Sickle Cell Anemia Study Guide PDF

Preparation for the Genetics Variation Assessment Introducing the Standard “Demonstrate understanding of genetic variation in relation to an identified characteristic” Candidates will produce a report during the exam time. There will be two parts to the report, both providing opportunity for can...

Preparation for the Genetics Variation Assessment Introducing the Standard “Demonstrate understanding of genetic variation in relation to an identified characteristic” Candidates will produce a report during the exam time. There will be two parts to the report, both providing opportunity for candidates to demonstrate their understanding of genetic variation in relation to an identified characteristic: Part A: Candidates will choose a context. The context chosen should ensure there is gene coding for a single characteristic that can be investigated. Context choices that also include a known mutation in the gene should support the evaluation of genetic variation. Examples of contexts could include: kiwi, kākāpō, longfin eel, whio (blue duck), Sickle Cell Anaemia Part B: Candidates will respond to a context provided. Approx 800 words in total スタンダードの紹介 "特定された特性に関する遺伝的変異について理解を示す" 受験者は試験時間中にレポートを作成する。 レポートには2つのパートがあり、どちらも 受験者が特定された特徴に関連する遺伝的変異について理解を示す機会となる： パート A ： 受験者は文脈を選択する。 選択する文脈は、調査可能な単一の特性をコー ドする遺伝子が存在することを確認するものでなければならない。 また、その遺伝子に 既知の変異を含む文脈を選択することで、遺伝的変異を評価することができる。 文脈の 例としては、キウイ、カーカーポ、ロングフィン・ウナギ、ウィオ（ア オガモ）、鎌状赤血球 貧血などが挙げられる。 パート B ： 受験者は与えられた文脈に答える。 合計約800語 1 - Where does variation come from? Part of your discussion about variation for your assessment includes what causes it. Here is a reminder of what you have learned about where and how variation happens. 1 - Mutation. A permanent change in the DNA base sequence. You learnt about this in the M&Ms activity - how some mutations have no effect (a silent mutation) or can create a new allele (a nonsense mutation). THIS IS THE ONLY WAY NEW ALLELES ARE MADE. 2 - Meiosis. Cell division to produce gametes. The variation from meiosis comes about by mixing pre-existing alleles. 1 - Where does variation come from? 2 - Meiosis (contd) - the 3 sources of variation Crossing Over - swaps over the alleles from homologous chromosomes so that the combination of alleles on each chromosome is different Independent Assortment - chromosomes line up randomly so each gamete has a different mix of paternal and maternal - over 8m possible combinations Segregation - allele pairs are separated randomly This means that every sperm and every egg is unique. 3 - Fertilisation - A random egg and a random sperm join together- to form a VERY unique zygote Mutation, Meiosis and Fertilisation - ALL work together to create variation in a population. Meiosis and Fertilisation are both part of sexual reproduction 1 - Where does variation come from? Complete the activity in your workbook - answering those questions will help in your preparation for your External. Describe genetic variation. Explain how sexual reproduction causes genetic variation. In your answer, you should consider: The process of gamete formation Fertilisation 2 - What is Gene Tracking? Another important part of a discussion around genetic variation should be about tracking that variation through generations. A method for determining the inheritance of a particular gene in a family or population. Examples: Pedigree Chart Gel Electrophoresis Punnett Squares Punnett Squares A way of predicting possible offspring from a cross (2 individuals mating) It also predicts the expected ratio of those offspring BUT it is a prediction and real life is different - how many of you have/know of families with all boys or all girls although the prediction would be 50:50 2 - What is Gene Tracking? The outside (top and side) panels are the gametes from the two parents - think back to the meiosis activity The boxes inside are the fertilised eggs (zygotes) - the result of the fusing of the two gametes 2 -What is Gene Tracking? Pedigree Charts Punnett Squares predicts what will happen, Pedigree Charts state what ACTUALLY happened Case Study - Sickle Cell Anaemia Sickle Cell Anaemia is one of the context that you can choose for your external assessment But the chosen context is only half of the assessment - everything else we have done in the last few weeks may also help you The context should have - 1 organism (human), 1 gene (the gene for haemoglobin) and 1 mutation (the sickle cell mutation) Case Study - Sickle Cell Anaemia Genetic disease - Anaemia (Reduced Oxygen levels in the blood), Pain, Lethargy, Blindness, Organ dysfunction as the cells get trapped in capillary beds Mutated version of the gene that helps make haemoglobin — a protein that carries oxygen in red blood cells Is a really good demonstration of studying DNA and genes Case Study - Sickle Cell Anaemia Due to that one change in the amino acid sequence there is a change in the shape of the haemoglobin - so the molecules clump together Oxygen cannot be taken up as readily by the haemoglobin The cells take on a sickle shape - hence the name of the disease. Case Study - Sickle Cell Anaemia Tracing the sickle cell mutation The mutated sickle cell allele is a recessive allele r. Unusually, the three different genotypes of the sickle-cell disease (RR, Rr and rr) have three different phenotypes. This means we can trace the chances of getting the disease or being a carrier from Punnett Squares Case Study - Sickle Cell Anaemia WHY DOES THE SICKLE CELL MUTATION CONTINUE IN THE POPULATION? Because of the symptoms of Sickle Cell Anaemia, the death rate of those with sickle-cell disease is particularly high in children: 15.3% for infants 36.4% for under 5s 43.4% for under 10s Average life expectancy is around 14 (before child-bearing age) - unless you have medicine SO, you might ask - “why hasn’t the mutated allele been eliminated?” Case Study - Sickle Cell Anaemia Look at these two maps of Africa. What do you notice? Answer the questions in your workbook about the Africa Maps Case Study - Sickle Cell Anaemia 3 Phenotypes Homozygous Dominant (RR) - no disease, no carrier Homozygous Recessive (rr) - full blown disease, death before 14 Heterozygous (Rr) - no disease but a carrier. Called Sickle Cell Trait. No other symptoms BUT gives increased resistance to malaria Malarial parasites invade normal red blood cells Parasites breed and make red blood cells sticky Case Study - Sickle Cell Anaemia Sickle Cell Trait doesn’t affect the haemoglobin as drastically as full blown Sickle Cell Disease Haemoglobin does become misshapen and this affects a parasite’s ability to complete life cycle Parasite triggers the Sickle Cell Trait haemoglobin to sickle The immune system then clears the infected red blood cells Fewer parasites, milder illness So having Sickle Cell Trait is a survival advantage in some parts of the world The Genetic Variation provided by this mutation offers a survival advantage Case Study - Sickle Cell Anaemia The Sickle Cell Mutation is now fixed into the population: