0

Commac

k High School HL

Biology

Topic Five: Gene

tics Notes

Seven

Quest

3.1 U.1 A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic. AND 3.1 U.2 A gene occupies a specific position on a chromosome. AND 3.1 U.3 The various specific forms of a gene are alleles. AND 3.1 U.4 Alleles differ from each other by one or only a few bases.

1. State definitions of the following: a. Chromosome (Slide 10)

b. Chromatid (Slide 11)

c. Gene (Slide 12)

d. Allele (Slide 14)

e. Gene locus (Slide 15)

2. Alleles of a gene vary only slightly from each other, but can produce very different characteristics. Complete the table by using your general knowledge state few examples of genes possibilities found on Chromosome 16. (Slides 12-15)

Chromosome Number

Percentage of Chromosome decoded

Number of possible genes

1295%

13 80%800

14 80% 1200

16

17 95% 1600

18 95%

X 1400

Y 50%

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3.2 U.1 Prokaryotes have one chromosome consisting of a circular DNA molecule. AND 3.2.U2 Some prokaryotes also have plasmids but eukaryotes do not. (Slide 16)

3. Distinguish between the two types of DNA present in a generalized prokaryote cell.

3.2 U.3 Eukaryote chromosomes are linear DNA molecules associated with histone proteins.

4. Describe the attraction of histones to DNA and explain the role it plays in the nucleus. (slides 17 & 18)

3.2 U.4 In a eukaryote species there are different chromosomes that carry different genes. 5. What are the numbers of genes found on chromosome number 1 and 4?

6. Outline the three ways in which chromosomes can vary: (Slide 22)

7. If chromosomes vary, describe how individuals of a species are similar in terms of their DNA. (Slide 22)

3.1. U.6 The genome is the whole of the genetic information of an organism. AND 3.1. U.7 The entire base sequence of human genes was sequenced in the Human Genome Project. AND Nature of Science: Developments in scientific research follow improvements in technology - gene sequencers are used for the sequencing of genes. (1.8)

8. State the definitions of the genome? (Slide 23)

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3.2 A.2 Comparison of genome size in T2 phage, Escherichia coli, Drosophila melanogaster, Homo sapiens and Paris japonica.9. Complete the table to compare genome size in the selected organisms. (Slide 24)

OrganismGenome size(million base

pairs)

Genome SizeNumber of Chromosomes

Virus - T2 phage .18Bacterium - Escherichia coli 5 4,377

Fruit fly(Drosophila melanogaster)

17,000

Humans(Homo sapiens) 150,000Canopy plant(Paris japonica) 3,000

Although the genetic code is universal the number of genes held by different species varies greatly. State the name and approximate number of genes held by: (Slides 25-31)

Organism Genome size(million base pairs)

Genome SizeNumber of

ChromosomesM. musculus (Mouse)

23,000

Arabidopsis (Plant) 25,000C. elegans (Roundworm) 97 millionE. Coli (Bacteria) 4.6 million 3,200H. influenza (Bacteria) 1.8 million

Species Name Number of Chromosomes

Homo sapiens (You) 46

Pan troglodytes (Chimp)

Canis familiaris (Dog) 78

Oryza sativa(Rice)

Parascaris equorum 2

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10.The Human Genome* Project (HGP) was an international 13-year effort, 1990 to 2003. State it’s primary goals. (Slide 34)

3.1 U.7 The entire base sequence of human genes was sequenced in the Human Genome Project.

11.Key to the success of the Human Genome* Project (HGP) was the use of gene sequencers. List the key advances in technology made their use possible. (Slide 35)

3.1 S.1 Use of a database to determine differences in the base sequence of a gene in two species. (Slide 36)

GenBank is the NIH genetic sequence database, an annotated collection of all publicly available DNA sequences. Use it to find and extract base sequences by following the below steps: Go to GenBank website http://www.ncbi.nlm.nih.gov/genbank Select ‘Gene’ from the search bar Enter the name of a gene (e.g. AMY1A for salivary amylase 1A or COX1 for cytochrome oxidase 1)

AND the organism (use the binomial) and press ‘Search’n.b. if you are comparing species the gene chosen needs to be the same for each species

