front 1 Double Helix | back 1 A twisted ladder like structure composed of two strands of DNA. The sides of the double helix is composed of the sugar phosphate backbone. The phosphate of one nucleotide is bonded to the sugar of another nucleotide. The hydrogen bonds between the phosphates cause the DNA strand to twist. The nitrogenous bases point inward on the ladder and form pairs with bases on the other side like rungs.Each base pair is formed from two complementary nucleotides (purine with pyrimidine) bound together by hydrogen bonds. |
front 2 Nucleotide | back 2 A nucleotide is a molecule that is the building block of DNA and RNA. It is made up of three parts: a phosphate group, a five-carbon sugar, and a nitrogenous base. |
front 3 Hydrogen Bonds | back 3 The bonds that hold the base pairs together in the DNA sequence |
front 4 Sugar phosphate backbones | back 4 Sugars (deoxyribose) and phosphate groups are bonded by phosphodiester bonds, forming the ‘sides’ of the DNA ladder; giving the DNA its structure and formity. A sugar-phosphate backbone joins together nucleotides in a DNA sequence. |
front 5 Pyrimidine | back 5 A single ringed structure. The pyrimidine bases are Cytosine and Thymine. |
front 6 Purine | back 6 A double ringed structure. The purine bases are Adenine and Guanine. |
front 7 Thymine, cytosine, guanine, adenine | back 7 These are the four nitrogenous bases that make up DNA. They are found in pairs A-T, C-G. These base pairs are read in groups of 3, when the DNA is read to code for traits. If one of these bases are doubled, removed or incorrectly bonded like sometimes happens during mutation it alters the way the DNA is read. |
front 8 DNA | back 8 DNA is a polymer (single chain) made of nucleotides. Each nucleotide is made of a sugar (deoxyribose) connected to a phosphate group and bound to on the other side to a nitrogenous base (A, T, C, G). Our DNA guides the cell in making new proteins that determine all of our biological traits and gets passed (copied) from one generation to the next. |
front 9 Complementary base pairs | back 9 Adenine (A) and Thymine (T) are complementary, meaning they always pair together and Cytosine (C) and Guanine (G) are complementary. |
front 10 Alleles | back 10 A variation of a gene. These code for specific traits such as the colour of your eye and the colour of your hair. |
front 11 Genes | back 11 A strand/section of DNA that holds the instructions for one protein. This protein then codes for a specific trait. |
front 12 Chromosomes | back 12 Tightly wound DNA that contains the genetic information for an organism's characteristics. |
front 13 Chromatids and chromatin | back 13 Chromatids are what chromosomes are called during cell division, when they are linked by the centromere. They are identical halves of a chromosome, called sister chromatids. |
front 14 Homologue and homologous pair | back 14 Two members in each pair of chromosomes with similar size & shape, centromere in the same place, identical genes at same locus but may be different alleles |
front 15 Maternal paternal | back 15 Maternal means that it is passed down from the mother and paternal means that it is passed down from the father. |
front 16 Genetic variation | back 16 Genetic variation is naturally occurring genetic differences among individuals of the same species. This variation can increase the chance of survival of a species should their environment change. Genetic variation can be caused by lots of different factors such as migration, genetic drift, Natural selection, mutation, sexual reproduction (meiosis). |
front 17 Causes of Variation | back 17 Non-heritable variations are those caused by the environment. (mutations) Heritable variations are those which are inherited from parents (sexual reproduction-meiosis) All the many characteristics which make up an individual, including its appearance, are called its phenotype. Each phenotype is a blend of heritable and non-heritable characteristics. Mutation as the ultimate source of genetic variation within the gene pool. |
front 18 Consequences of mutations | back 18 Mutations usually have negative impacts on a phenotype, but occasionally they can act positively, for instance, by improving the individual's fitness in its environment. This means they will be “selected for” and so increase in frequency in a population. |
front 19 Mutations | back 19 A randomly occurring permanent change to the base sequence in the DNA in a gene or chromosome that may create new alleles. Mutations are the only way new alleles are formed and so are known as “the ultimate source of variation”. Without mutation there would be no variation, and without variation there would be no evolution. |
