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Punnet Squares and Punnet Squares and Blood TypesBlood Types
Mrs. McCarthyMrs. McCarthy
April 21, 2023April 21, 2023
I. Punnett Square- I. Punnett Square- helpful way of showing results from helpful way of showing results from any crossany crossEx. If a purebred tall pea plant is crossed with a purebred short pea plant, the Ex. If a purebred tall pea plant is crossed with a purebred short pea plant, the Punnett Square will show Punnett Square will show the probabilitythe probability of the offspring from this cross of the offspring from this cross
A. Probability- A. Probability- chance of how often something will chance of how often something will occur, often written in a percentoccur, often written in a percent
B. Ratio- B. Ratio- numerical expression showing the numerical expression showing the relationship between two occurrencesrelationship between two occurrences
Ex. Ex. 1:21:2 or or 50% 50% or or 1/21/2 3:43:4 or or 75% 75% oror 3/4 3/4
Note: Like fractions, ratios should Note: Like fractions, ratios should ALWAYSALWAYS be be written in its lowest form. written in its lowest form.
Ex. 2:6 should be written as Ex. 2:6 should be written as 1:3 or 33%1:3 or 33%
II. Review:II. Review:
A. Monohybrid cross- A. Monohybrid cross- a cross that involves a cross that involves one pair of contrasting traitsone pair of contrasting traits
B. Dihybrid cross- B. Dihybrid cross- a cross that involves a cross that involves two pairs of contrasting traitstwo pairs of contrasting traits
III. How a Punnett Square WorksIII. How a Punnett Square Works
A. Punnett squares are written using the A. Punnett squares are written using the alleles in the genotypealleles in the genotype
TTTT TtTt
TT TT TT tt
1. Remember the law of segregation! The alleles separate during meiosis. Each gamete gets only ONE allele!
IV. Monohybrid Punnett Square IV. Monohybrid Punnett Square PracticePractice
Monohybrid crosses:Monohybrid crosses:
1. In peas, yellow seeds are dominant to green 1. In peas, yellow seeds are dominant to green seeds. Cross a heterozygous yellow plant with a seeds. Cross a heterozygous yellow plant with a homozygous recessive (green) plant.homozygous recessive (green) plant.
Step 1: Step 1: Write out genotype and phenotypes: Write out genotype and phenotypes: Y=yellow Y=yellow y=greeny=green
Step 2: Step 2: Write out cross: Yy Write out cross: Yy ●● yy yy
Monohybrid Punnet Square Monohybrid Punnet Square PracticePractice
Step 3: Step 3: Complete a Complete a punnett punnett squaresquare
YY yy
yy
yy
YyYy
YyYy
yyyy
yyyy
Step 4: Step 4: List your final results by genotypes and List your final results by genotypes and phenotypes with the proper ratiophenotypes with the proper ratio
GenotypeGenotype PhenotypePhenotype
½ Yy½ Yy ½ Yellow½ Yellow
½ yy½ yy ½ Green½ Green
Monohybrid Punnet Square Monohybrid Punnet Square PracticePractice
2. Cross a heterozygous round seed plant with 2. Cross a heterozygous round seed plant with another heterozygous round seed plant. another heterozygous round seed plant.
R= roundR= round r= wrinkledr= wrinkled
Rr ● RrRr ● Rr
RR rr
RR
rr
RRRR
RrRr
RrRr
rrrr
GenotypeGenotype PhenotypePhenotype
¼ RR¼ RR ¼ Round¼ Round
½ Rr½ Rr ½ Round½ Round
¼ rr¼ rr ¼ wrinkled¼ wrinkled
Monohybrid Punnet Square Monohybrid Punnet Square PracticePractice
3. In guinea pigs, black fur is dominant to white fur. 3. In guinea pigs, black fur is dominant to white fur. Cross a homozygous dominant parent with a Cross a homozygous dominant parent with a homozygous recessive parent.homozygous recessive parent.