Select the ‘Name/Gene ID’ to get a detailed view Scroll down to the ‘Genomic regions, transcripts, and products’ section and click on ‘FASTA’ Copy the entire sequence from ‘>’ onwards Save the sequence – you will need to align with the other species next

A. Your task is to analyse the differences between three or more species (the skill asks for two species, but the online Clustal tool works better with a minimum of three). List the three species chosen and the gene you are choosing to work with:

B. Species (give common names and the binomial)C. Gene (give both the name and the code)

To align the sequences: Go to the Clustal Omega website http://www.ebi.ac.uk/Tools/msa/clustalo/ In STEP 1 Select ‘DNA’ under ‘a set of’ Paste the chosen sequences into the box (each sequence must start on a new line) Press ‘Submit’ (and wait – depending on the size of the sequences you may have to wait for a

couple of minutes)Analysis:

‘Alignments’ allows you to visually check the results – this is easier if the chosen gene has a short base sequence

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Under ‘Results Summary’ use the ‘Percent Identity Matrix’ to quantify the overall similarity (0 = no similarity, 100 = identical)

Under ‘Phylogenic Tree’ chose the ‘Real’ option for the Phylogram to get a visual representation of how similar the species are (based on the chosen gene). Align the sequences, analyse the results and outline your findings below:

3.2 U.6 Diploid nuclei have pairs of homologous chromosomes. AND 3.2 U.7 Haploid nuclei have one chromosome of each pair.

12.Eukaryotic nuclei can be described as being haploid or diploid. Describe what is meant by these terms (Slide 45)

3.2 U.8 The number of chromosomes is a characteristic feature of members of a species.

13.List the types of cell in humans that are diploid and state the number of chromosomes present in the

nuclei. (Slide 45) ex.

3.3 U.1 One diploid nucleus divides by meiosis to produce four haploid nuclei.

14.State the function of meiosis. (Slides 49-50)

Explain why meiosis is described as a reduction division. (Slides 49-51)

3.2 U.5 Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes.

3.3 U.2 The halving of the chromosome number allows a sexual life cycle with fusion of gametes.

15.Complete the table to show how the chromosome number changes during a sexual life cycle. (Slide 52)

Stage of the sexual life cycle Chromosome number (n/2n)

Haploid or Diploid

Adults 46 diploidGametes (egg and sperm cells) 23

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Zygote diploidJuvenile 46

16.Explain what would be the consequence to the sexual life cycle if meiosis failed to reduce the chromosome number

10.1 U.1 Chromosomes replicate in interphase before meiosis.

17.State which part of interphase chromosomes replicate in. (Slides 53-54)

3.2 A.1 Cairns’ technique for measuring the length of DNA molecules by autoradiography. AND Nature of Science: Developments in research follow improvements in techniques - autoradiography was used to establish the length of DNA molecules in chromosomes. (1.8)

18.John Cairn technique are essential for the use of? (Slide 55)

3.3 U.7 Crossing over and random orientation promotes genetic variation. 10.1 U.2 Crossing over is the exchange of DNA material between non-sister homologous chromatids.10.1 U.4 Chiasmata formation between non-sister chromatids can result in an exchange of alleles. 10.1 U.3 Crossing over produces new combinations of alleles on the chromosomes of the haploid cells.

19. Crossing over occurs in Prophase I. State the result of the process and explain how this increases the genetic variation found in gametes. Include the Synapsis & Chiasma formation (Slides 59-61)

20.Outline a chiasmata and what happens at the end of anaphase 1. (Slide 62)

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10.1 U.5 Homologous chromosomes separate in meiosis I, 10.1 U.6 Sister chromatids separate in meiosis II.

21.State the phase of meiosis does reduction division take place, i.e. when are the number chromosomes reduced. (Slide 63)

22.Explain why Meiosis II is not classed as being a reduction division. (Slide 66)

10.1 U.7 Independent assortment of genes is due to the random orientation of pairs of homologous chromosomes in meiosis I.

23.Mendel made many advances in genetics through careful observation and statistical analysis.

a. State Mendel’s Law of Independent Assortment (Slides 64-69)

b. Independent assortment can result in unusually combinations. State an example (Slides 68-69)

3.3 S.1 Drawing diagrams to show the stages of meiosis resulting in the formation of four haploid cells. AND 3.3 U.3 DNA is replicated before meiosis so that all chromosomes consist of two sister chromatids. AND 3.3 U.4 The early stages of meiosis involve pairing of homologous chromosomes and crossing over followed by condensation. AND 3.3 U.5 Orientation of pairs of homologous chromosomes prior to separation is random. AND 3.3 U.6 Separation of pairs of homologous chromosomes in the first division of meiosis halves the chromosome number.

