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1 REVISION NOTES: SUMMARY OF B1 TOPIC 1: Classification and genetics. Go through your revision tracker so far I can do this very well: I think I can remember this even without revision I can do this quite well: I think I get this but I need to revise it to remember it I need more work on this: I don t get this at all even if I revise it I don t think I get it.

2 Classification 1.1 Describe how biologists classify living organisms according to how closely they are related to one another including: a Species b Genus c Family d Order e Class f Phylum g The Five Kingdoms As you go down the levels the organisms will have more in common and will be more closely related.

3 Animal cell and Plant cell cell nucleus cell Cell wall Cell membrane Starch grain Cytoplasm Cytoplasm Chloroplast Vacuole nucleus Plant cells have chloroplasts (containing chlorphyll) and animal cells don t. Plant cells have a cell wall animal cells don t.

4 Cell Parts you need to know Nucleus controls the cell and contains DNA. (Same for both plant and animal cells). Cell wall gives strength and support to plant cells. Chloroplasts contain chlorophyll which absorbs light for photosynthesis so the plant cell can make glucose.

5 Kingdoms (See next slide) 1.2 Describe the main characteristics of the five kingdoms including a Animalia b Plantae c Fungi d Protoctista e Prokaryotae 1.2 Describe the main characteristics of the five kingdoms including a Animalia are multi celled, have cells with a nucleus but no cell wall or chlorophyll. They feed heterotrophically. b Plantae - are multi celled, have cells with a nucleus, also have a cell wall and chlorophyll. They feed autotrophically. c Fungi - are multi celled, have cells with a nucleus and cell wall but no chlorophyll. They feed saprophytically. d Protoctista single celled and have a nucleus. e Prokaryotae single celled and have no nucleus.

6 Kingdom: Animalia Kingdom: Plantae Kingdom: Fungi Kingdom: Protoctista Kingdom: Prokaryotae Multi-celled Multicelled Multicelled Single (uni) celled Single (uni) celled Have nucleus Have nucleus Have nucleus Have nucleus No nucleus Have no cell wall, no chlorophyll Have cell walls, have chlorophyll Have cell walls, do not have chlorophyll, Example: euglena Example: bacteria Eat other organisms (feed heterotrophically) Examples: Fish, human Use light from the sun to make own food (feed autotrophically) Examples: trees, flowers, Absorb nutrients from other organisms or dead and decaying matter (feed saprophytically) Example: mushrooms,

7 Euglena Euglena Euglena is difficult to classify as it has features of several kingdoms. It has chloroplasts and so can feed autotrophically, which puts it in the plantae kingdom. It has a gullet to take in food which puts it in Animalia. It can move using a flagellum putting it in the Animlia kingdom. However, it is unicellular (single-celled) and has a nucleus. Therefore it is placed in the Protoctista kingdom. It cannot be placed in prokaryotae as this kingdom has no nucleus. Grade It cannot E: Can be you Prokaryotae recall the Grade as Prokaryotae D: do Grade not C: have Can you a nucleus discuss the and main Euglena features does. of all of names of the kingdoms and give examples of each. Can you explain the cell features of each kingdom. the kingdoms. Grade B Extension: Classify euglena and justify your decision.

8 Viruses 1.3 Explain why scientists do not classify viruses in any of the five kingdoms and regard them as non-living. The kingdoms consist of all the living organisms. Viruses are not classified into any of the 5 kingdoms because viruses are non-living and the kingdoms only contain living organisms. Viruses are classed as non-living because they do not fulfil all of the 7 life processes. They can only reproduce. They take over a host cell, injecting its DNA which makes the cell make multiple copies of the virus. The viruses then explode out of the cell, destroying it, and then go to destroy other cells.

9 Vertebrates 1.5 Explain how scientists place vertebrates into groups based on a oxygen absorption methods lungs, gills and skin b reproduction internal or external fertilisation, oviparous or viviparous c thermoregulation homeotherms and poikilotherms d body covering fur / hair, feathers, dry scales, moist skin, and wet scales.

