Inheritance, Variation and Evolution

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males Describe the process of meiosis. 1. before the cell divides, it duplicates its genetic material which arrange in pairs in the centre of the cell 2. in the first division, two cells are made. each cell has one copy of the chromosome pairs 3. in the second division, the chromosomes line up again and the centre and the chromosome pairs are pulled apart 4. four gametes with one set of chromosomes are produced. they are random and all are genetically different ▾ What happens to these daughter cells? Unit 6 - Inheritance, Variation and Evolution 2 they fertilise with the opposite sex gametes to produce cells with 23 chromosome pairs these cells divide by mitosis to produce an embryo the cells then become specialised to form other cells (Muscle and nerve cells etc) DNA ▼ What does DNA stand for? deoxyribonucleic acid ▼ Where is DNA found? in the nucleus of animal cells, in long strands of chromosome pairs ▼ What is the structure of DNA? double helix ▼ Genes What is a gene? a small section of DNA in a chromosome What is the function of a gene? codes for a particular sequence of amino acids that are put together to make a specific protein ▼ How many amino acids are used in this sequence? 20 ▼ What allows different cells to be produced via proteins? DNA - determines the type of protein which determines the type of cell ▾ Genomes What is a genome? an entire set of genetic material of an organism ▾ How does scientists studying the entire genome allow advancements in medicine? • allows scientists to identify genes linked with different diseases Unit 6 - Inheritance, Variation and Evolution 3 knowing what genes cause different diseases allows scientists to learn more and develop treatments for them • discovering human migration patterns ▾ The Structure of DNA ▾ What are the repeating units of DNA called? nucleotides - DNA is a polymer ▾ What does each repeating unit consist of? a phosphate, a sugar and a base ▼ The sugar and phosphate groups form the... backbone to the DNA strands ▼ What are the four bases called? A, T, C and G ▾ What is complementary base pairing? when each base links to a specific base on opposite sides of the helix ▾ What are these base pairs? A+T C +G What does the order of bases determine? the order of amino acids in the protein ▼ How many bases does it take to code an amino acid? 3 ▼ What do parts of DNA that don't code for proteins do? they control whether or not a gene is expressed (used to make a protein) ▼ Protein synthesis ▼ Explain the stages of protein synthesis 1. transcription- a copy of a gene is made in the nucleus- called a template (mRNA) 2. mRNA passes out of the nucleus and into the cytoplasm 3. translation- mRNA molecules attach to a ribosome Unit 6 - Inheritance, Variation and Evolution 4 4. amino acids are brought to the ribosomes and bind to carrier molecules (tRNA) 5. ribosomes read the triple bases of mRNA and code for different orders of amino acids 6. when complete, it folds into a specific shape ▼ What are the functions of these proteins? enzymes hormones structural proteins ▼ Genetic Mutations ▼ How do mutations occur? can be inherited, or just randomly occur What factors increase the chance of a mutation occurring? exposure to certain substances or types of radiation ▼ How do mutations affect the protein formed? mutations change the sequence of DNA bases in a gene produces a genetic variant these sequences code for a protein so a change in the protein is formed ▾ What happens in serious cases of mutations? enzyme active sites can be altered so cannot fit the substrate structural proteins (eg collagen) could lose their strength ▾ Different Types of Mutations Insertions when a new base is inserted into a DNA base sequence which changes the way the 3 bases are read which changes the amino acid (can change more than one amino acid) ▼ Deletions when a random base is deleted which changes the way the base sequence is read Unit 6 - Inheritance, Variation and Evolution 5 (can change more than one amino acid code) Substitutions when a random base is changed to a different base eg T become A Define these words: ▼ gamete reproductive cells chromosome thin strands of DNA ▼ gene small section of chromosome allele different versions of the same gene ▼ dominant a type of allele that is always expressed, even if there is only one of it recessive only expressed if the person has two copies of it ▾ homozygous both identical for the same characteristic (eg pp or PP) heterozygous both different for the same characteristic (eg Pp) genotype combinations of alleles that determine your characteristics ▾ phenotype observable characteristics ▼ Inherited Disorders ▾ Cystic Fibrosis ▼ What is cystic fibrosis? Unit 6 - Inheritance, Variation and Evolution 6 genetic disorder of the cell membrane, produced thick, sticky mucus in the air passages and pancreas ▼ Which allele is it caused by? recessive alleles ▼ How many recessive alleles do you need? two recessive alleles How do you become a carrier of cystic fibrosis? one recessive alleles ▾ Polydactyly ▼ What is it? having extra fingers or toes ▼ What allele is it caused by? a dominant gene ▾ How do you become a carrier? impossible - having one dominant allele 'D' will cause polydactyly Embryo Screening Definition extracting DNA from an embryo and analysing its genes to determine if it has an inherited disorder ▾ Advantages help stop suffering of child and parents Disadvantages expensive some think it should be used somewhere else a large number of embryos are created but only a small amount is planted some healthy die - unethical could be used to create a desirable baby eg hair colour - unethical ▼ Sex Determination ▼ Chromosome Pairs ▼ Male Unit 6 - Inheritance, Variation and Evolution 7 XY ▼ Female XX 4.6.2 Variation And Evolution ▾ Types of Variation ▼ Define variation Differences in the characteristics of individuals in a population ▾ What is genetic variation? combining of genes from two parents ▾ What is environmental variation? conditions affect a person's phenotypes ▼ What is a combination of both? a person's genes determine their phenotype but their environment determines if that is carried out eg height and diet ▼ Why don't species look exactly alike? mutations cause variations ▾ Do mutations affect the organism's phenotype? most have no effect on the phenotype some influence phenotype very few determine phenotype ▼ What happens to the phenotype when the environment changes? if the phenotype means the individual is more suited to their environment, it can lead to a relatively rapid change in the species ▼ Selective Breeding ▼ What is selective breeding? the process by which humans breed plants and animals for particular genetic characteristics ▼ How does it work? Unit 6- Inheritance, Variation and Evolution 8 involves choosing parents with desired characteristics from a mixed population and breeding together so the offspring inherits the characteristic ▼ Examples of useful characteristics in plants and animals: disease resistance in food crops animals which produce more meat or milk domestic dogs with gentle nature large or unusual flowers to sell ▾ What is a disadvantage of selective breeding? can lead to inbreeding - where some breeds are prone to disease or inherited defects ▼ Why does this disadvantage occur? reduction in the number of different alleles so gene forms are too similar ▾ Genetic Engineering ▾ Define genetic engineering a process which involves modifying the genome of an organism by introducing a gene from a different organism to give a desired characteristic ▼ How does this work? genes from the chromosomes of the organism are cut out using enzymes and inserted into a vector (bacterial plasmid or virus) this vector is used to insert the gene into required cells they're transferred to cells at an early stage in development so they develop with desirable characteristics ▾ Give some examples of genetic engineering in industry. bacteria - genetically modified to produce human insulin to treat diabetes crops - genetically modified to improve size and quality, and resistant to disease gene therapy - treating genetically inherited diseases ▾ What are some dilemmas of genetic engineering? changing an organisms genes might accidentally create problems which could be passed onto future generations Unit 6 - Inheritance, Variation and Evolution 9 ▼ Pros and Cons of Genetic Engineering ▼ Pros GM crops increase yield GM crops give some populations the needed nutrients GM crops are already being grown without any problems ▼ Cons • can reduce farmland biodiversity - growing GM crops can affect the number of wildflowers and so habitats for insects • some people think they're not safe to eat - may develop allergies (they think) • transplanted genes may get out into the natural environment ▼ Cloning Plants Tissue Culture ▼ How can plants be cloned from tissue culture? a few plant cells are placed in a growth medium with hormones and grow into new cloned plants Why do scientists clone plants from tissue culture? used to preserve rare plants that hard to reproduce naturally, to produce stock quickly ▾ What are the advantages of cloning plants from tissue culture? can be made quickly don't require lots of space ▼ Cuttings ▾ How can plants be cloned from cuttings? gardeners take cuttings from good parent plants and plant them to produce genetically identical copies ▾ What are the advantages of cloning plants from cuttings? can be made quickly cheap Unit 6 - Inheritance, Variation and Evolution 10 ▾ How do embryo transplants work? sperm cells and egg cells are taken from the animals the sperm artificially fertilises the egg the embryo develops then is split before the cells become specialised these are implanted into the animal ▾ How does adult cell cloning work? • the nucleus is removed from an unfertilised egg cell • the nucleus of an adult body cell, such as a skin cell, is inserted into the egg cell • These embryo cells contain the same genetic information as the adult skin cell • An electric shock stimulates the egg cell to divide to form an embryo • When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development ▾ What are the issues surrounding cloning? ▼ Pros • can preserve endangered species - retains biodiversity • could lead to a greater understanding of the development of the embryo, aging and age-related disorders • increase yield of plants and animals • able to make clones of animals that can have medical advantages Cons • could lead to a reduced gene pool and therefore could lead to extinction if a disease breaks out + mutations • cloned animals might not be as healthy as regular animals • some people worry that humans could be cloned which leads to defect eg severely disabled children • ethical issues - exploiting the animals Unit 6 - Inheritance, Variation and Evolution 11 4.6.3 The Development of Understanding of Genetics and Evolution ▼ What does the theory of evolution and natural selection state? all of today's species have evolved from simple life forms that first started to develop over three billions years ago ▼ What is evolution? a change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species ▾ What is 'survival of the fittest'? organisms with the most suitable characteristics for the environment would be more successful and more likely to survive, then passing on those characteristics - creates more