24.Outline the events and movements of chromosomes occurring during the different stages of meiosis

(Slides 71-81)

Meiosis IPhase Events Labelled Diagram

Prophase I

Metaphase I

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Anaphase I

Telophase I

Meiosis IIPhase Events Labelled Diagram

Prophase II

Metaphase II

Anaphase II

Telophase II

Cytokinesis

25.Complete the table to compare and contrast mitosis and meiosis: (Slide 82)

Mitosis Meiosis

Number of divisions One division Two divisions

Number of daughter cells 4

Chromosome number in daughter cells

Diploid cells produced

Chromosomes exact copy or changed:

Exact copy changed

Functions/Uses: Growth, repair, asexual reproduction,

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zygote development

3.3 U.8 Fusion of gametes from different parents promotes genetic variation.

26.Outline how sexual reproduction leads to even further genetic variation within a species. (Slides 83-86)

3.3 A.1 Non-disjunction can cause Down syndrome and other chromosome abnormalities.

27.Annotate the diagram below to show what happens in non-disjunction in meiosis II. (Slide 87)

28.Describe how non-disjunction and fertilization lead to trisomy, between non-disjunction and trisomy. (Slide 87)

3.2 U.9 A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length.

29.Distinguish between a karyogram and a karyotype. (Slide 89)

30.State three visual aspects of homologous chromosomes which can be used to identify them for the purpose of a karyotype? (Slide 89)

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3.2 U.10 Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex.

31.One pair of chromosomes in human cells is not always homologous. State which pair. (Slide 92)

32.State the gene, if expressed that causes the development of male characteristics and the chromosome it is located on. (prior knowledge)

3.2 A.4 Use of karyograms to deduce sex and diagnose Down syndrome in humans.

33.Analyse the karyogram below: (Slides 89-93)

Gender: Condition:

3.3 A.3 Description of methods used to obtain cells for karyotype analysis e.g. chorionic villus sampling and amniocentesis and the associated risks. (Slides 94-96)

34.A karyotype can be used to test for non-disjunction disorders. Fetal cells are taken and the number of chromosomes counted. Outline how these cells are retrieved and the risks involved:

Chorionic Villus Sampling (CVS):  

Amniocentesis:

3.3 A.2 Studies showing age of parents influences chances of non-disjunction.

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35.The graph shows the effect of maternal age on the % risk of a pregnancy resulting in Down syndrome and other trisomy’s.

36.Outline the effect of maternal age on likelihood of Down syndrome. (Slide 97)

37.Evaluate the risk of a Down Syndrome to a 46 year old pregnant woman with the risk of a miscarriage caused by amniocentesis (1%) and chorionic villus sampling (2%).(Slide 97)

3.4 U.1 Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed. https://www.youtube.com/watch?v=NWqgZUnJdAY

Use the hyperlink above to answer the following questions about Mendel’s experiments (Slide 101)

38.The term ‘pure-bred’ refers to a living thing carrying only one type of gene (Example two Big Ys YY equals green or two little y’s yy equals yellow. What happened when he crossed the two alleles? (52 secs)

39.What happen in the second generation cross between the two yellow parents? What was the trait that reappeared called (1:09).

40.What is a punnet square used for in Mendel’s experiments? (1:42)

41.What happen when introduce more characteristics (2:30)

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3.4 U.2 Gametes are haploid so contain only one allele of each gene. 3.4 U.3 The two alleles of each gene separate into different haploid daughter nuclei during meiosis. 3.4 U.4 Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles.

42.State definitions of the following and fill in the diagram below: (Slides 102-107)

Genotype

Phenotype characteristics or traits of an organism

Dominant allele

Recessive allele only when present in the homozygous state

Homozygous

Heterozygous two different alleles of a gene

Carrier individual who has a recessive allele of a gene that does not have an effect

Test Cross

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3.4 S.1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.