10 Ready to learn starter: Recall the 5 groups of vertebrates. Mammals, birds, reptiles, amphibians, fish. What do all vertebrates have in common? They all have a backbone (supporting rod running the length of the body) What phylum do all vertebrates (including humans belong to?) Chordata (have spinal cord) Then give the characteristics of each vertebrate group. Mammals use internal fertilisation and are viviparous. They are homeothermic, have fur and obtain oxygen using lungs. Birds use internal fertilisation and are oviparous. They are homeothermic, have feathers and obtain oxygen using lungs. Reptiles use internal fertilisation and are oviparous. They are poikilothermic, have dry scales and obtain oxygen using lungs. Amphibians use external fertilisation and are oviparous. They are poikilothermic, have moist skin and obtain oxygen using gills, lungs and through their skin. Fish use external fertilisation and are oviparous. They are poikilothermic, have wet scales and obtain oxygen using gills.

11 Features Reproduction methods Thermoregulation Body covering Oxygen absorption method Mammals Internal fertilisation Give birth to live young (Viviparous) and feed milk to them Warm blooded (Homeotherms) Constant body temperature Have hair or fur Have lungs to breathe Birds Internal fertilisation Lay eggs (Oviparous) Warm blooded (Homeotherms) Constant body temperature Have feathers Have lungs to breathe Reptiles Internal fertilisation Lay eggs (Oviparous) Cold blooded (Poikilotherms) Body temperature varies with the temperature of its surroundings Have dry scales Have lungs to breathe Amphibians External Fertilisation Lay eggs (Oviparous) Cold blooded (Poikilotherms) Body temperature varies with the temperature of its surroundings Have moist, soft skin Gills when young Lungs when adults Also absorb oxygen through their skin Fish External fertilisation Lay eggs (Oviparous) Cold blooded (Poikilotherms) Body temperature varies with the temperature of its surroundings Have wet scales Have gills to take in oxygen from the water

12 One of the phyla of the Animalia Kingdom is: The Chordata is the animal phylum that includes humans and other vertebrates. (Note: not all chordates are vertebrates) Kingdom: Animalia Phylum: Chordata

13 1.3 Describe that all vertebrates have a spinal cord and therefore are chordates. 1.4 Describe the main characteristics of the phylum chordata as animals with a supporting rod running the length of the body, an example of this being the backbone in vertebrates. Chordate features Chordates have these features at some point in their life supporting rod (or backbone) - running the length of the body, an example of this being the backbone in vertebrates. The job of the backbone is to protect the spinal cord. Spinal cord - a bundle of nerves which runs down the "back".

14 Difficult keywords oviparous viviparous Lays eggs Gives birth to live young homeotherms Internal fertilisation External fertilisation Constant body temperature animal can regulate its own body temp poikilotherms Body temperature varies with its surroundings animal cannot regulate its own body temp Egg and sperm meet inside the female body animals have sex Egg and sperm meet outside the female body usually in water ALL: Identify the 5 groups of vertebrates and give 1 feature for each group (Grade E) MOST: Establish the main features of the 5 groups of vertebrates. Explain the words: oviparous, viviparous, homeotherm, poikilotherm (Grade D) SOME: Discuss how scientists classify vertebrates? (Grade C)

15 1.6 Outline the problems with classifying vertebrates to a specific group based on their characteristics and why many vertebrates are difficult to classify. Axolotl Difficult to classify because it has features of fish and amphibians. It has gills as adults and spends all its time in water. Poikilothermic (fish features). Has limbs and can walk, has smooth moist skin, poikilothermic (amphibian features).

16 1.6 Outline the problems with classifying vertebrates to a specific group based on their characteristics and why many vertebrates are difficult to classify. Platypus The platypus is the only mammal that lays eggs which are leathery like reptile eggs. They also have a skeleton like a reptile. They have fur and are homeotherms like mammals. They have a beak and webbed feet like birds. Have features of more than one vertebrate group.

17 Eg A lion and tiger interbreed to have a liger. Definition of hybrid The animals in the pictures are all called HYBRIDS They are the offspring from two different species interbreeding. They are neither species; they show characteristics of both parents.

