What do these two famous people have in common Title Using genetics Thursday 23 rd January 2014 Homework Learning package 6 apart from 1c for Monday 27 th January Learning Outcomes ID: 907986
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Slide1
Learning question
: How can genetic diagrams be used to solve problems?
What do these two famous people have in common?
Title: Using genetics Thursday 23rd January 2014
Homework: Learning package 6 (apart from 1(c) ) for Monday 27th January
Slide2Learning OutcomesExplain the terms allele, locus, phenotype, genotype, dominant, codominant
and recessive; Explain the terms linkage and crossing-over;
Slide3StarterComplete the activity sheet on genetics.There are three parts to this activity:Vocabulary
Genetic diagramsCodomiance You will be tested on all three areas in your examination!
Slide4Progress tracker
0-55-1010-15
Slide5Monohybrid inheritanceMendel’s First Law principle of segregation“
The alleles of a gene exist in pairs but when gametes are formed, the members of each pair pass into different gametes, thus each gamete contains only one of each allele.”
Slide6Genetic Cross conventionsUse symbols to represent two allelesAlleles of the same gene should be given the same letter
Capital letter represents the dominant alleleSmall letter represents the recessive alleleChoose letters where the capital and small letter look differentThe examiner needs to be in no doubt about what you have written
Slide7Inheritance of height in pea plantsLaying out the crossP phenotypeP genotype
GametesF1 genotypeF1 phenotypeF1 self-fertilisedGametesRandom fertilisationF2 genotypic ratioF2 phenotypic ratio
Slide8Inheritance of height in pea plantsFollow out the following cross to the F2 generationHomozygous tall pea plant with a homozygous dwarf pea plantWrite out the genotypic and phenotypic ratios from the F2 generation
geneAllele
relationship
SymbolHeight of pea plants
TallDominant
T
dwarf
recessive
t
Slide9Pupil Activity – example question(a)In peas the height of the plant is controlled by one gene which has two alleles. T
represents the dominant allele for tall stems. t represents the allele for short stems. True breeding, tall-stemmed pea plants were crossed with short-stemmed pea plants to produce the F1 generation. (i) State the genotypes of the parents. (ii) State the phenotype of the F1 plants. Plants from the F1 generation were crossed to produce the F2 generation of plants. (iii) State the phenotypes and their expected ratio in the F2
generation.
Slide10Cystic FibrosisCystic Fibrosis is caused by a mutation to a gene on one of the autosomes.MutationChanges the shape of the transmembrane chloride ion channels (CFTR protein)The CFTR gene is found on Chromosome 7
The faulty gene is recessive
Slide11Inheritance of cystic fibrosisThree possible genotypesFF unaffectedFf unaffectedff
cystic fibrosisRemember gametes can only contain one allele for the CFTR geneAt fertilisation, any gamete from the father can fertilise any gamete from the motherThis can be shown in a genetic diagram
Slide12Genetic diagram showing the chances of a heterozygous man and a heterozygous woman having a child with cystic fibrosis.
Slide13Phenotype ratio of offspringGenotype ratio 1FF: 2Ff: 1ffPhenotype ratio 3 unaffected:1cystic fibrosisCan also be expressed as
25% chance of the child having cystic fibrosisProbability of 0.25 that a child will inherit the diseaseProbability that 1 in 4 that a child from these parents will have this disease.
Slide14Mini Plenary1. In tomato plants the allele for red fruit is dominant to the allele for yellow fruit. If a heterozygous tomato plant is crossed with a plant which produces yellow fruit, the expected phenotype ratio of the offspring would be
A 3 red : 1 yellow B 1 red : 3 yellow C 1 red : 2 yellow D 1 red : 1 yellow
Slide15Mini Plenary2. Achoo syndrome is a dominant characteristic in humans which causes the sufferer to sneeze in response to bright light. A woman who is homozygous for the syndrome and a man who is unaffected have children.
What proportion of their children would be expected to have Achoo syndrome? A 0% B 25% C 50% D 100%
Slide16Mini Plenary3. Which term refers to a description of a characteristic of an organism
? A genotype B phenotype C allele D natural selection
Slide17Mini Plenary4. Which term refers to forms of a gene controlling the same characteristic
? A genotypes B phenotypes C alleles D dominant
Slide18Learning OutcomeUse genetic diagrams to solve problems involving sex-linkage and codominance.
Slide19Sex-LinkageSex-linked genes are genes whose loci are on the X or Y chromosomesThe sex chromosomes are not homologous, as many genes present on the X are
not present on the Y.ExamplesHaemophiliaFragile X syndromeRed green colour blindness
Slide20Sex Chromosomes
Slide21Factor VIII and HaemophiliaHaemophilia is caused by a recessive allele of a gene that codes for a faulty version of the protein factor VIIIXH
normal alleleXh haemophilia alleleRemember, males are XY, females are XX
Slide22Possible genotypes and phenotypesApplying your knowledgeWrite out the genotypes for these phenotypes in hemophilia
Affected male_____________Normal male ______________Affected female ____________Normal female ____________Carrier female ____________
Slide23Inheritance of Haemophilia
Note! The stages for writing out a genetic diagram is the same
Slide24Pedigree for a sex linked recessive disease
Write out the genotypes for as many people in the family tree as possible.
Slide25Mini-plenaryCollect a “connect 4” board and question sheet.In pairs, test each others knowledge of genetics and try to win the game!
Slide26CodominanceCodominance describes a pair of alleles, neither of which is dominant over the other.