43.Outline Mendel’s laws (Slide 113)Law of Segregation Law of Dominance  Law of Independent Assortment

44.Complete the punnet grid below to show the outcome of the monohybrid cross that results in peas of different colors. (Slide 114)

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45.Complete the punnet grid below to show the possible outcomes of a cross between two members of the F1 generation. Describe all genotypes produced. (Slide 114)

46.What is a test cross (Slide 116)

47.Explain how a test cross could be used to determine the genotype of a yellow pea with a genotype of YY or Yy. (Example on Slides116-118)

3.4 A.1 Inheritance of ABO blood groups. AND 3.4 U.5 Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects.

48.What is the codominant inheritance pattern Human ABO blood types? (Slide 121)

49.Describe what is meant by “some genes have multiple alleles.” (Slide 124)

50.Complete the table (both genotype and phenotype) below to show how blood type is inherited.

alleles i IA IB

i ii IBiIA IAi IAIA IAIB

IB IAIB

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51.State the genotype and phenotype which is an example of codominance. (Slides 126-128)

52.Complete this pedigree chart to show the inheritance of blood types in this family.

3.1 A.1 The causes of sickle cell anemia, including a base substitution mutation, a change to the base sequence of mRNA transcribed from it and a change to the sequence of a polypeptide in hemoglobin. AND 3.1 U.5 New alleles are formed by mutation.

53.

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mRNAamino acid

54.Distinguish between the two DNA strands above in terms of:

55.DNA base sequence.

56.Amino acid sequence in the resulting polypeptide.

Watch: Malaria and Sickle Cell Anemia https://www.youtube.com/watch?v=Zsbhvl2nVNE57.What is sickle cell? (1:15)58.What is the percentage of African American carriers of Sickle Cell in the U.S.? (1:43)

59.Where in Africa did the scientist find high levels of Sickle Cell carriers? (5:11)

60.What may of the causes for high levels of carriers in these areas ? (5:50)

61.What happened to the Malaria parasite count in children carrying the sickle cell gene? (7:59)

62.Describe the results of two carriers having offspring. (9:30)

63. Outline the causes for a new mutation (Slide 130)

64. Provide several examples of mutations in a gene that could occur (Slide 131)

65.Describe the effects of sickle cell disease on sufferers in terms of: (Slide 132)

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66.Describe a base substitution mutation. (Slides 133)

67.Outline how a base substitution mutation can result in a new allele. (Slide 133)

68.Outline how a base substitution mutation that results in Sickle Cell Anemia. (Slides 134-135)

69.Some people inherit both a normal allele (HbA) and a sickle cell (HbS) allele. Such people do show very few symptoms of sickle cell disease. What it the genetic arrangement of those people (Slide 138)

70. Identify parts of the world this genotype could be beneficial. (Slide 141)

71.State the genotypes description, phenotypes and malaria protection of these individuals.

genotype HbAHbA HbAHbs HbsHbs

description

phenotype

Malaria protection?

Allele key: HbA produces normal haemoglobin, HbS produces fibrous haemoglobin that causes red blood cells to sickle.

72.Predict the phenotype ratios of offspring using a punnet square in the following crosses. Show all your working, and set it out as expected. Take care with notation.

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i. Carrier mother with affected father.ii. Affected father with unaffected mother.iii. Carrier mother with carrier father.

3.4 U.8 Many genetic diseases have been identified in humans but most are very rare.

73.Explain why genetic diseases are very rare in humans. (Slide 145)

3.4 U.7 Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes. AND 3.4 A.2 Red-green color blindness and hemophilia as examples of sex-linked inheritance.

74.Some inherited disorders are associated with gender. State two examples of sex-linked genetic disorders and describe them. (Slides 147-149)

75.Explain why sex-linked disorders are more common in males than females. (Slides 150)

76.Explain why human females can be homozygous or heterozygous for sex-linked genes, where males cannot. (Slides 1451-152)

77.What are the sex linked arrangement for male and female individuals that have hemophilia and color blindness (Slide 153)

78.The allele for color blindness (n) is recessive to the allele for normal vision (N). This gene is carried in a non-homologous region on the X chromosome. Complete the table below to show the genotypes and phenotypes of individuals with regard to color blindness.