18 1.7 Discuss why the definition of a species as organisms that produce fertile offspring may have limitations: a some organisms do not always reproduce sexually (bacteria do not interbreed they simply divide) and b sometimes different species do interbreed to produce hybrids and some are fertile (eg mallard ducks) Definition of a species A species is a group of organisms that: can interbreed (reproduce with one another) and produce offspring that are fertile (able to reproduce)

19 Three Limitations of a definition of a species. 1. Occasionally different species do interbreed to produce hybrids 2. Some organisms do not always reproduce sexually (bacteria do not interbreed they simply divide) and some plants make copies of themselves. 3. Sometimes different species do interbreed to produce hybrids and some are fertile (eg mallard ducks)

20 Binomial classification 1.8 Know how to write a binomial name and what levels of classification each name refers to. Binomial names are the Genus and species of the organism.

21 Genus species Homo sapien (wise human) Capital letter Lower case letter This is called the binomial system all species are given a two part Latin name. Rules: First part of the name refers to the Genus Always starts with a capital letter. Second part of the name refers to the species Always starts with a lower case letter. Full name in italics. ALL: Give 3 examples of hybrids. (Grade E) MOST: Correctly identify and write binomial names. (Grade D) SOME: Define the terms species and hybrid and suggest why these definitions may be limited. (Grade C) FEW: Discuss why classification can be made complicated by hybrids (Grade B)

22 Polar bear correct binomial name Ursus maritimus First word genus starts with a capital letter, Second species word is all lower case. All in italics.

23 Binomial names If two different organisms have the same first name (belong to the same Genus), it means they are closely related. Panthera tigris Panthera leo (common name = tiger) (common name = lion) Both these organisms belong to the same genus and so are closely related

24 Sample exam question: The binomial name for a house sparrow is Passer domesticus. Draw two lines to correctly match the genus and species of the house sparrow with its binomial name. genus species Passer sparrow domesticus

25 Why is binomial classification useful? H 1.8 Explain why binomial classification is needed to identify, study and conserve species, and can be used to target conservation efforts The binomial classification is useful to when naming robins because America and England use the same word (robin) for two different birds that are not the same species. See below. The system is useful as it allows scientists to communicate clearly what species they are talking about (avoids confusion). Binomial classification is useful as it allows scientists to easily identify existing and new species. They can also use it to see how closely organisms are related if different organisms share the same first name, they belong to the same genus and are closely related. American Robin Turdus migratorius English Robin Erithacus rubecula

26 HIGHER STUFF Why is binomial classification useful? They can also use the binomial system to identify areas in the world that have greater and lesser biodiversity. Biodiversity is the number of different species of organisms in a specific area. (Lots of different organisms = great biodiversity / very few different organisms = lesser biodiversity). You need to use binomial classification to identify the different species in an area to give a measure of biodiversity. You can then communicate ideas to scientists over the world about which areas of the world need conserving. If we did not use the binomial system, these organisms would not be as easily identified and areas of the world may not be conserved meaning species may go extinct. Biodiversity is important because we rely on living things for food, medicines and many other products. The more species there are in the world the more possible products available to us (a possible cure for cancer). If we do not use binomial system, we may not conserve the correct places and these products will not be available to us. The binomial system is important in these types of conservation projects as it can be used to identify and study the species at threat, deciding which need to be conserved, and then putting the conservation into place. This should help species to survive and not go extinct. If it is used to help conserve areas such as the Tropical Andes then eventually we may discover more and more species and get different cures for diseases etc.

27 1.9 Explain how accurate classification may be complicated by: a variation within a species Sometimes organisms of the same species look very different but are the same species (eg humans, dogs). Sometimes different species look exactly alike but are different species (meadowlark).

28 HIGHER STUFF: Why is classification of organisms sometimes difficult. 1.9 Explain how accurate classification may be complicated by: H H b hybridisation in ducks H c ring species

29 HIGHER STUFF: b. Hybridisation in Mallard ducks Hybridisation (where two similar species interbreed to produce a hybrid). Mallard ducks can hybridise with other closely related species of duck to produce fertile hybrid duck offspring. These hybrid offspring then breed with other hybrids, Mallards or other duck species producing ducks with a continuous range of characteristics, rather than separate species. This makes classification of them difficult.

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31 HIGHER STUFF: c. Ring species The Larus gulls interbreed in a ring around the arctic. Ring species as shown below is where populations of the same species can interbreed with neighbouring populations. For instance the Larus gulls at number 4 may interbreed with the neighbouring populations at number 3 and 5. However the two populations at the ends (1 and 7) cannot interbreed. It is hard to divide ring species into separate species which sometimes makes classification difficult.

