Inheritance

Name: __________________ Topic: Inheritance LO:Definea geneasa unitofinheritanceanddistinguishclearlybetweentheterms gene and allele ●A gene is aunit of inheritance.●Alleles aredifferent forms of the same gene.●Allelesoccupythe samerelativepositions/genelocion a pairof homologouschromosomes. LO: Explainthe termsdominant,recessive,codominant,homozygous,heterozygous, phenotype and genotype ●Dominantallelereferstoanallelethatexpressesitselfandgivesthesamephenotypeinboth homozygous and heterozygous conditions. ●Recessiveallelereferstoanallelethatonlyexpressesitselfinthephenotypeinthehomozygous condition. ●Codominanceis a conditionwherebothallelesexpressthemselvesequallyin thephenotype. Eg; I A and I B alleles in blood group ●Homozygousreferstoanorganismthathasidenticalallelesforaparticularphenotype/ trait. Concepts Summary NotesNan Hua High School Biology 1

Name: __________________ Topic: Inheritance ●Heterozygousrefersto an organismthathasdifferentallelesfor a particularphenotype / trait. ●Phenotypeistheexpressedtraitinanorganism. Eg;observablefeaturessuchaseyecolour and height. ●Genotype is thegenetic make-up of an organism. LO:Predicttheresultsofsimplecrosseswithexpectedratiosof3:1and1:1,using the terms homozygous, heterozygous, F1 generation and F2 generation ●To obtainanexpectedratioof3:1intheoffspringgeneration,bothparentsmustbeheterozygousfor a trait. Genetic diagram: Parent Male x FemalePhenotype Tall x TallGenotype Tt x Tt Gametes F1 genotype TT Tt Tt ttF1 phenotype tall tall tall shortPhenotypic ratio 3 tall: 1 short Concepts Summary NotesNan Hua High School Biology 2

Name: __________________ Topic: Inheritance ●To obtainanexpectedratioof 1:1in theoffspringgeneration,oneparentmustbeheterozygouswhilethe other is homozygous recessive. (test cross) Genetic diagram: Parent Male x FemalePhenotype Tall x shortGenotype Tt x tt Gametes F1 genotype Tt Tt tt ttF1 phenotype tall tallshort shortPhenotypic ratio 2 tall: 2 short= 1 tall: 1 short Note:Todetermineifthegenotypeishomozygousdominantorheterozygousdominant,atestcrosswithahomozygousrecessivecanbeused.Ifitishomozygousdominant,alltheoffspringwillshowthetrait.Ifitisheterozygousdominant,theratioofdominanttraitto recessive trait will be 1:1. Alternative Punnett Square Concepts Summary NotesNan Hua High School Biology 3

Name: __________________ Topic: Inheritance Concepts Summary NotesNan Hua High School Biology 4

Name: __________________ Topic: Inheritance LO:Explainwhyobservedratiosoftendifferfromexpectedratios,especiallywhen there are small numbers of progeny ● The genotype of every offspring is a result ofrandomfusion of nuclei of gametes.● Thus, the observed ratio and expected ratio may differ, especially when there areonly asmall number of offspring/ small sample size. LO:Usegeneticdiagramstosolveproblemsinvolvingmonohybridinheritance(genetic diagrams involving autosomal linkage or epistasis are not required)An example of genetic diagram;LetTbe the dominant tall alleleLettbe the recessive short allele Parent Male x FemalePhenotype Tall x TallGenotype Tt x Tt Gametes F1 genotype TT Tt Tt ttF1 phenotype tall tall tall shortPhenotypic ratio 3 tall: 1 short Pedigree chartDifference between conditions caused by dominant allele and recessive allele: Concepts Summary NotesNan Hua High School Biology 5

Name: __________________ Topic: Inheritance LO:Explainco-dominanceandmultiplealleleswithreferencetotheinheritanceoftheABObloodgroupphenotypes(A,B,ABandO)andthegenealleles(I A , I B and I o ) ● Gene that exists inmore than 2 types of alleles, is said to havemultiple alleles. Anexample of a trait with multiple alleles is blood group.● Blood group is controlled by three alleles,I A , I B , I O .● I A and I B are co-dominant and dominant over I O .● People with blood group AB will have bothI A and I B expressing equally, hence theyhaveboth antigen A and B. Hence, blood group AB isa form ofco-dominance. The Punnett square method Concepts Summary NotesNan Hua High School Biology 6

Name: __________________ Topic: Inheritance LO: Describe the determination of sex in humans – XX and XY chromosomesGenetic diagram:Parent Male (XY) x Female (XX)Phenotype Male x FemaleGenotype XY x XX Gametes F1 phenotype female female malemalePhenotypic ratio 2 female : 2 male= 1 female : 1 male ● Duringfertilisation,aneggwillcontributea X chromosomewhilea spermwillcontributeaXorYchromosome. Hence,sexinhumansisdeterminedbythesexchromosome the sperm carries.● Humans have22 pairs of autosomesand 1pair of sexchromosomes (XX/ XY). To find the probability of 2 traits, multiple the probability of each trait together.Eg;ProbabilityofabloodgroupOchildwhoisaboyborntobloodgroupAandblood group B parents =0.25 x 0.5 = 0.125 Concepts Summary NotesNan Hua High School Biology 7

Name: __________________ Topic: Inheritance LO:Describemutationasa changeinthestructureofa genesuchasinsicklecellanaemia,orinthechromosomenumber, suchasthe47chromosomesinthecondition known as Down syndrome ● Mutationisa suddenorspontaneouschangeingenestructureorchromosomestructure or number. Eg of gene mutation: sickle cell anaemia● Genethat codesfor normalhaemoglobinis mutatedto formabnormalhaemoglobin● Abnormal haemoglobin causes the red blood cell to be sickle shaped.● Sickle shaped red blood cellscarries less oxygenaround the body.● Homozygousrecessivediesyoung, heterozygoussurvivesin malariaproneareas.● Heterozygotes carry one mutated allele. They are known ascarriers. Eg of chromosomal number mutation: Down syndrome● 47 chromosomes instead of 46● Extra chromosome at chromosome number 21● Duetonondisjunctionduringmeiosiswhenhomologouschromosomesorsisterchromatids fail to separate during anaphase I / anaphase II. Concepts Summary NotesNan Hua High School Biology 8

Name: __________________ Topic: Inheritance LO:NameradiationandchemicalsasfactorswhichmayincreasetherateofmutationCauses of mutation:●Radiation (UV light, gamma rays)●