front 20 Heritable | back 20 The passing on of particular traits from an individual to its offspring |
front 21 Mutagen | back 21 Something that speeds up the process of a mutation. mutagens can include chemicals, UV rays (i.e. sunlight) and radiation (i.e. x-rays and radioactive materials). Affect the nucleotides themselves: converting one base to another, knocking a base off its backbone, or even causing a break in the DNA strand. |
front 22 Gametic | back 22 Gametic is the sex cells eg egg, sperm. They contain half the normal amount of genetic material (23 chromosomes) the genetic material contained within the gametic cells can be passed on to another generation through reproduction. Any mutations that occur in these cells can be passed on. |
front 23 Somatic | back 23 Somatic is the cells in the body containing 46 chromosomes. Somatic mutations are not passed on from one generation to the next. Somatic mutations only affect the individual organism in which the cells have mutated because body cells are not inherited |
front 24 Evolution | back 24 Evolution is the slow development/change in a species genetic material. Evolution is often to help a species survive in a certain environment or adapt to a new predator or threat. It takes place over many generations and the change in traits are carried on through reproduction. |
front 25 Natural selection | back 25 Genetically varied species have different traits which may be better suited to a change in the environment. The individuals with the favourable traits will go on to reproduce, meaning that their offspring will inherit the favourable trait. Those with unfavourable traits will die due to the change in environment and therefore will not be able to reproduce. Therefore, the trait is removed from the genepool, increasing the chances of survival of the species. Driving force of evolution. |
front 26 Monohybrid Cross | back 26 A breeding experiment where we are considering only one characteristic. |
front 27 Frameshift | back 27 Insertions and deletions can alter a gene so that its message is no longer correctly read. |
front 28 Substitution | back 28 Mutation that exchanges one base for another (i.e., a change in a single "chemical letter" such as switching an A to a G). |
front 29 Insertion | back 29 Mutations in which extra base pairs are inserted into a new place in the DNA. |
front 30 Crossing over | back 30 An exchange of genetic material between adjacent chromatids of homologous chromosomes during meiosis. results in novel combinations of alleles on the chromosomes, creating almost infinite potential for variation. |
front 31 Independent assortment | back 31 When each of the 23 chromosome pairs line up during the first phase of meiosis completely randomly before the cell splits, leading to genetically different daughter cells. |
front 32 Random segregation | back 32 During meiosis, pairs of alleles are segregated when the homologous chromosomes split so that each gamete only receives one allele for each pair. Segregation results in all daughter cells being unique. |
front 33 Deletion | back 33 Mutations in which a section of DNA is lost, or deleted. |
front 34 Causes of Variation in sexual reproduction | back 34 Crossing Over |
front 35 Diploid/Haploid | back 35 In humans, diploid cells contain 46 chromosomes whilst haploid cells only contain half of this number (23 chromosomes). Generally, all cells in the human body (except red blood cells and gametic cells) are diploid cells. Whilst the sperm in men and eggs in women contain 23 chromosomes. |
front 36 Histones | back 36 The proteins which DNA is tightly bound to in chromostins. |
front 37 Centromere | back 37 The centromere links a pair of sister chromatids together during cell division. |
front 38 Locus | back 38 Refers to the location on the chromosome where the gene is found. SInce most organisms have two sets of chromosomes, they have (except on the sex chromosomes) two alleles at each gene locus. |
front 39 Autosomes | back 39 One of the numbered chromosomes, as opposed to the sex chromosomes. Humans have 22 pairs of autosomes and one pair of sex chromosomes (XX or XY). Autosomes are numbered roughly in relation to their sizes. |
front 40 Sex Chromosomes | back 40 A type of chromosome involved in sex determination. Humans and most other mammals have two sex chromosomes, X and Y, that in combination determine the sex of an individual. |
front 41 Allele Frequency | back 41 How common an allele is in a population |
front 42 Chiasma | back 42 A structure that forms between a pair of homologous chromosomes by crossover recombination and physically links the homologous chromosomes during meiosis. |