32 Ready to learn starter: A scientist has discovered something new. How can this discovery be validated?

33 1.19 Explain the role of the scientific community in validating new evidence, including the use of: a scientific journals b the peer review process c scientific conferences Validating new evidence If a scientist discovers something new how can we believe them? They will: Write a paper detailing their method and results. This will then be peer reviewed (other scientists assess it to see if it is any good). It may then be published in a scientific journal if it is good enough. He may discuss his study and results at a scientific conference. Other scientists may then decide to repeat the study to see if they find the same thing.

34 1.10 Construct and use keys to show how species can be identified Using keys to identify organisms This is a branching key

35 Grade C: Can you use yes / no keys to identify organisms Grade B: Can you Establish how to use yes / no and statement keys to identify organisms Grade A A*: Can you Design a simple key to identify 8 organisms

36 Ready to learn starter: Variation questions What is variation? What are the two types of variation and give examples. What are the causes of the two types of variation? What kinds of graphs show each type of variation?

37 1.13 Describe variation as continuous or discontinuous We call the differences between organisms The two types of variation are : Continuous and Discontinuous variation Continuous variation = can be a range of values or measurements eg height, weight Discontinuous variation = Fits into certain categories eg blood group, hair colour, shoe size. ALL: State what is meant by variation, and (Grade E) conduct an investigation into variation. (SKILL) Describe variation as continuous or discontinuous and give examples. (Grade D) MOST: Establish what causes variation within species. (Grade C) SOME: Interpret variation graphs using normal distribution curves (Grade B) FEW: Perform calculations based on graph information (Grade A-A*)

38 Continuous / Discontinuous variation Continuous variation = can be a range of values or measurements eg height and weight Discontinuous variation = Fits into certain categories eg blood group, gender, eye colour ALL: State what is meant by variation, and (Grade E) conduct an investigation into variation. (SKILL) Describe variation as continuous or discontinuous and give examples. (Grade D) MOST: Establish what causes variation within species. (Grade C) SOME: Interpret variation graphs using normal distribution curves (Grade B) FEW: Perform calculations based on graph information (Grade A-A*)

39 Variation is caused by : What causes variation? 1. Discontinuous variation is are inherited variation. Features passed on from parents sexually reproducing and passing on genes. Features obtained by mutation a change in the DNA. 2. Continuous variation is caused by a combination of genes and environment. This means features that are affected by the surroundings. For example, height and weight are both genetic and affected by your diet / illness. ALL: State what is meant by variation, and (Grade E) conduct an investigation into variation. (SKILL) Describe variation as continuous or discontinuous and give examples. (Grade D) MOST: Establish what causes variation within species. (Grade C) SOME: Interpret variation graphs using normal distribution curves (Grade B) FEW: Perform calculations based on graph information (Grade A-A*)

40 1.16 Describe the causes of variation, including: a genetic variation different characteristics as a result of mutation or reproduction b environmental variation different characteristics caused by an organism s environment (acquired characteristics) next

41 1.15 Interpret variation graphs using normal distribution curves Continuous variation This graph shows a normal distribution graph (bell shaped curve). It shows continuous variation such as height or weight. Continuous variation is caused by a mixture of genes and the environment and are known as acquired characteristics. Most people fall into the centre of the graph. Very few people fall at the extreme ends.

42 Discontinous variation Goes into categories will show a bar chart with no particular pattern. This graph shows discontinuous variation which is caused by genes (parents sexually reproducing or a mutation a change in the DNA).

43 1.11 Explain how organisms are adapted to their environment and how some organisms have characteristics that enable them to survive in extreme environments, including deep-sea hydrothermal vents and polar regions Adaptations!!! Adaptations are features that help an organism survive in its environment!