Female Male

Normal XNy

Affected

Carrier XNXn

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79.Some inherited disorders are associated with gender. State two examples of non sex-linked genetic disorders and describe them. (Slides 158-159)

80.What is a pedigree chart? (Slide 160)

81.The pedigree chart below shows a family affected by sickle cell:

Deduce the genotype of each individual with a letter.

A FB GC HD $E #

82.Calculate the likelihood of any further children produced by E and her # having sickle cell anemia.

83.Male $ is healthy but of unknown genotype. Calculate the likelihood of any children produced with female D having s

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3.4 S.3 Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.A pedigree is a chart of a person’s ancestors that is used to analyze genetic inheritance of certain traits – especially diseases. The symbols used for a pedigree are:

female, unaffected

female, affected

male, unaffected

male, affected

Siblings are placed in birth order from left to right and are labeled with numbers. Each generation is labeled with a Roman numeral.

Example: we would name an individual II-3 if he/she was in the second generation and the 3rd Child born

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Try to identify the genotypes of the following individuals using the pedigree above.(homozygous dominant, homozygous recessive, heterozygous)

III-3: _______________II-1: _________________I-1: __________________

a. Is this trait dominant or recessive? Explain your answer.

b. How can you know for sure that individuals II-3 and II-4 are heterozygous?

c. Brown eyes are a dominant eye-color allele and blue eyes are recessive. A brown-eyed woman whose father had blue eyes and whose mother had brown eyes marries a brown-eyed man whose parents are also brown-eyed. They have a son who is blue-eyed. Please draw a pedigree showing all four grandparents, the two parents, and the son. Indicate which individuals you are certain of their genotype and where there are more than one possibilities.

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3.4 U.9 Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer.

84.State the definition of a mutation. (Slide 166)

85.Mutagens are agents that cause gene mutations. List three types of mutagen.(Slide 167)

86. Describe indirect and direct damage to DNA when exposed to a mutagen. (Slide 169)

87.Draw a few examples of complete and broken chromosomes (Slides 170-171)

3.4 A.4 Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl.

88.How dose of radiation from an x-ray compare to that of Hiroshima and Chernobyl victims (Slides 172-177)

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89.Radiation releases into the environment by humans can causes major problems. Radiation pollution is commonly the result of an accident at a nuclear power station (Chernobyl) or a deliberate after affect caused by the release of a nuclear bomb (Hiroshima). Outline the impacts and evidence of them caused by each incident plus make notes on the limitations of evidence. (Slides 174-179)

Accident at Chernobyl nuclear power station Release of a nuclear bomb at Hiroshima

Impacts and supporting evidence

• A large area of pine forest downwind of the reactor turned

brown and died.• Horses and cattle near the plant

died from radiation damage to their thyroid glands.

Bioaccumulation of radioactive caesium in fish (Scandinavia and Germany) and lamb (Wales) - contaminated meat was banned from sale for years afterward

Limitations of the evidence / what cannot be concluded*

No clear evidence to support an increase in the rate of leukemia other cancers – in part due to the widely dispersed variable

radiation and measures taken in European populations

*10.2 U.2 Unlinked genes segregate independently as a result of meiosis.

90.Mendel’s Law of Independent Assortment (review)

10.2 U.3 Variation can be discrete or continuous. AND 10.2 U.4 The phenotypes of polygenic characteristics tend to show continuous variation.

91.Distinguish between Discrete/Continuous Variation (Slide 185)

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10.2 A.3 Polygenic traits such as human height may also be influenced by environmental factors.

92.Most traits, including polygenetic traits such as height, maybe influenced by the environment of the organism. Complete the table to give examples of the ways in which this can happen.(Slides 186-188)

Human Trait Influencing Environment factors

Heightthe effect of environmental facts on the height of these identical twin due to diet

Skin color

Apple Size Exposure to light

93.Define polygenic inheritance. (Slide 189)

94.Distinguish between polygenic inheritance and multiple alleles. (Slide 189)

10.2 A.2 Completion and analysis of Punnett squares for dihybrid traits. AND 10.2 S.1 Calculation of the predicted genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes.