B= BlackB= Black b= whiteb= white
BB ● bbBB ● bb
BB BB
bb
bb
BbBb
BbBb
BbBb
BbBb
GenotypeGenotype PhenotypePhenotype
4/4 Bb4/4 Bb All BlackAll Black
V. Dihybrid Punnett Square V. Dihybrid Punnett Square PracticePractice
Dihybrid Cross: Dihybrid Cross: 1. Cross a homozygous round, green pea with a wrinkled, 1. Cross a homozygous round, green pea with a wrinkled,
heterozygous yellow pea.heterozygous yellow pea.Step 1: Step 1: Write out genotype and phenotypeWrite out genotype and phenotype
R= roundR= round Y= yellowY= yellowr= wrinkledr= wrinkled y=green y=green
Step 2: Step 2: Show your crossShow your crossRRyy ● rrYyRRyy ● rrYy
Step 3: Step 3: Show the different types of combinations in Show the different types of combinations in gametes.gametes.
RRyyRRyy RyRy rrYyrrYy rY, ryrY, ry
Dihybrid Punnet Square PracticeDihybrid Punnet Square Practice
Step 4: Step 4: Show your punnet squareShow your punnet square
rYrY ryry
RyRy RrYyRrYy RryyRryy
Step 5: Step 5: Show your genotypes and phenotypesShow your genotypes and phenotypesGenotypeGenotype PhenotypePhenotype
½ RrYy½ RrYy ½ Round, Yellow½ Round, Yellow
½ Rryy½ Rryy ½ Round, green½ Round, green
Dihybrid punnet square practiceDihybrid punnet square practice
2. Cross a heterozygous round, yellow plant with a heterozygous 2. Cross a heterozygous round, yellow plant with a heterozygous round, green plant.round, green plant.
R= Round Y=YellowR= Round Y=Yellowr= wrinkled y= greenr= wrinkled y= green
RrYy ● RryyRrYy ● RryyGametes=RY, Ry, ry, rY and Ry, ryGametes=RY, Ry, ry, rY and Ry, ry
RYRY RyRy
RyRy
ryry
RRYyRRYy
RrYyRrYy
RRyyRRyy
RryyRryy
ryry rYrY
RryyRryy
rryyrryy rrYyrrYy
RrYyRrYy
GenotypeGenotype PhenotypePhenotype
1/8 RRYy1/8 RRYy 1/8 Round, 1/8 Round, YellowYellow
1/8 RRyy1/8 RRyy 1/8 Round, 1/8 Round, YellowYellow
¼ Rryy¼ Rryy ¼ Round, ¼ Round, greengreen
1/8 rryy1/8 rryy 1/8 wrinkled, 1/8 wrinkled, greengreen
1/8 rrYy1/8 rrYy 1/8 wrinkled, 1/8 wrinkled, yellowyellow
¼ RrYy¼ RrYy ¼ Round, ¼ Round, YellowYellow
VI. Blood TypesVI. Blood Types
A. Co-dominance- A. Co-dominance- two dominant alleles are expressed at the two dominant alleles are expressed at the same timesame time
Ex. Ex. Type AB bloodType AB blood
B. Multiple Alleles- B. Multiple Alleles- genes with three or more allelesgenes with three or more allelesEx. Ex. Blood TypesBlood Types
C. Blood Type Alleles:C. Blood Type Alleles:A= A= IIAAIIAA or I or IAAii B= B= IIBBIIBB or I or IBBiiO= O= iiii AB= AB= IIAAIIBB
Cross the same as a regular monohybrid crossCross the same as a regular monohybrid cross!!
Blood TypesBlood Types
1.1. Cross a homozygous type A man with a type Cross a homozygous type A man with a type O woman.O woman.
IIAAIIA A ● ii● ii
IIAA IIAA
ii
ii
IIAAii
IIAAii
IIAAii
IIAAii
GenotypeGenotype PhenotypePhenotype
4/4 I4/4 IAAii All type AAll type A
Blood TypesBlood Types
2. Cross a heterozygous type A man with a 2. Cross a heterozygous type A man with a heterozygous type B woman.heterozygous type B woman.
IIAAi ● Ii ● IBBii
IIAA ii
IIBB
ii
IIAAIIBB
IIAAii
IIBBii
iiii
GenotypeGenotype PhenotypePhenotype
¼ I¼ IAAIIBB ¼ Type AB¼ Type AB
¼ I¼ IAAii ¼ type A¼ type A
¼ I¼ IBBii ¼ type B¼ type B
¼ ii¼ ii
¼ type O¼ type O
HomeworkHomework
Complete Genetics Worksheet #1Complete Genetics Worksheet #1
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