1. 1. Y E A R 1 0 M S G I B E L L I N I Genetics
2. 2. Student Learning Objectives Explain how variation assists in species survival Distinguish between continuous and discrete variation Explain sex chromosomes Distinguish between dominant and recessive alleles Explain the terms genotype, phenotype, homozygous and heterozygous Draw and use punnet squares Describe what a pedigree is Describe DNA and genes Explain the genetic code Explain what a mutation is
3. 3. SLO Explain how variation assists in species survival Distinguish between continuous and discrete variation
4. 4. Uniquely you The population of the Earth is more than 6 billion people, and no two individuals (apart from identical twins) are genetically the same. Why? People are different because they inherit different characteristics (or traits) from their parents. Like all babies, this child carries a unique set of genes; half from his mother and half from his father. A persons unique characteristics are caused by: the set of genes they inherited from their parents (nature) the environment in which they developed (nurture).
5. 5. Inherited and acquired characteristics Differences in some characteristics are due to a combination of both inherited and environmental factors. In some cases, it can be difficult to say how much influence each factor has. Other types of characteristics, such as scars and hair length, are not inherited but depend on environmental factors. These are called acquired characteristics. Some characteristics, such as eye colour and earlobe shape, are only determined by genes. These are called inherited characteristics.
6. 6. Nature, nurture or both?
7. 7. Variation Variation occurs when individuals within a population differ Selection of those best suited to the environment leads to a change in the make up of a population over time and the evolution of new species
8. 8. Inheritance Why do we look the way we do? You inherit traits (features) from your parents These traits are passed to you in your chromosomes Organisms must have variety within populations in order to survive change.
9. 9. Phenotype and genotype The overall appearance of an organism depends on two things: The full set of genes of an organism is called its genotype. All the observable characteristics of an organism are called its phenotype. 1. its genes (inherited characteristics) 2. the effects of the environment in which it lives. An organisms phenotype therefore depends on its genotype plus environmental effects. phenotype = genotype + environmental effects
10. 10. Classifying variation Characteristics can be classified in different ways. How would you categorize variation in eye colour? Could height be categorized in the same way? A feature that can be measured and given a value from a range of values shows continuous variation. A feature that cannot be measured but is one of a few distinct options shows discontinuous variation. Which type of variation are eye colour and height?
11. 11. Variation There are two types of variation Continuous range eg height Discontinuous either or, you have it or you dont, eg tongue roller
12. 12. Discontinuous Variation Characteristic Yes No A B Male Female Widows peak Straight edge Free ear lobe Attached ear lobe Straight thumb Hitch hikers thumb Tongue roller Non tongue roller
13. 13. Variation Graph What shape is your graph? Not quite a bell shape If your graph does not show a bell shaped curve why not? Because sample size is too small What is the biological importance of variation? To survive environmental change
14. 14. What type of variation?
15. 15. Variation http://www.youtube.com/watch?v=oWP3nWe-4K8 Complete Dinosaur Variation Worksheet Complete page 48 Year 10 Science Workbook
16. 16. Success Criteria Why is it important for populations to have variation? Where do we get our inherited characteristics from? Give two examples of inherited characteristics Why dont we look exactly like our parents?
17. 17. Success Criteria Why is it important for populations to have variation? So that they can survive environmental changes Where do we get our inherited characteristics from? Parents, parents parents, parents parents parents Give two examples of inherited characteristics Nose shape, eye colour, hair colour Why dont we look exactly like our parents? Because we are a mixture of mum and dad, and the environment
18. 18. SLO Describe DNA and genes Explain the genetic code
19. 19. Genetics the basics
20. 20. Alleles, genes and chromosomes Alleles alternative form of a gene eg blue eyes (b) or brown eyes (B) Gene section of DNA that codes for a characteristic eg eye colour Chromosome coiled length of DNA (deoxyribose nucleic acid)
21. 21. Karyotype
22. 22. Karyotype Chromosomes are matched up into Homologous Pairs (same chromosome, one from each parent) Homologous pairs of chromosomes are then ordered from longest to smallest. Sex chromosomes always go at the bottom right In humans we have 22 pairs of body cells and two sex cells total of 46 chromosomes
23. 23. Chromosome Numbers Body cells have 23 pairs or 46 chromosomes Egg and sperm must have half or one set of chromosomes so that when they join to make a new child, that child only has 46 chromosomes (not 92!)
