7.014 Genetics Section ProblemsFor each set of data below, determine the genotype of the parents in cross 1. Where itapplies, indicate which phenotypes are dominant and which are recessive.Mice Ia) cross 1: red-eyed mouse ____________ X white-eyed mouse ____________gives F1: all red-eyedcross 2: red-eyed F1 X red-eyed F1gives F2: 36 red-eyed13 white-eyedb) cross 1: long-eared mouse ____________ X short-eared mouse ____________gives F1: 12 long-eared10 short-earedcross 2: long-eared F1 X long-eared F1gives F2: 36 long-eared13 short-earedFlowerscross 1: blue-flowered plant ____________ X white-flowered plant____________gives F1: all pale-blue-floweredcross 2: pale-blue F1 X pale-blue F1gives F2: 27 blue49 pale-blue24 whiteBlood Typea) cross 1: person, type A blood ____________ X person with type B____________gives F1: all type AB bloodcross 2: type AB F1 X type AB F1gives F2: 2 type A4 type AB1 type BBlood Type, continuedb) cross 1: type A blood ____________ X type B ____________gives F1: 2 type A blood3 type AB blood1 type B blood2 type O bloodMice IIa) cross 1: tail-less mouse ____________ X normal mouse ____________gives F1: 10 tail-less9 normalcross 2: tail-less F1 X tail-less F1gives F2: 10 normal21 tail-less9 deadb) cross 1: blue-eyed, long-toothed mouse X brown-eyed, short-toothed mouse ____________ X ____________gives F1: all blue-eyed, short-toothedcross 2: blue-eyed, short-toothed F1 X blue-eyed, short-toothed F1gives F2: 92 blue-eyed short-toothed31 blue-eyed long-toothed29 brown-eyed short-toothed9 brown-eyed long-toothedPlantscross 1: tall, green plant ____________ X short, yellow plant____________gives F1: 20 tall green20 short greencross 2: tall, green X short, yellow (different plants than (b))gives F1: 19 tall green21 tall yellowSolutions to Genetics Section ProblemsMice Ia) Cross 1: red eyes X white eyes gives all red eyes – a likely model is that eye color iscontrolled by one gene that has 2 alleles resulting in two phenotypes, red eyes and whiteeyes. The red eyed phenotype is likely to be dominant. Therefore, choose appropriatesymbols (one letter per gene, capital letter for allele with dominant phenotype):R - red allele. Dominant phenotype of red eyes.r - white allele. Recessive phenotype of white eyes.Cross 1 is then: RR X rr ----> all Rr (all red eyes).Cross 2 is then: Rr X Rr ----> 3:1 red:white.The predictions agree with the data.b) Cross 1: long ears X short ears gives some long and some short ears – a likely model isthat ear length is controlled by one gene with 2 alleles resulting in two phenotypes, longears and short ears. From this data, we cannot determine which allele has the dominantphenotype.Cross 2: long ears X long ears gives some long and some short ears – a likely model is thatlong ears is the dominant phenotype. Therefore, the appropriate symbols are:L - long ears .l - short ears .Cross 1 is then: Ll X ll ----> 1:1 long ears : short earsCross 2 is then Ll X Ll ----> 3:1 long ears : short earsThe predictions agree with the data.Flowers:Cross 1: blue flowers X white flowers gives all pale blue flowers – a plausible model is thatcolor is controlled by one gene with 2 alleles, resulting in blue and white flowers, and thatneither phenotype is dominant. This is an example of co-complete dominance.BB - blue phenotype.B'B' - white phenotype.BB' - pale blue phenotype.therefore:Cross 1 is then: BB X B'B' ----> all BB', pale blue flowers .Cross 2 is then: BB' X BB' ----> 1:2:1 BB, blue flowers : BB', pale blue flowers : B'B',whiteflowers. The predictions agree with the data.Blood TypeBlood type is determined by one gene that has three alleles:IA - allele associated with the A phenotype, co-dominant with the B phenotypeIB - allele associated with the B phenotype, co-dominant with the A phenotypeIO - allele associated with the O phenotype, recessive to both the A and B phenotypea) Cross 1 is then: IAIA X IBIB ----> all type IAIBCross 2 is then: IAIB X IAIB ----> 1:2:1 types A:AB:B (note skewed ratio with small numberof progeny)b) Cross 1 is then: IAIO X IBIO----> 1:1:1:1 types A:B:AB:O (note skewed ratio with smallnumber of progeny)The predictions agree with the data.Mice II:a) Tail-lessness and lethality are controlled by one gene with two alleles:T allele - dominant tail-less phenotype; recessive lethal phenotypet allele - recessive normal-tail phenotype; dominant viable phenotypetherefore:TT - tail-less and deadTt - tail-less and alivett - normal-tail and aliveCross 1 is then: Tt X tt ----> 1:1, Tt (tail-less) : tt (normal)Cross 2 is then: Tt X Tt ----> 1:2:1 normal:tail-less:deadThe predictions agree with the data.b) eye color is determined by one gene with two alleles:B - dominant blue-eye phenotypeb - recessive brown eye phenotypetooth length is determined by one gene with two alleles:T - dominant short-tooth phenotypet - recessive long tooth phenotypeCross 1 is then: BBss X bbSS ----> all BbSsCross 2 is then: BbSs X BbSs ----> 9:3:3:1 (B_S_): (B_ss): (bbS_): (bbss)The predictions agree with the data.PlantsHeight is determined by one gene with two alleles where the tall phenotype is dominantover the short phenotype.Color is determined by one gene with two alleles where the green phenotype is dominantover the yellow phenotype.Cross 1 is then: TtGG X ttgg ----> 1:1 tall and green (TtGg) : short and yellow ( ttGg)Cross 2 is then: TTGg X ttgg ----> 1:1 (tall and green (TtGg) : tall and yellow
View Full Document
Unlocking...