Core Biology - Topic 1 Inheritance 3.0 / 5 based on 1 rating ? BiologyDNA and inheritanceGCSEEdexcel Created by: KatieCreated on: 14-04-13 22:08 Genes Variration caused by genes is inherited variation 3 main parts of most cells - cell membrane, cytoplasm, nucleus Inside the nucleus - long strands of substance called DNA Each strand forms a structure called a chromosome (with protein) Chromosomes are divided into genes Each chromosone carries a large number of genes that do particular jobs Many genes control our variations e.g. eye colour, hair colour, face shape Alleles - Different forms of the same gene may contain slightly different instructions these create the variations like eye colour 2 copies of every chromosome in the body's cell nuclei 2 copies of every gene each copy could be a different allele Different organisms have different numbers of chromosomes humans have 23 pairs containing roughly 23,000 different genes in total Many alleles for each gene so we all inherit slightly different characteristics 1 of 4 Explaining Inheritance All plants and animals produce gametes (sex cells) Male gametes - sperm cells (animals) pollen grains (plants) Female gametes - egg cells (animals and plants) Gamates different to most body cells only have one copy of each chromosome therefore gametes only have one allee per gene 2 gamates fuse together in sexual preproduction the new organism contains two alleles for each gene (one each from male & female) Each allele from the parents is either dominant or recessive If a dominant is present, the recessive will have no effect so a recessive characteristic is only seen if both alleles are recessive Dominant alleles are shown with a capital letter - recessive same letter but lowercase Genotype - the alleles in an organism Phenotype - what the organism looks like Homozygous - both alleles for gene are the same Heterozygous - alleles are different 2 of 4 Punnett Squares Possible genotypes are shown in a Punnett square To work out the probability of each phenotype occuring if 2 organisms breed 3/4 chance of A characterisic - 0.75 / 75% / 3:1 probabilty 3 of 4 Genetic Disorders Genetic disorder - a disease caused by faulty alleles faulty allele is recessive - suffers must have 2 copies Sickle cell disease - sickle shaped red blood cells suffers become tired easily and short of breath painful joins when red blood cells stick together and block blood vessels blocked blood vessels can sometimes be fatal Cystic fibrosis - mutation with the gene that creates sweat, mucus and digestive juices lungs get clogged with thick sticky mucus so difficulty breathing results in debris entering lungs causing infections mucus also blocks some tubes that carry enzymes to the small intestines this lack on enzymes results in weight loss Doctors use pedigree charts (key family tree) for: understanding how genetic disorders are inherited working out the probability of inheritance PEDIGREE ANALYSIS Genetic screening can be done for couple's who know a genetic disorder is likely 4 of 4
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