44 Extreme environments Arctic vs Hydrothermal vents Extremely cold Slippery ice Extremely Hot Very little or no light so no photosynthesis Lots of snow Temperature can be -40 degrees High pressure Acidic environment and toxic hydrogen sulphide

45 Large feet which enables them to Small ears to Thick layer of blubber under skin for Black skin to White fur for Rough pads on feet to Thick fur for Polar bear spread weight to stop them sinking in the snow also for swimming conserve heat insulation and energy reserves absorb heat camouflage grip the ice. insulation Pompeii Worm Shell or tough body that is adapted to high pressures No eyes to conserve energy (doesn t need them, it s too dark.) Sensitive tentacles to sense the environment Spends a lot of time in a hide from predators tube to Body covered in thick layer protect it from the heat of bacteria to

46 Tube worm This is different to a pompeii worm. Tubeworms have bacteria that live inside them that convert hydrogen sulphide compounds (from the vents) into food for the tube worms. In return the tubeworm provides oxygen / protection for the bacteria. This is an example of mutualism. (mutualism is the way two organisms exist in a relationship in which each benefits) ALL: Can you give examples of extreme environments and outline why they are extreme. (Grade C) MOST: Establish the adaptations of a polar bear and pompeii worm. (Grade B) FEW: Can you explain in detail how the adaptations of a polar bear and pompeii worm allow them to live in these environments. (Grade A) FEWER: Consider how tube worms feed by chemosynthesis and how bacteria assist with this, and how this is an example of mutualism. (Grade A*)

47 Evolution 1.12 Demonstrate an understanding of Darwin s theory of evolution by natural selection including a variation b over-production c struggle for existence d survival of the fittest (natural selection) e advantageous characteristics inherited f gradual change (evolution)

48 The 6 main stages of evolution. 1. An animal may have lots of babies (over production) 2. These will all be different (variation) 3. There will be competition for survival (food, water, shelter, escape from predator). 4. The weaker or less adapted ones die whilst the ones that have the best characteristics will survive. (Survival of the fittest or natural selection) 5. These will breed and pass on the genes for these characteristics. 6. This leads to a gradual change in the species over time (evolution)

49 Hedgehog example Example: How the hedgehog got its spines Several million years ago a species of mammal had long, thick hair. However, some of the mammals had soft hairs and some had stiffer hair than others (variation) The mammal had about 6 pups at a time (overproduction). More pups meant competition for survival. (For space, water, food or escape from predators). A new predator entered the area in which the mammal lived. The predator avoided eating the mammals with the stiffer hair and ate more of the ones with softer hair. (Competition for survival). So, the mammals with softer hair died out. The ones with the stiffer hair survived. The ones with the stiffer hair had the good feature that helped it to survive (it was the best adapted). (Survival of the fittest or natural selection). These were able to breed and pass this characteristic onto their offspring. (Breeding and passing on genes). Over thousands of years, the mammals with the stiffest hairs were the most likely to survive and gradually this became a species of mammals with spines. The hedgehog. (Evolution or gradual change).

50 EXTINCTION 1. Sudden change in an organisms environment (This may be due to climate change, lack of food, a new predator, loss of habitat). 2. None of them have adaptations to help them survive. 3. They start to die they may all go extinct.

51 Ready to learn starter: Can you recall and explain the evidence for Darwin? There are 5 main pieces of evidence for Darwin s Theory of evolution by natural selection. These are: Fossil Record DNA evidence Peppered moth Resistant rats Speciation Can you summarise each piece of evidence and explain how it supports Darwins theory?

