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9-2 Genetic Crosses
Genotype and Phenotype
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Genotype- genetic makeup
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Phenotype- physical appearance
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Homozygous- two same alleles
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Heterozygous- two different alleles, dominant expressed
Probability
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Probability- likelihood that a specific event will occur
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Expressed as fraction or ratio
Predicting Results of Monohybrid Crosses
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Monohybrid cross- only one characteristic is tracked
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Punnett square- diagram used to predict possible offspring
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Homozygous x Homozygous- 100% Pp, 100% purple
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Homozygous x Heterozygous- 50% PP, 50% Pp, 100% purple
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Genotypic ratio- ratio of genotypes (AA:Aa:aa)
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Phenotypic ratio- ratio of phenotypes (Purple:brown)
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Testcross- used to determine whether dominant is homozygous or heterozygous
o Crossed with recessive- if any recessive offspring produced, then
heterozygous parent
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Complete dominance- only two possible phenotypes
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Incomplete dominance- heterozygous appears between homozygous phenotypes
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Codominance- neither allele is dominant or recessive, both equally expressed
Predicting Results of Dihybrid Crosses
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Dihybrid cross- two characteristics are tracked
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Homozygous x Homozygous- all heterozygous
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Heterozygous x Heterozygous
o 9/16 both dominant phenotype, 3/16 each one dominant & one recessive,
1/16 both recessive