: Anemia Shortness of breath, dizziness, headaches, coldness in hands/feet, pale skin, jaundice. Pain Throughout the Body Blocked Blood Flow Infections Pulmonary Hypertension Stroke Multiple Organ Failure Mutation Practice (Sickle Cell Anemia) Sickle Cell/Protein Synthesis Handout The Most Unusual Mutations ‘Genome’ Genome: the whole of the genetic information of an organism The Human Genome Project Completed in 2003 The mapping of human chromosomes/genes. The Human Genome Project