24. 24. Success Criteria Where are chromosomes found? In the nucleus of all cells What is a gene? Section of DNA that codes for a characteristic eg eye colour Where do we get our inherited characteristics from? Our parents How many chromosomes do we have? 46
25. 25. SLO Explain what a mutation is
26. 26. Mutations Mutations are a permanent change in the base sequence of DNA Mutations are the ultimate source of variation as they give rise to NEW phenotypes
27. 27. Mutagens Mutations (changes in base sequence of DNA are caused by: UV A rays Radio waves Some chemicals Heavy metals Problems during meiosis or DNA replication
28. 28. True or false?
29. 29. Family resemblanceMembers of the same family often look similar. If the son and daughter have children of their own one day, will they also look like their parents? Which parent do these children look more like? Humans, like all organisms, inherit characteristics from their parents. How are characteristics passed on? Why do members of the same family look similar?
30. 30. Different versions of genesChromosomes in a homologous pair contain the same type of genes that code for the same characteristics, such as eye colour. Each different version of a gene is called an allele. Each chromosome in the pair, however, may have a different version of the gene. For example, the version of a gene on one chromosome may code for brown eyes, whereas the version of the gene on the other chromosome may code for blue eyes. allele for brown eyes allele for blue eyes
31. 31. Homozygous allelesIf the alleles for a characteristic in a homologous pair are the same, the organism is said to be homozygous for that characteristic. What colour eyes will these homozygous pairs of alleles produce? allele for brown eyes allele for brown eyes allele for blue eyes allele for blue eyes
32. 32. Heterozygous alleles The characteristic expressed by heterozygous alleles will depend on which allele is dominant and which allele is recessive. If the alleles for a characteristic in a homologous pair are different, the organism is said to be heterozygous for that characteristic. What colour eyes will this heterozygous pair of alleles produce? allele for brown eyes allele for blue eyes ?
33. 33. Dominant or recessive? Dominant alleles are always expressed in a cells phenotype. Only one copy of the dominant allele needs to be inherited in order for it to be expressed. Dominant alleles (e.g. brown eyes) are represented by an upper case letter (e.g. B). The phenotype for a particular characteristic depends on which allele is dominant and which allele is recessive. Recessive alleles are only expressed in a cells phenotype if two copies of it are present. If only one copy is present, its effect is masked by the dominant allele. Recessive alleles (e.g. blue eyes) are represented by a lower case letter (e.g. b).
34. 34. What eye colour? The allele for brown eyes is dominant over the allele for blue eyes. The individual will have brown eyes, because the allele for brown eyes masks the allele for blue eyes. allele for brown eyes allele for blue eyes So, what colour will the eyes be of an individual who is heterozygous for eye colour?
35. 35. Inheritance terms
36. 36. SLO Distinguish between dominant and recessive alleles Explain the terms genotype, phenotype, homozygous and heterozygous
37. 37. Terms;Terms;Terms;Terms Term Definition Phenotype Physical characteristic, blue eyes Genotype Letters representing alleles, Bb Homozygous Same letters (alleles) BB, bb Heterozygous Different letters (alleles) Bb Alleles Alternative form of a gene Dominant Always expressed if present, capital letter, B Recessive Requires two alleles to be present to be expressed, lower case letter, b Pure breeding Homozygous for the desired trait
38. 38. Homozygous cross
39. 39. Heterozygous cross
40. 40. Finding the genotypeFor some characteristics, the genotype of a homozygous recessive individual can be determined from their phenotype. A test cross can be used to determine whether an individual is homozygous or heterozygous for a dominant trait. But what about individuals that have brown fur? Is their genotype BB or Bw ? For example, the allele for brown fur (B) in mice is dominant over the allele for white fur (w). This means that all white mice must therefore have the genotype .
41. 41. What is a test cross?During a test cross, an individual with an unknown genotype is crossed with a homozygous recessive individual. The phenotype of the offspring will reveal the unknown genotype. If all the offspring display the dominant phenotype, then the parent of unknown genotype must be homozygous for the characteristic. If half the offspring show the dominant phenotype, and half show the recessive phenotype, then the parent must be heterozygous for the characteristic.