desirable offspring ▾ Why was his theory only gradually accepted? went against common religious beliefs - rejected God insufficient evidence at the time the theory was published to convince many scientists mechanism of inheritance and variation was not known until 50 years after the theory was published. ▼ Speciation ▼ What is speciation? development of a new species from the same species in different populations ▼ Process of Speciation two populations of the same species physical barriers separate populations populations adapt to new environments development of a new species ▼ How can the isolation of a species occur? due to a physical barrier eg flood and earthquakes Unit 6 - Inheritance, Variation and Evolution 12 ▾ Why does speciation occur? conditions of both environments are different (different climates) individuals with characteristics that make them better adapted to their environment are more likely to survive they're more likely to breed and pass on this beneficial characteristic ▼ What work is Wallace most famous for? speciation warning colours ▼ Mendel ▾ What experiment did Mendel carry out? took two crosses for height of pea plants First Cross Tall + Dwarf = All tall pea plant offspring Second Cross Tall Tall Three tall + One Dwarf pea plant offspring ▼ What was his conclusion from this? characteristics in plants are determined by hereditary units hereditary units are passed on to the offspring, one unit from each parent hereditary units can be dominant or recessive - if the individual has both recessive and dominant alleles, the dominant characteristic expressed ▾ Why was his work only recognised after his death? • lack of knowledge of genes, DNA and chromosomes • late 1800s - scientists learned about chromosomes and cell division • early 20th - similarities between chromsomes and Mendel's units. units were found on chromosomes and are now called genes • 1953- structure of DNA is determined ▼ Lamarck ▼ What was Lamarck's theory of evolution? if an organism uses a specific characteristic the most, it would be passed down and inherited by its offspring ▾ Why was his theory eventually rejected? Unit 6- Inheritance, Variation and Evolution 13 experiments did not support his hypothesis ▼ Fossils ▼ What are fossils? remains of organisms from thousands of years ago ▼ What can fossils tell scientists today? how much or little organisms have evolved over time ▼ How can fossils form in rocks? ▼ gradual replacement by minera parts of the organism which doesn't decay easily can last a long time when buried They become replaced by minerals as they decay, forming a rock-like substance surrounding sediment turns to rock but the part stays distinct casts and impressions when an organism is buried in soft material, it hardens and the organism decays leaves a cast of itself eg footprints, plant roots preservation in places where no decay happens in some places there is not oxygen or moisture so microbes cannot survive so decay cannot occur ▼ How are scientists still uncertain about how life began? many were soft-bodied and soft tissue decays completely - so no evidence fossils could have been destroyed due to geological activity eg movement of tectonic plates Extinction ▼ What is extinction? when there are no remaining individuals of a species still alive ▼ What factors affect extinction? environment changes too quickly Unit 6 - Inheritance, Variation and Evolution 14 a new predator kills them all a new disease kills them cannot compete with other species for food a catastrophic event occurs to kill them all (eg volcanic eruption) ▼ Resistant Bacteria ▾ How do bacteria evolve? evolves rapidly because they reproduce at a fast rate ▾ How does antibiotic resistance occur? 1. a population of bacteria enters the body 2. it goes through mutations causing a part of the bacteria to become antibiotic resistant (by chance) 3. the person consumes antibiotics and all die except for the resistant bacteria 4. this strain survives and reproduces 5. it spreads to other people - there is no treatment and nobody is immune ▼ What is one example of an antibiotic-resistant strain of bacteria? MRSA ▾ How do you reduce the rate of antibiotic resistance? doctors should not prescribe antibiotics inappropriately - eg treating non- serious or viral infections ● • patients should complete their course of antibiotics so all bacteria are killed • agricultural use of antibiotics should be restricted ▼ Why don't doctors create new anti-biotics to defeat these strains? expensive and time-consuming strains like these appear often - difficult for doctors to keep up 4.6.4 Classification of Living Organisms ▾ Which system were organisms classified into? Unit 6 - Inheritance, Variation and Evolution 15 the Linneaen System - proposed by Carl Linnaeus ▼ What were the organisms divided into? kingdom - phylum - class - order - family - genus - species ▼ Why did classification systems change over time? evidence of internal structures became more developed due to improvements in microscopes and the understanding of biochemical processes progressed ▼ What was the three-domain system? organisms are divided into: ▼ archaea primitive bacteria usually living in extreme environments ▼ bacteria true bacteria ▼ eukaryota includes protists, fungi, plants and animals What was the binomial system? how organisms are named - given a two-part latin name the first part = the genus the second part = the species What are evolutionary trees? a method used by scientists to show how they believe organisms are related ▾ How do scientists make evolutionary trees? They use current classification data for living organisms and fossil data for extinct organisms. 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