52 Evidence for Darwin 1.18 Explain how evidence from DNA research and the emergence of resistant organisms support Darwin s theory. Evidence for Darwin includes: Peppered Moth: Before the industrial revolution the pale moth was camouflaged and so there were lots of these. There were very few dark moths which were not camouflaged and got eaten by birds. After the industrial revolution lots of smoke went on the trees, camouflaging the dark moths and showing up the pale moths which started getting eaten more. The dark moths survived, bred and passed on their gene for the dark wings to their offspring. Over time the numbers of dark moths increased and the numbers of pale moths decreased. Resistant rats and bacteria: A mutation has led to a rat being resistant to rat poison (warfarin). Warfarin will kill the non-resistant rats. The resistant rats survive, pass on the resistant gene to their offspring. Over time the numbers of warfarin resistant rats go up, the numbers of non-resistant rats go down (and will possibly become extinct one day). DNA evidence: All living things on our planet use DNA as their instruction manual. This suggests all life is related, just as we expect from Darwin s theory. When you do this you can compare the DNA of lots of different living creatures. Amazingly, you find some of the same chunks of DNA in bacteria as in humans. Speciation : The formation of two different species from one original species. Eg the finches on the Galapagos islands. Originally the finches on two different islands were the same species, but all showed variation in their beak size (some had fatter beaks and some had thin beaks). On one island there were lots of nuts. The fat beaked bird survived as they could crack and eat the nuts. They could then breed and pass on the fat beak gene to their offspring. Thin beaked birds died. Over time all birds on this island had fat beaks. On the other island there were lots of insects. The thin pointy beaked bird survived as they could get in the holes to eat the insects. They could then breed and pass on the thin beak gene to their offspring. Fat beaked birds died as they could not get the insects. Over time all birds on this island had thin beaks. Eventually the birds on each island become so different that they will become two separate species (speciation) and will not interbreed. Fossil Record: The fossils discovered show slight changes in species over time, supporting Darwin.

53 Genes where are they? 1.20 Describe the structure of the nucleus of the cell as containing chromosomes, on which genes are located 1.21 Demonstrate an understanding that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics Genes are on the chromosomes. Chromosomes are found in the nucleus of a cell as shown on the next slide.

54 Nucleus Cytoplasm Cell membrane Chromosomes in nucleus Full set f 23 pairs of chromosomes Gene 1 chromosome A strand of DNA Base pairs

55 Can you summarise what each part does and give the order do they go in from largest to smallest The three main parts of an animal cell are cell membrane, cytoplasm and nucleus. In the nucleus of each cell there are 46 chromosomes 23 pairs. 23 inherited from mum, 23 inherited from dad. Each chromosome sometimes looks like an X shape it is thread like and made up of coiled DNA and divided into many genes. A gene is a section or strand of DNA that contains instructions for making a specific protein. This protein may be for hair colour etc. DNA is made up of 4 different bases that form the unique code that makes you you! Grade E Can you state where the genetic information is found in a cell. Grade D Can you label a diagram (model) of the structures that are involved in inheritance. Grade C Can you label a diagram (model) of the structures that are involved in inheritance and make use of the information to summarise each part. Grade B Can you determine how the structures link together. HOT

56 Ready to learn starter: Can you define the following genetics keywords. Gene Allele Genotype Phenotype Homozygous Heterozygous Dominant Recessive

57 Genetics words 1.22 Recall the meaning of, and use appropriately, the terms: dominant, recessive, homozygous, heterozygous, phenotype and genotype Gene Allele Genotype Phenotype Strand of DNA. Codes for a protein that may give you your eye or hair colour. A different or alternative version of the same gene. The alleles you actually have for a characteristic. Physical characteristics Homozygous Matching alleles e.g. HH or hh Heterozygous Dominant Recessive Different alleles, e.g. Hh. An allele represented by a capital letter. Even if you only have one of these, you will have this characteristic. An allele represented by a lower case letter. You need both of these alleles to have this characteristic.

58 Different versions of genes Here the gene that is shown codes for petal colour it is the same gene. gene for petal colour version for red petals gene for petal colour version for yellow petals Each chromosome may have a different version of a gene. Different (or alternative) versions of a gene are called alleles.

59 Inheritance Therefore sperm have 23 chromosomes which fuse with 23 chromosomes in the egg at fertilisation so that the fertilised egg has 46 chromosomes the normal amount for a human.

60 Punnet squares probabilities, percentages and ratios 1.23 Analyse and interpret patterns of monohybrid inheritance using a genetic diagram and Punnett squares 1.24 Calculate and analyse outcomes (using probabilities, ratios and percentages) from monohybrid crosses

61 Ready to learn starter: Normal = F Cystic fibrosis = f Ff Ff Complete the punnet square correctly. Then give the probability that these people could have a cystic fibrosis child. What percentage of their children could be carriers of the cystic fibrosis allele? What is the ratio of normal to cystic fibrosis children?