42. 42. Using test crosses to find genotype
43. 43. Mendels experimentsOver seven years, Mendel experimented on more than 28,000 pea plants! Why were his experiments so successful? Pea plants grow quickly. Pea plants are available in pure- breeding (homozygous) strains. Many pea plant characteristics show discontinuous variation; they are either one form or another, with no intermediates. This means that their phenotypes are easily distinguishable.
44. 44. Mendels early experiments
45. 45. Monohybrid crosses There are two alleles controlling pea shape. This means there are three possible genotypes that the F2 generation of plants could inherit, leading to two possible phenotypes. SS ww Sw smooth wrinkly smooth Genotype heterozygous homozygous dominant homozygous recessive Phenotype The type of experiment that Mendel carried out, investigating just a single characteristic, is called a monohybrid cross. The likelihood of a trait being produced during a monohybrid cross can be mapped out using a Punnett Square.
46. 46. What are Punnett Squares?
47. 47. Mendels laws of inheritanceAfter his research, Mendel proposed two laws of inheritance. Mendels first law: the law of segregation Mendels second law: the law of independent assortment Alternate versions of genes (alleles) cause variation in inherited characteristics. An organism inherits two alleles for each characteristic one from each parent. Dominant alleles will always mask recessive alleles. The two alleles for each characteristic separate during gamete production. Genes for different characteristics are sorted independently during gamete production.
48. 48. Predicting Offspring Parent Phenotype: Brown x Brown Parent Genotype: Bb x Bb Gametes: B b x B b Punnet Square: X B b B BB Bb b Bb bb F1 Genotype: 1 BB : 2 Bb : 1 bb F1 Phenotype: 3 Brown : 1 Blue
49. 49. Questions Brown (B) eyes is dominant to blue eyes (b). 1. If two heterozygous people mate, what is the ratio of their off spring? 2. If a homozygous brown eyed person mates with a blue eyed person what colour eyes will their offspring have? 3. What colour eyes will the offspring of a heterozygous brown eyed person who mates with a person with the recessive colour for eyes be? 4. If two blue eyed people mate, what colour eyes will their offspring have?
50. 50. Punnet Square Rules Heterozygous x Heterozygous cross = 3 dominant phenotype: 1 recessive phenotype Homozygous dominant cross = All dominant phenotype Heterozygous X recessive cross = 1 dominant phenotype: 1 recessive phenotype Recessive X recessive cross = All recessive phenotype
51. 51. Success Criteria Where do the genes for eye colour come from? What is the genotype of a person with brown eyes who has a sister with blue eyes? Why? How can two brown eyed people have a child with blue eyes? Complete page 50 of Workbook
52. 52. SLO Describe how gender is determined Explain sex chromosomes
53. 53. http://www.youtube.com/watch?v=8YMhkweABfQ
54. 54. Boy or Girl Parent Phenotype: Male X Female Parent Genotype: XY x XX Gametes: X Y x X X Punnet Square: X X X X XX XX Y XY XY F1 Genotype: 1 XY : 1 XX F1 Phenotype: 1 Male : 1 Female
55. 55. Boy or Girl Sex is determined by the male, if a sperm carrying a Y chromosome fertilizes an egg the baby is a _______________ if a sperm carrying an X chromosome fertilizes an egg the baby is a _______________ There is a 50% chance of a baby being a boy or girl, no matter how many boys in a row are born there will always be a 50% chance the next one will also be a boy
56. 56. Success Criteria How many pairs of chromosomes do humans have? If dogs have 54 chromosomes in their body cells, how many pairs of chromosomes do they have? How many chromosomes do they have in their sex cells?
57. 57. SLO Describe what a pedigree is
58. 58. Pedigree Key
59. 59. Pedigree Questions 1. What is the genotype of individual I2? Justify your answer 2. What is the genotype of individual III3? Justify your answer 3. What is the genotype of individual III4.?Justify your answer. 4. What is the genotype of individual III 1? Justify your answer I II II I
60. 60. Success Criteria
61. 61. Revision
62. 62. Multiple-choice quiz