95.Distinguish between dihybrid and monohybrid crosses. (Slide 190)

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96.When Mendel came upon his law of independent assortment, he was studying sweet-pea colour and shape. These traits are carried on separate chromosomes. The color yellow (Y) is dominant over green (y). Smooth peas (S) are dominant over rough (s). (Slides 190-193)

97.State the possible genotypes for the following phenotypes:

Yellow, Smooth YY or Yy/SS or Ss Green, Smooth

Green, rough Yellow, rough YYss or Yy/ss

98.Use the Punnett grid to predict the ratio of phenotypes of offspring in a cross between two peas which are heterozygous for both genes (SsYy x SsYy). (Slides 190-193)

i. SY Sy sY sy

SY SsYY SsYy

Sy SSYy SSyy SsYs Ssyy

sY SsYy SsYy ssYy

sy ssYy Ssyy ssYy

Phenotype Smooth Yellow Smooth green Rough Yellow Rough Green

Ratio

99.A researcher has some smooth yellow peas. He wants to find out if they are homozygous or heterozygous for these dominant characteristics, so he performs a test cross. State the genotype and phenotype of the plant that must be used as the test cross.

Genotype: Phenotype:

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100. Explain how polygenic inheritance gives rise to continuous variation within a population using skin color as an example. (Slide 219)

101. Assume that two genes (A and B) are responsible for inheritance of skin color, with two alleles each and that they are unlinked. The dominant alleles code for melanin production. Calculate the number of possible genotypes in diagram below.

Aabb

Pick a pair of genotypes from question 100. Using a punnet grid, explain why it is possible for children to have skin which is darker or lighter than both parents. (Use Slides 220-221 for help)

Mother genotype: Father genotype:

Outcome and explanation:

ii.

102. Deduce the number of possible genotypes and phenotypes (Skin type)

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Dark Black

Light Black

Dark Brown

Light Brown

White

103. A characteristic is controlled by three genes with two alleles each. Calculate the number of genotypes possible in a cross between a homozygous recessive father and a homozygous dominant mother.

Nature of science: Looking for patterns, trends and discrepancies - Mendel used observations of the natural world to find and explain patterns and trends. Since then, scientists have looked for discrepancies and asked questions based on further observations to show exceptions to the rules. For example, Morgan discovered non-Mendelian ratios in his experiments with Drosophila. 10.2 A.1 Morgan’s discovery of non-Mendelian ratios in Drosophila.

104. Morgan’s experiments (1909-1914) with fruit flies produced results that could not be explained by Mendel’s work on heredity as it stood. Morgan’s key insight came after breeding a white-eyed male mutant with red eyed female flies. Complete the table to outline his observations and where the explain the conclusion: (Slides 222-223)

Observation Deduction – consistent or inconsistent with Mendelian law?

The 1st generation offspring all had red eyes

The 2nd generation contained a small number (roughly 25% of flies) with white eyes

However all the white-eyed flies were male

10.2 U.1 Gene loci are said to be linked if on the same chromosome. AND 10.2 S.2 Identification of recombinants in crosses involving two linked genes.

Mendel’s law of independent assortment makes the assumption that genes for a pair or group of traits are being carried on separate chromosomes, and therefore the presence of one allele in a gamete is not connected to the presence of another. However, with hundreds of genes per chromosome, it is likely that some genes will be physically linked and therefore alleles will be inherited together.

105. Define linked genes. (Slide 223) are located on the same chromosome and do not sort independently

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106. The term linkage is used in various ways in genetics. Distinguish between autosomes and sex chromosomes. (Review slides 147-149 and 223)

107. The notation shows genes of Zea mays (corn). It is described as “heterozygous at both loci”. These are both traits related to the corn kernels.

Key: C = color, c = no color; W = waxy, w = no wax.

108. Draw some other possible combinations of these linked genes:

Homozygous dominant at both loci

Homozygous recessive at locus 1.

your choice

109. Complete a punnet grid to show the possible phenotypes produced by a cross between the corn that is heterozygous at both loci. Use correct notations and show your working.

i.

Phenotype

Ratio

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110. List the combinations of alleles which are not possible in the cross above (unless recombination takes place at Prophase I).

