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BIOLOGY
Asked by Jess

How do you work out the percentage of someone with blue eyes from a genetic diagram? (BB, BB, BB in a table?

How to construct Punnett squares. Determine the parental genotypes. You can use any letter you like but select one that has a clearly different lower case, for example: Aa, Bb, Dd. Split the alleles for each parent and add them into your Punnett square around the edges. Work out the new possible genetic combinations inside the Punnett square. You may be asked to comment on the proportion of different allele combinations in the offspring, calculate a probability, ratio or just determine the phenotypes of the offspring.

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Heaja Sadiq
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How to construct Punnett squares. Determine the parental genotypes. You can use any letter you like but select one that has a clearly different lower case, for example: Aa, Bb, Dd. Split the alleles for each parent and add them into your Punnett square around the edges. Work out the new possible genetic combinations inside the Punnett square. You may be asked to comment on the proportion of different allele combinations in the offspring, calculate a probability, ratio or just determine the phenotypes of the offspring.

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Heaja Sadiq
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Using penette square

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Asha Sooriyakumar
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If it’s just one characteristic the table is referred to as a monohybrid cross, so there should be four possible outcomes. For example if the parents are both heterozygous (Bb) with B= brown eyes and b= blue eyes, the outcomes will be BB, Bb, Bb, bb. The capital letters represent dominant alleles, so only one needs to be present to code for the particular characteristic it corresponds to- so 3/4 or 75% of the offspring will have Brown eyes. The allele for blue eyes is recessive, so is represented by a lower case letter. For the characteristic of a recessive allele to be coded for, both alleles need to be recessive (so the genotype will be homozygous recessive). Therefore the only allele combination which will give blue eyes is bb, meaning the remaining 25% will have blue eyes. Hope this is helpful.

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Isabelle Walker
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