This means both have an effect on the phenotype when present together in the genotype
Slide27Codominance exampleFlower colour in plantsCR
redCw whiteGenotypesCRCR red flowersCRCW pink flowersCWCW white flowersWrite out a genetic cross between a pure breeding red plant and a pure breeding white plant. Carry out the cross to the F2 generation.Write out the genotype and phenotype ratio for the F2
generation
Slide28Revision QuestionCoat colour in Galloway cattle is controlled by a gene with two alleles. The CR allele produces red hairs and therefore a red coat colour. The C
w allele produces white hairs.A farmer crossed a true-breeding, red-coated cow with a true-breeding white-coated bull. The calf produced had roan coat colouring (made up of an equal number of red and white hairs).Explain the result and draw a genetic diagram to predict the outcome of crossing two roan coloured animals.
Slide29Inheritance of A, B, AB and O blood groupsHuman blood groups give an example of codominance and multiple allelesThere are 3 alleles present
IAIBIo
Slide30IA and IB are codominantIo is recessiveRemember each human will only have two alleles
Slide31Blood Groups
GenotypePhenotype
IAIA
Blood Group AIA I
oBlood Group A
IAI
B
Blood Group
AB
I
B
I
B
Blood Group
B
I
B
I
o
Blood Group
B
I
o
I
o
Blood Group
o
Slide32Inheritance of blood groupsCarry out genetic crosses for the following examples. Two parents have blood groups A and B, the father is IA
Io and the mother is IBIoFather has blood group AB and the mother has blood group OMother is homozygous blood group A and the father is heterozygous B.
Slide33Progress tracker
0-55-1010-15
Slide34Learning OutcomeDescribe the interactions between loci (epistasis). Predict phenotypic ratios in problems involving epistasis.
Slide35Dihybrid InheritanceMonohybrid crossInheritance of one gene
Dihybrid crossInheritance of two genes
Slide36Example – dihybrid crossTomato plants
Stem colourA purple stem a green stemLeaf shapeD cut leaves d potato leavesNOTEIn the heterozygote AaDd due to independent assortment in meiosis there are 4 possible gamete combinationsAD Ad aD ad
Slide37CrossesCross a heterozygous plant with a plant with a green stem and potato leavesCross two heterozygous tomato plants
Slide38Dihybrid InheritanceA woman with cystic fibrosis has blood group A (genotype IA
Io). Her partner does not have cystic fibrosis and is not a carrier for it. He has blood group O.Write down the genotypes of these two people.With the help of a full and correctly laid out genetic diagram, determine the possible genotypes and phenotypes of any children that they may have.
Slide39Autosomal linkageEach Chromosome carries a large number of linked genesIf two genes are on the same chromosome then independent assortment can not take place.
The genes are transmitted together and are said to be linked.
Slide40Linked GenesWhere linked genes are involved the offspring of a dihybrid cross will result in a 3:1 ratio instead of the 9:3:3:1 ratio.Example:
In peas, the genes for plant height and seed colour are on the same chromosome (i.e. linked)
Slide41Learning OutcomeDescribe the interactions between loci (epistasis). Predict phenotypic ratios in problems involving epistasis.
Slide42Flower colour in sweet peaFlower colourColourless precursor of a pigment CGene that controls conversion of this pigment to purple
PBoth dominant alleles need to be present for the purple colour to developCrossCross two white flowered plants with the genotypes CCpp and ccPPFollow this cross through to the F2 generation
Slide43Interactions of unlinked genesA single character maybe influenced by two or more unlinked genes.E.g. determination of comb shape in domestic poultryDominant allele P pea comb
Dominant allele R rose combTwo dominant alleles walnut combNo dominant alleles single comb
Slide44Genetic CrossesCarry out a genetic cross between a true-breeding pea comb and a true breeding rose combFollow this cross through to the F2 generation
Slide45Inheritance of coat colour in miceWild mice have a coat colour that is referred to as “agouti”.Agouti (A) is dominant to black (a)C is a dominant gene required for coat colour to develop
A homozygous recessive cc means that no pigment can be formed and the individual is albino
Slide46Inheritance of coat colour in miceCarry out a cross between a pure-breeding black mouse (aaCC) and an albino (AAcc)
Follow this cross through to the F2 generation.
Slide47EpistasisThis is the interaction of different gene loci so that one gene locus masks or suppresses the expression of another gene locus.Genes can
Work antagonistically resulting in maskingWork complementary
Slide48Epistasis ratios9 : 3 : 4 ratioSuggests recessive epistasis9 : 7 ratioSuggests epistasis by complementary action
12 : 3 : 1 ratio or 13 : 3 ratioSuggests dominant epistasis
Slide49Predicting phenotypic ratiosRead through pages 132 and 133 of your textbookAnswer questions 1 – 7
Complete the stretch and challenge question on “eye colour in humans”Read through and complete the worksheet provided for you on epistasis
Slide50Learning objectives
(e) use genetic diagrams to solve problems involving sex linkage and codominance;(f) describe the interactions between loci (epistasis). (Production of genetic diagrams is not required);(g) predict phenotypic ratios in problems involving epistasis;
Slide51Learning objectives
(e) use genetic diagrams to solve problems involving sex linkage and codominance;(f) describe the interactions between loci (epistasis). (Production of genetic diagrams is not required);(g) predict phenotypic ratios in problems involving epistasis;
Slide52GeneticsGenetics is the study of inheritanceAllele different varieties of the same gene
Locus position of a gene on a chromosome
Slide53GeneticsDominantAn allele whose effect is expressed in the phenotype if one copy presentRecessive
An allele which only expresses as a homozygoteCo-dominantBoth alleles have an effect on the phenotype
Slide54GeneticsGenotype genetic constitution of the organismPhenotype appearance of character resulting from inherited information
Slide55HomozygousIndividual is true breedingPossesses two alleles of a gene e.g. RR or rrHeterozygousTwo different alleles for a gene e.g. Rr