111. State the stage of meiosis during which crossing over and exchange of alleles can occur.

112. Complete the punnet grid below:

P L p l

p l PpLl

p l

no recombination with crossing over (recombinants)

10.2 U.5 Chi-squared tests are used to determine whether the difference between an observed and expected frequency distribution is statistically significant. AND 10.2 S.3 Use of a chi-squared test on data from dihybrid crosses. (Slides 231-237)

113. In corn ears there are four main phenotypes: purple and smooth, purple and shrunken, yellow and smooth, yellow and shrunken. You will examine an ear of corn and determine the type of cross and genes responsible for the coloration and texture of the corn kernels and also whether the corn kernel color and texture follows the expected pattern of dihybrid inheritance. Use the image below to take the sample for your investigation.(activity based on: http://www.biologycorner.com/worksheets/ corn_chi.html )

Use the picture below from the hyperlink below https://www.biologycorner.com/wp-content/uploads/corn-ear-carolina.jpg

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114. Select five rows on the corn ear to sample for coloration (purple or yellow) and texture (smooth or shrunken) and record your findings in the tables below. The sample used must be the same for both characteristics.

Kernel Colouration

Number of Kernels Kernel Percentage (%)

Purple

Yellow

Total

Kernel Texture

Number of Kernels Kernel Percentage (%)

Smooth

Shrunken

Total

115. Assuming that purple (P) is dominant to yellow (p) and smooth (S) is dominant to shrunken (s) complete a dihybrid cross between two heterozygous parents and calculate the expected phenotype ratio

i.

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Phenotype

Ratio

116. Using the same five rows as earlier count the phenotypes present and calculate the percentage frequency of each.

Observed phenotype frequency

Number of Kernels Kernel Percentage (%)

Purple and Smooth

Purple and shrunken

yellow and Smooth

yellow and shrunken

Total

Did you obtain a 9:3:3:1 ratio? To determine if the deviations between expected frequencies and the observed data are due to natural variation or whether the difference is statistically significant use a chi-squared test.

117. Calculate the chi-squared value using the table below:

Chi-squared calculations

Expected(number of kernels)

Observed(number of kernels)

(Observed – Expected) 2 Expected

Purple and Smooth total x 9/16 =

Purple and shrunken total x 3/16 =

yellow and Smooth total x 3/16 =

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yellow and shrunken total x 1/16 =

Total Chi-squared =sum of (O-E)2/E

118. Calculate the degrees of freedom.

df = Number of classes (phenotypes) – 1 =

119. Is the (expected) theory of dihybrid corn kernel colouration and texture inheritance supported by the (observed) data?(is Chi-square value < critical value)

3.5 U.2 PCR can be used to amplify small amounts of DNA.

120. The polymerase chain reaction (PCR) is used where DNA samples are too small to be useful. State the purpose of PCR in labs and investigations. (241)

121. Identify the cellular process which PCR mimics. (Think cell cycle)

122. State the role of high temperatures in PCR.(242)

123. State the role of complementary base pairing in PCR. (Hyperlink on slide 242)

124. Describe why it is called a chain reaction. (Hyperlink on slide 242)

3.5 U.1 Gel electrophoresis is used to separate proteins or fragments of DNA according to size. AND 3.5 U.3 DNA profiling involves comparison of DNA.

125. State two main uses of DNA profiling by electrophoresis. (Slides 247-248)

126. State the roles of the following components of gel electrophoresis: (Slides 243-245)

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df critical values at 5%

1 3.84

2 5.99

3 7.82

4 9.49

5 11.07

Component Role

Restriction enzymes Cut DNA into fragments

Gel

Electric current fragments of DNA will move through the gel based on size and charge

Fluorescent DNA markers

3.5A.1 Use of DNA profiling in paternity and forensic investigations. 127. Outline why DNA profiling is useful in forensic investigations. (Slide 248)

128. DNA profiling can exclude certain candidates and give evidence to suggest the most likely father, or mother, of a child. List the circumstances in which DNA profiling is useful to a paternity investigation: (Slide 248)

3.5 S.2 Analysis of examples of DNA profiles.

129. Use the gel electrophoresis results below to answer these questions. In this case, a DNA sample was taken from a cigarette found at a crime scene (smoking in a no-smoking zone): (Slides 250-252)

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130. State the process used to amplify the small amounts of DNA collected at the crime scene to an amount big enough to be used in DNA profiling.

131. Deduce which criminal, Rob McCarr or Nick Allott, left their cigarette-end at the crime scene. Explain your answer.

Criminal:Explanation:

132. Draw bands to show where the standard fragments would be observed. State the role of the standard fragment.

133. Outline the evidence in the DNA profile that suggests Nick and Rob are related. (Slide 252)

3.5 U.4 Genetic modification is carried out by gene transfer between species. AND 3.5 A.2 Gene transfer to bacteria using plasmids makes use of restriction endonucleases and DNA ligase.