62 Tallness T = tall t = short T T T t T TT Tt T TT Tt T t Probability = number out of four. So will be either 0/4 ; 1/4 ; 2/4; 3/4 or 4/4 The probability of having a tall child is 4/4

63 Tallness T = tall t = short T T T t T TT Tt T TT Tt T t Percentage = number out of hundred. So will be either 0% ; 25% ; 50%; 75% or 100% The percentage of tall children is 100%

64 Tallness T = tall t = short T T T t T TT Tt T TT Tt T t Ratio = number that have the trait compared with them that dont. 4:0 ; 3:1 ; 2:2 ; 1:3 ; 0:4. (Will always add up to four!) The ratio of tall children to short children is 4:0

65 1. Explain why both of the parents had brown eyes. 2. Were the parents heterozygous or homozygous? 3. Explain why the two brown eyed parents have been able to produce a blue eyed child. Use a punnet square to help with your explanation If one of the parents was homozygous dominant for brown eyes, explain whether they could produce blue-eyed offspring. Keywords: heterozygous homozygous dominant recessive offspring alleles gene offspring See next slide

66 Model answer to previous slides questions 1. Both parents have brown eyes as they must have at least 1 dominant gene each for brown eyes. 2. The parents must be heterozygous (Bb) because they have got a blue eyed child, so both parents must have a recessive blue eyed allele to pass down to the blue eyed child as you need two recessive alleles to be blue eyed. 3. The brown eyed parents are carriers of the blue eyed allele. You can only be blue eyed if you inherit two recessive alleles from your parents, therefore each parent has passed down this allele to the blue eyed baby. A punnet square to show this would be: B B BB Bb b Bb bb b Blue eyed baby 4. If a parent was homozygous dominant their genotype would be BB. They would only be able to pass a dominant gene to their offspring, so therefore all offspring would have brown eyes, as they would inherit at least one dominant allele. B B B BB BB b Bb Bb All brown eyed

67 Ready to learn starter: What are the three main symptoms of cystic fibrosis? Can you explain why these symptoms occur?

68 Genetic disorders 1.25 Describe (and explain) the symptoms of the genetic disorders: a sickle cell disease b cystic fibrosis

69 Ready to learn starter: What are the three main symptoms of sickle cell disease? Can you explain why these symptoms occur?

70 Sickle Cell Disease Symptoms Breathlessness Pain (called crisis) Tiredness This happens because... sickle blood cells block blood vessels in the lungs. This happens because... Sickle-shaped blood cells stick together and can block blood vessels (called a crisis and normally in joints) This happens because... sickle blood cells cannot carry as much oxygen to cells, leading to less respiration and so less energy. ALL: Outline some symptoms of cystic fibrosis and sickle cell disease. (Grade D) MOST: Establish why the symptoms of cystic fibrosis and sickle cell disease happen.(grade C) SOME: Solve, analyse and interpret punnet square and family pedigree diagram problems (Grade B)

71 HIGHER STUFF: Pedigree Analysis: What is it? This is where doctors may study family pedigree charts to assess the probability that a couple may pass on (or may have already passed on) a genetic disorder to their child. Basic Symbols ALL: Outline some symptoms of cystic fibrosis and sickle cell disease. (Grade D) MOST: Establish why the symptoms of cystic fibrosis and sickle cell disease happen.(grade C) SOME: Solve, analyse and interpret punnet square and family pedigree diagram problems (Grade B)

72 More Symbols ALL: Outline some symptoms of cystic fibrosis and sickle cell disease. (Grade D) MOST: Establish why the symptoms of cystic fibrosis and sickle cell disease happen.(grade C) SOME: Solve, analyse and interpret punnet square and family pedigree diagram problems (Grade B)

73 What does this show (see next slide)

74 This shows that Richard and Diane who are a couple, have had two children (Michael and Brian). Brian has cystic fibrosis but both his parents are normal (as they both have a dominant normal allele). His parents are both carriers of the cystic fibrosis allele, and both have passed this down to Brian. Sam has a 50% chance of having cystic fibrosis because his mum is a carrier of the allele. C c Cc cc c Cc cc c 2/4 will have cystic fibrosis This is 50% 2:2 (For every 2 normal children there will be 2 cystic fibrosis children.

75 HIGHER STUFF: Pedigree Analysis why do it? H 1.26 Evaluate the outcomes of pedigree analysis when screening for genetic disorders: a sickle cell disease b cystic fibrosis