INTRO TO PUNNETT SQUARES3/6/19

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DO NOW ‣ What are the similarities between meiosis and

mitosis?

‣ What are the differences between meiosis and mitosis?

AGENDA▸ Introduction to Punnett Squares

▸Quiz next Monday (Mutations, Chromosomes, Meiosis/mitosis, and Punnett Squares)

INTRODUCTION TO PUNNETT SQUARES

CORNELL NOTES TITLE (PAGE 119, 121)

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INQUIRY▸ Copy the statement below and determine

whether you agree or disagree with it:

• Two parents with blue eyes can have a child with brown eyes

ALLELES▸ A different form of a gene

▸ Represented by letters: AA, Aa, aa

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EXPRESSED TRAIT▸ When a gene is manifested in a physical

form

▸ Not all genes in your body are expressed!

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DOMINANT ALLELE▸ Allele that will always express if present in

the genes

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RECESSIVE ALLELE▸ An allele that will express only when there is

no dominant allele

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HOMOZYGOUS DOMINANT▸ Homo = same, Zygous = zygote

▸ Both alleles are dominant

▸ AA

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HOMOZYGOUS RECESSIVE▸ Both alleles are recessive

▸ aa

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HETEROZYGOUS▸ Hetero = different

▸ Heterozygous = one allele is dominant, one allele is recessive

▸ Aa

▸ AKA carriers

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GENOTYPE▸ Genetic make up for a specific individual

▸ AA, Aa, aa

▸ Homozygous dominant, heterozygous, homozygous recessive

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PHENOTYPE▸ Physical manifestation of the genotype

▸ Blue eyes, brown eyes

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GENOTYPE VS. PHENOTYPE

WHICH ALLELES ARE EXPRESSED?▸ B = brown eyes, b = blue eyes

▸ BB =

▸ bb=

▸ Bb=

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WHICH ALLELES WILL BE EXPRESSED?▸ Dominant trait will always express if present

▸ Recessive alleles will only be expressed when there are NO dominant alleles

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IF YOU CAN’T SEE IT, DOES IT MEAN IT’S NOT THERE?▸ Heterozygous (carriers) “carry” the recessive

genes, even if they don’t show up in the phenotype

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WHICH ALLELE WILL BE EXPRESSED?

• W = widow’s peak, w = no widow’s peak

• WW =

• ww=

• Ww=

WHAT IS A POSSIBLE GENOTYPE OF THIS INDIVIDUAL?

• W = widow’s peak, w = no widow’s peak

WHAT IS A POSSIBLE GENOTYPE OF THIS INDIVIDUAL?

• B = brown eyes, b = blue eyes

WHAT IS A POSSIBLE GENOTYPE OF THIS INDIVIDUAL?

• P = purple flower, p = white flower

WHICH ALLELE IS DOMINANT?

WHICH ALLELE IS DOMINANT?

• Detached earlobes are dominant!

CONNECTION TO MEIOSIS▸One allele (in one chromosome) from mom

▸One allele (in one chromosome) from dad

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GENETIC CROSS▸When an egg is fertilized, the alleles of the

sperm will mix with the alleles of the egg

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PROBABILITY• CHANCE that something will occur

• 1/4 = 25%

• 2/4 = 1/2 = 50%

• 3/4 = 75%

• 4/4 = 1 = 100%

PUNNETT SQUARES▸ Tool used to predict the outcome of a

genetic cross

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HOW TO USE PUNNETT SQUARES▸ Cross Bb x bb Genotypes:

▸ Phenotypes:

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EXAMPLE 1▸ B = Brown eyes, b = blue eyes

▸ BB x bb

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EXAMPLE 2▸W = widow’s peak, w = no widow’s peak

▸ Homozygous recessive mom, heterozygous dad

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