134. State the role of the following in gene transfer: (slide 256-258)A. Restriction enzymes used to cut strands of DNAB. E. coli plasmids C. Ligase joins DNA fragmentsD. Vector:

135. Annotate the diagram below to outline the process of gene transfer:( (slide 260-262)

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136. Genetically modified organisms (GMOs) are created using gene transfer. Outline gene transfer. (Slides 263-266)

137. Explain how the universality of the genetic code is central to gene transfer applications.(Hint: Think central dogma)

138. Define transgenic organism. (Slide 267)

139. Give four examples of genetically modified (GM) organisms and the effects of their new genes.(Slide 267)

Genetically modified organism New property Advantages

Rice contains β-carotene (a precursor to vitamin A)

tomato plants Grow in areas flood by the ocean

Goats milk containing spider silk protein

Bacteria for diabetics

3.5 A.3 Assessment of the potential risks and benefits associated with genetic modification of crops. AND Nature of science: assessing risks associated with scientific research - scientists attempt to assess the risks associated with genetically modified crops or livestock. (4.8) AND 3.5 S.3 Analysis of data on risks to monarch butterflies of Bt crops. (Slides 268-272)

Bt corn is an example of the genetic modification of crop. Bacillus thuringiensis (Bt) is a soil bacterium that produces insecticidal toxins. Genes from Bt have been inserted into maize so GM plants can produce an insecticidal toxin and therefore be resistant to pests, e.g. European Corn Borer.

140. Identify which potential benefits apply when assessing the usefulness of Bt corn and outline how the introduced trait is a benefit.

Potential benefit Potential Harm

Resistant to pests Gene Flow (mixing of genes from GMO and wild type)

Killing of other organisms

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Increase production

141. The ecological impact of GMOs Good or Bad? Genetic Engineering & Our Food (Slide 268 hyperlink)

a. How long have we been genetically modifying organisms (0:42)

b. What is gene flow (1:42) c. Is eating GMO plants risky (3:09) d. What saved the Bangladesh Eggplant? e. What are a couple of examples of future uses for GMO’s?

142. Explain why monarch butterflies could be at risk from Bt corn. (Slide 268 Bill Nye video 6:51 in the hyperlink )

143. Describe the trends seen in the lab study. (Slide 270)

144. Describe the trends seen in the field studies (slide 271).

145. Suggest reasons why Monarch caterpillars’ Bt toxicity is easier to detect in laboratory studies.(Slide 271)

146. Evaluate the hypothesis that Bt Corn adversely affects Monarch butterfly populations.

3.5 U.5 Clones are groups of genetically identical organisms, derived from a single original parent cell. AND 3.5 U.6 Many plant species and some animal species have natural methods of cloning. AND 3.5.U7 Animals can be cloned at the embryo stage by breaking up the embryo into more than one group of cells.36

147. State the Definition of the term clone.(Slide 273) 148.

149. Complete the table to describe four examples of naturally occurring clones. (Slides 273)

Natural clone example Description

Starfish piece breaks offBacteria (Binary fission)

(plant) Runners plants grow horizontal stems called runners that grow roots

(plant) Tubers

150. Outline how embryos can be cloned artificially.(Slides 274)

3.5 U.8 Methods have been developed for cloning adult animals using differentiated cells. AND 3.5.A4 Production of cloned embryos produced by somatic-cell nuclear transfer. (Slides 280-281)

151. Cloning by somatic-cell nuclear transfer (SCNT) allows the creation of a genetically identical organism through transfer of a differentiated diploid nucleus. State the definition of the term differentiated diploid nucleus.

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152. Outline the steps involved in SCNT(Slide 284)

153. Dolly the sheep was the first successful cloning of a mammal from a differentiated somatic cell. Suggest one reason why Dolly died younger than normal, but of an age-related illness (Slide 283 hyperlink)

154. Differentiate between the process of SCNT and therapeutic cloning.

155. Cloning of a whole organism has limited use, but there are many potential uses of uses of therapeutic cloning in medicine. List the uses of therapeutic cloning.

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