Punnett square notes
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Punnett Square Notes. Crossing Traits. We use Punnett Squares to cross parents traits. This gives us a percentage to be able to determine an offspring’s possible traits. We represent traits with letters. Dominant traits are represented with a capital letter.

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Punnett Square Notes

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Punnett square notes

Punnett Square Notes


Crossing traits

Crossing Traits

  • We use Punnett Squares to cross parents traits. This gives us a percentage to be able to determine an offspring’s possible traits.

  • We represent traits with letters.

  • Dominant traits are represented with a capital letter.

  • Recessive traits are represented with a lower case letter.

  • Since each parent passes on half of an offsprings traits, each person has two letters, one from mom and one from dad. We refer to these letters as “alleles”.


Expressing traits

Expressing Traits

  • If an offspring possesses the dominant trait, it can be expressed one of two ways:

    DDorDd

  • Recessive traits can only be expressed as:

    dd


Naming

Naming

  • Each one of these ways has a specific name.

    • DD  homozygous dominant

    • Dd  heterozygous OR heterozygous dominant

    • dd  homozygous recessive

both alleles are the same a dominant gene was passed on

alleles are different a dominant gene was passed on

both alleles are the same only recessive genes were passed on


Other vocab

Other Vocab

  • purebreed: homozygous dominant or homozygous recessive

  • hybrid: heterozygous

  • genotype: trait represented by letters

    • Genetic makeup

  • phenotype: the physical representation of the genotype

    • How we see the traits


Putting it all together

Putting it all together

Example 1:

Trait: Dimples

(having dimples is dominant, NOT having dimples is recessive)

Mom: homozygous dominant

-genotype: DD

-phenotype: dimples

Dad: homozygous recessive

-genotype: dd

-phenotype: NO dimples


Creating the punnett square

Creating the Punnett Square

DD

Parent 1 Genotypes

d

d

Capital letters

are ALWAYS

written first!!

Parent 2 Genotypes

Possible genotypes for offspring: Dd

Possible phenotypes: dimples


Putting it all together1

Putting it all together

Example 2:

Trait: Freckles

(having freckles is dominant, NOT having freckles is recessive)

Mom: homozygous recessive

-genotype: ff

-phenotype: NO freckles

Dad: heterozygous

-genotype: Ff

-phenotype: freckles


Creating the punnett square1

Creating the Punnett Square

ff

Possible genotypes for offspring:

Ffff

Possible phenotypes:

freckles no freckles

What are the chances of a child having freckles?

2 out of 4 OR 50%

What are the chances of a child NOT having freckles?

2 out of 4 OR 50%

F

f


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