3.25: Predict Probabilities of Outcomes from Monohybrid Crosses

MONOHYBRID CROSSES: Determines the Allele combinations of offspring for one particular gene only


METHOD:

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STEP 1: Designate characters to represent Alleles

• Capital letter represents a Dominant Allele, lower case letter represents Recessive Allele

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STEP 2: Write down the Genotype and Phenotype of the parents

• This is the Parental generation (P generation)

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STEP 3: Write down the genotype of Parental Gametes

• This will be haploid as a result of Meiotic division

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STEP 4: Use a Punnett grid to work out the potential gamete combinations

• As Fertilisation is random, all combinations have equal probability

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STEP 5: Write out the Genotype and Phenotype ratios of potential offspring

• This is F1 generation (first filial generation)

• Subsequent generations through interbreeding labelled F2, F3, etc

EXAMPLE: Eye Colour

• B is a Dominant Allele for Brown Eyes

• b is a Recessive Allele for Blue Eyes

EYE COLOUR OF OFFSPRING
PHENOTYPES OF PARENTS	Brown Eyes                         Brown Eyes             (Heterozygous)                    (Heterozygous)
GENOTYPES OF PARENTS	Bb                                          Bb
GAMETES
GENOTYPES OF OFFSPRING
PHENOTYPES OF OFFSPRING
RATIO	Brown Eyes   =    ¾               Blue Eyes      =    ¼