front 43 Complete Dominance | back 43 The dominant allele completely masks the effect of the recessive allele in the heterozygous condition. |
front 44 Incomplete Dominance | back 44 When the two alleles combine to create an intermediate or blended phenotype |
front 45 Codominance | back 45 When both alleles are expressed separately. Human blood type is a good example of this. |
front 46 Phenotype | back 46 A description of the appearance of an organism. Any characteristic can have several phenotypes, e.g. a daffodil can have a yellow flower colour or orange flower colour or white flower colour. |
front 47 True Breeding | back 47 An individual with a homozygous genotype. |
front 48 Gentotype | back 48 Tells us which allesles are present. |
front 49 Why Phenotypic Ratio is Not Achieved | back 49
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front 50 Multiple Alleles | back 50 Genes have more than two allelic forms. |
front 51 Lethal Alleles | back 51 Alleles that cause the death of the organism that carries them. They are usually a result of mutations in genes that are essential for growth or development. Recessive lethal alleles only kill homozygotes. Lethal alleles are often detected as the ratio of expected progeny is distorted |
front 52 Test Cross | back 52 Performed in order to decide the genotype of a dominant appearing parent. Breed an individual with a known genotype with a individual with a dominant phenotype to see if the individual is hetrozygous or homozygous dominant. |
front 53 Dihybrid Cross | back 53 Dihybrid cross is a cross between two individuals with two observed traits that are controlled by two distinct genes |
front 54 Linked Genes | back 54 Two genes that occur on the same chromosome are said to be linked, and those that occur very close together are tightly linked. the observed ratio will be quite different from that seen for unlinked traits. Allele combinations that began together will tend to stay together, and the offspring will show a skewed ratio reflecting the original combinations. If the loci for the two genes are very close, crossing over is unlikely to separate alleles, whereas if they are far apart, crossing over is much more likely to separate them. They do not assort independently, whereas genes located on different chromosomes assort independently and have a recombination frequency of 50%, linked genes have a recombination frequency that is less than 50%. |
front 55 Genetic Change | back 55 The change in frequency of alleles in the gene pool of a population |
front 56 Gene Pool | back 56 Total number of alleles that exist for a population |
front 57 Populations | back 57 A group of individuals of the same species in the same place at the same time. |
front 58 Genetic Drift | back 58 Change in the allele frequencies of populations due to a chance event. Alleles can be lost from the gene pool. Like migration, genetic drift is most likely to affect smaller populations. This is not a form of natural selection as they don't disappear from the gene pool due to lack of fitness but rather due to chance |
front 59 Founder Effect | back 59 Occurs when a small group of individuals colonizes a new isolated area. They form the founder population. The range and frequency of alleles in the founder population is unlikely to be representative to that of the original population. Some alleles might not be present at all in the founder population whereas others might be more or less frequent. |
front 60 Bottleneck Effect | back 60 Occurs when a population may be suddenly reduced in numbers to a small size. The population numbers then increase but diversity has been lost s the survivors are all descended from the small group that came through the bottleneck. This can be the result of: a catastrophic environmental event or a human action. As individuals are removed their alleles are removed from the gene pool. This results in changes in allele frequencies. The population will have reduced biodiversity. |
front 61 Migration | back 61 The movement of individuals from one population to another (can reduce genetic diversity) |
front 62 Immigration | back 62 Individuals coming in (can increase genetic biodiversity if a new allele comes in) |
front 63 Emigration | back 63 Individuals leaving |
front 64 Stabilising Selection | back 64 Maintains the population in a stable form by favouting the average and selecting against the extremes in either direction. |
front 65 Directional Selection | back 65 Favors the phenotype of one extreme, so that there is a shift if the average, so there is a shift of the average in one extreme, therefore a shift in one direction. |
front 66 Disruptive Selection | back 66 Favors both extremes at the expense of the average. |